manual 789c - 785c

Service TrainingMeeting Guide 706 SESV1706

November 1998

TECHNICAL PRESENTATION

785C/789C OFF-HIGHWAY TRUCKS

785C/789C OFF-HIGHWAY TRUCKSMEETING GUIDE 706 SLIDES AND SCRIPT

AUDIENCE

Level II--Service personnel who understand the principles of machine systems operation, diagnosticequipment, and procedures for testing and adjusting.

CONTENT

This presentation provides basic maintenance information and describes the systems operation of theengine, power train, steering, hoist and the air system and brakes for the 785C/789C Off-highwayTrucks. The Automatic Retarder Control (ARC) and the Traction Control System (TCS) are alsodiscussed.

OBJECTIVES

After learning the information in this meeting guide, the serviceman will be able to:1. locate and identify the major components in the engine, power train, steering, hoist and the air

system and brakes;

2. explain the operation of the major components in the systems; and

3. trace the flow of oil or air through the systems.

REFERENCES

784C Tractor/785C Truck Service Manual SENR1485784C Tractor/785C Truck Operation and Maintenance Manual SEBU7173785C Truck with High Altitude Arrangement (HAA) Operation and Maintenance Manual SEBU7176789C Truck Service Manual SENR1515789C Truck Operation and Maintenance Manual SEBU7174Cold Weather Recommendations for Caterpillar Machines SEBU5898Caterpillar Machine Fluids Recommendations SEBU6250

PREREQUISITES

Interactive Video Course "Fundamentals of Mobile Hydraulics" TEMV9001Interactive Video Course "Fundamentals of Electrical Systems" TEMV9002STMG 546 "Graphic Fluid Power Symbols" SESV1546

Estimated Time: 24 HoursVisuals: 206 (2 X 2) SlidesServiceman Handouts: 16 Data SheetsForm: SESV1706

© 1998 Caterpillar Inc. Date: 11/98

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SUPPLEMENTAL MATERIAL

Reference Manuals

Vital Information Management System (VIMS) Service Manual SENR6059Fluid Power Graphic Symbols User's Guide SENR3981Flexxaire Fan Installation and Maintenance Manual SEBC1152

Specification Sheets

785C Off-highway Truck AEHQ5320789C Off-highway Truck AEHQ5321793C Update Off-highway Truck AEHQ5186

Salesgrams and Product Bulletins

Salesgram "Vital Information Management System (VIMS)" TELQ4478Training Bulletin "Caterpillar Transmission/Drive Train Oil" TEJB1002Product Bulletin "Reporting Particle Count By ISO Code" PEJT5025Salesgram "Caterpillar Extended Life Coolant" TEKQ0072Product Data Sheet "Caterpillar Extended Life Coolant" PEHP4036Salesgram "785C/789C/793C Mining Truck Introduction" TELQ4459Salesgram "Cat 769, 771, 773, 775, 777, 785 and 789 Flexxaire FanCustom Attachment" TELQ4010Product Bulletin "793C Off-highway Truck" TEJB3060

Technical Instruction Modules

Vital Information Management System--785B/789B/793B Off-highway Trucks SEGV2610Vital Information Management System--Introduction SEGV2597Electronic Programmable Transmission Control II SEGV2584769C - 793B Off-highway Trucks--Torque Converter andTransmission Hydraulic Systems SEGV2591785B/789B/793B Off-highway Trucks--Steering System SEGV2587769C - 793B Off-highway Trucks--Hoist System SEGV2594769C - 793B Off-highway Trucks--Air System and Brakes SEGV2595Automatic Retarder Control System SEGV2593Automatic Electronic Traction Aid SEGV2585769C - 793B Off-highway Trucks--Suspension System SEGV2599

Service Training Meeting Guides

STMG 682 "793C Off-highway Truck" SESV1682STMG 681 "3500B Engine Controls--Electronic Unit Injection (EUI)" SESV1681STMG 660 "785B/789B/793B Off-highway Trucks--Maintenance" SESV1660

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SUPPLEMENTAL MATERIAL (continued)

Video Tapes

793C Off-highway Truck--Service Introduction SEVN4016793C Off-highway Truck--Marketing Introduction AEVN3742Suspension Cylinder Charging TEVN2155Introduction to the Automatic Electronic Traction Aid (AETA) SEVN91873500 Engines--EUI Service Introduction SEVN2241Mining Trucks--Cleanliness and Component Life SEVN4142

Booklets

Know Your Cooling System SEBD0518Diesel Fuels and Your Engine SEBD0717Oil and Your Engine SEBD0640C-Series Mining Trucks--3500B Diesel Engines LEDH8400Understanding the S•O•S Report TEJB1015

Special Instructions

Personality Module Booklet--Injectors and Electronic Components SEHS9914Caterpillar Electronic Controls Service Code Information Description List REHS0126Use of CE Connector Tools SEHS9065Servicing DT Connectors SEHS9615Use of 6V3000 Sure-Seal Repair Kit SMHS7531Use of 8T5200 Signal Generator/Counter Group SEHS8579Suspension Cylinder Servicing SEHS9411Repair of Steering Accumulators SEHS8757Using the 147-5482 Valve Lash Adjustment Group REHS0128Using 1U5000 Auxiliary Power Unit SEHS8715Using 1U5525 Auxiliary Power Unit Attachments SEHS8880Mining Truck Major Component Removal and Installation Enhancement REHS0082785C Assembly Procedure REHS0263789C Assembly Procedure REHS0264

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SUPPLEMENTAL MATERIAL (continued)

Brochures

Caterpillar Electronic Technician NELS1007Caterpillar DataView NEHP5622Diesel Engine Oil (CH4) Product Data Sheet PEHP8038How to Take a Good Oil Sample PEHP6001S•O•S Coolant Analysis PEHP5033Air Filter Service Indicator PEHP9013Caterpillar Fully Automatic Transmission AEDQ0066Caterpillar Oil-cooled Multiple Disc Brakes AEDK2546Caterpillar Automatic Retarder Control AEDK0075Caterpillar Truck Frames AEDK0707Mining Truck Bodies: Selecting the Right Body System for Your Job AEDK0083C-Series Mining Truck Cabs YEBA3500

Miscellaneous

Window Decal "VIMS Keypad Parameters" SEEU6995Pocket Card "Electronic Diagnostic Codes" NEEG2500Chart "Practical Pressure Conversions" SEES5677Guideline for Reusable Parts "Cleaning Rear AxleHousing Assemblies (785/789)" SEBF8366

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TABLE OF CONTENTS

INTRODUCTION ........................................................................................................................7

WALK AROUND INSPECTION...............................................................................................11

OPERATOR'S STATION............................................................................................................45

ENGINE......................................................................................................................................65Engine Electronic Control System .......................................................................................66Cooling System.....................................................................................................................88Lubrication System ...............................................................................................................97Fuel System.........................................................................................................................101Air Induction and Exhaust System .....................................................................................106

POWER TRAIN .......................................................................................................................111Torque Converter ................................................................................................................112Torque Converter Hydraulic System...................................................................................115Transmission and Transfer Gears........................................................................................125Transmission Hydraulic System .........................................................................................128Differential ..........................................................................................................................138Final Drives.........................................................................................................................144Transmission/Chassis Electronic Control System ..............................................................145

STEERING SYSTEM ..............................................................................................................155

HOIST SYSTEM......................................................................................................................188

AIR SYSTEM AND BRAKES ................................................................................................208Air Charging System...........................................................................................................210Brake Systems.....................................................................................................................217

BRAKE ELECTRONIC CONTROL SYSTEM.......................................................................237Automatic Retarder Control (ARC)....................................................................................240Traction Control System (TCS) ..........................................................................................245

OPTIONAL EQUIPMENT.......................................................................................................253FlexxaireTM Fan ...................................................................................................................253

CONCLUSION.........................................................................................................................256

SLIDE LIST..............................................................................................................................257

SERVICEMAN'S HANDOUTS...............................................................................................260

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INTRODUCTION

Shown is the 789C Off-highway Truck. The "C" Series trucks are thesame as the "B" Series except for the following changes: 3500B engines,improved cab, two different Electronic Control Modules(Transmission/Chassis and Brake) and an electronically controlled hoist.The 789C also has a 40% larger cooling system with a shunt tank locatedabove the radiator.

The second generation Electronic Programmable Transmission Control(EPTC II) has been replaced with the Transmission/Chassis ElectronicControl System. The Transmission/Chassis Electronic Control Module(ECM) controls the same functions as the EPTC II plus the hoist andsome other functions.

The Automatic Retarder Control (ARC) and the Traction Control System(TCS) control modules have been replaced with one Brake System ECM.The Brake System ECM controls both the ARC and the TCS functions.The TCS is now connected to the CAT Data Link and the ElectronicTechnician (ET) service tool can be used to diagnose the TCS.

The load carrying capacities and the Gross Machine Weights (GMW) ofthe "C" Series trucks are:

785C: 118 to 136 Metric tons (130 to 150 tons) 249480 kg (550000 lb.) GMW

789C: 154 to 177 Metric tons (170 to 195 tons) 317520 kg (700000 lb.) GMW

• Load carryingcapacity

• 789C Off-highwayTruck

• Transmission/ChassisElectronic ControlSystem

• Brake ElectronicControl System

785C/789C OFF-HIGHWAY TRUCKS

© 1998 Caterpillar Inc.

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Shown is the right side of a 789C truck. The large air tank on the rightplatform supplies air for starting the truck and for the service and retarderbrake system.

The hoist, brake and torque converter hydraulic tank (rear) and thetransmission hydraulic tank (front) are also visible. The transmissionhydraulic system is separate from all the other hydraulic systems.

• Main system air tank:- Air starting

- Service/retarderbrakes

• Rear hydraulic tank:- Hoist system

- Brake system

- Torque converter

• Front hydraulic tank:- Transmission

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• 789C and 793C aresimilar

• 789C has two airfilters and verticalladders

• 793C has four airfilters and a diagonalladder

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Shown is the front of a 789C truck. The 789C is similar in appearance tothe 793C and may be difficult to identify from a distance. The 793C canbe identified by the four air filters and the diagonal access ladder. The789C has only two air filters and is equipped with two vertical ladders.

The "C" Series trucks use a folded core radiator. The folded core radiatorprovides the convenience of repairing or replacing smaller individualcores.

• Folded core radiator

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• Truck body options:- 12 degree flat floor

- Dual slope

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The truck bodies on "C" Series trucks are mandatory options. Two bodystyles are available for the "C" Series trucks:

- A 12 degree flat floor design that provides uniform load dumping,excellent load retention and a low center of gravity.

- A dual-slope design with a "V" bottom main floor to reduce shockloading, center the load and reduce spills.

All internal wear surfaces of the truck bodies are made with 400 Brinellhardness steel. All attachment body liners are also made with 400 Brinellhardness steel. The external components of the bodies are made of steelwith a yield strength of 6205 bar (90000 psi).

The forward two-thirds of the body floor is made with 20 mm (.79 in.)thick 400 Brinell steel plate. The rear one-third of the body floor is madewith a 10 mm (.39 in.) thick 400 Brinell sub plate and a 20 mm (.79 in.)thick 400 Brinell body grid liner plate. As an option, the grid liner platecan be made with 500 Brinell steel.

The rear suspension cylinders absorb bending and twisting stresses ratherthan transmitting them to the main frame.

• Rear suspensioncylinders

• Internal wear surface

• External bodycomponents

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• Read the Operationand MaintenanceManual

785C/789C MAINTENANCE

789C Service

Procedure

WALK AROUND INSPECTION

WALK AROUND INSPECTION

Before working on or operating the truck, read the Operation andMaintenance Manual thoroughly for information on safety, maintenanceand operating techniques.

Safety Precautions and Warnings are provided in the manual and on thetruck. Be sure to identify and understand all symbols before starting thetruck.

The first step to perform when approaching the truck is to make athorough walk around inspection. Look around and under the truck forloose or missing bolts, trash build-up and for coolant, fuel or oil leaks.Look for indications of cracks. Pay close attention to high stress areas asshown in the Operation and Maintenance Manual.

INSTRUCTOR NOTE: The form numbers for the Operation andMaintenance Manuals are provided under "References" on Page 2.

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STEERING OIL LEVEL

BATTERIES

COOLANT LEVEL

WHEEL NUTS

ENGINE OIL LEVEL

AIR FILTER,RESTRICTION INDICATORS

AND PRECLEANERS

FUEL LEVEL ANDDRAIN MOISTURE

TRANSMISSIONOIL LEVEL HOIST, CONVERTER

AND BRAKE OIL LEVEL

BELTS AND ETHER CYLINDERS

TIRE INFLATIONPRESSURE

SUSPENSION CYLINDER HE

SUSPENSION CYLINDER HEIGHT,GREASE BREATHERS

AND WHEEL BREATHERS

REAR AXLE ANDBRAKE CYLINDER

BREATHERS

FRAME FOR CRACKS ANDBODY SUPPORT PADS

LEAKS AND TRASH BUILD-UPAIR RESERVOIR MOISTURE

WINDSHIELD WASHER LEVELAND A/C FILTER

AUTO LUBE RESERVOIR

REAR AXLE OIL LEVEL

WASH WINDOWS,CAB FRESH AIR FILTERS,

SEAT BELT, INDICATORS, GAUGES,BRAKE TESTS

SECONDARY STEERING ANDBACK-UP ALARM

10 HOURS/DAILY MAINTENANCE CHECKS

The following list identifies the items that must be serviced every 10Hours or Daily.

- Walk around inspection: Check for loose or missing bolts, leaks andcracks in frame structures

- Suspension cylinders: Measure/recharge- Transmission oil: Check level- Hoist, converter and brake system oil: Check level- Rear axle oil: Check level- Fuel tank: Drain moisture- Engine crankcase oil: Check level- Radiator: Check level and radiator core plugging- Air filters and precleaners: Check restriction indicators and

precleaner dirt level- Steering system oil: Check level- Air tanks: Drain moisture- Brakes: Check operation- Indicators and gauges: Test operation- Seat belt: Inspect- Back-up alarm: Test operation- Secondary steering: Test operation

• Maintenance

- 10 hours/daily

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• Front wheel bearinginspection plug(arrow)

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The front wheel bearing oil level is checked and filled by removing theplug (arrow) in the center of the wheel bearing cover. The oil should belevel with the bottom of the plug hole.

The service interval for changing the front wheel bearing oil has beenreduced from 2000 hours to 500 hours.

Use only Transmission Drive Train Oil (TDTO) with a specification ofTO-4 or newer. TDTO TO-4 provides increased lubrication capability forbearings.

Check the tire inflation pressure. Operating the truck with the wrong tireinflation pressure can cause heat build-up in the tire and accelerate tirewear.

NOTE: Care must be taken to ensure that fluids are contained whileperforming any inspection, maintenance, testing, adjusting andrepair of the machine. Be prepared to collect the fluid in suitablecontainers before opening any compartment or disassembling anycomponent containing fluids. Refer to the "Tools and Shop ProductsGuide" (Form NENG2500) for tools and supplies suitable to collectand contain fluids in Caterpillar machines. Dispose of fluidsaccording to local regulations and mandates.

• Tire inflation

• Use only TDTO oil

• Oil change interval500 hours

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1

2

Check the front suspension cylinders for leaks or structural damage.Check the charge condition of the front suspension cylinders when thetruck is empty and on level ground. Measure the charge height of thesuspension cylinders and compare the dimension with the dimension thatwas recorded the last time the cylinders were charged. Recharge thecylinders with oil and nitrogen if necessary.

Inspect the condition of the front wheel bearing axle housing breather (1).The breather prevents pressure from building up in the axle housing.Pressure in the axle housing may cause brake cooling oil to leak throughthe Duo-Cone seals in the wheel brake assemblies.

Two grease outlet fittings (2) are located on the front of each suspensioncylinder. The grease supply line for the Auto Lubrication System islocated at the rear of the suspension cylinder. No grease outlet fittingsshould be located on the same side of the suspension cylinder as thegrease fill location. An outlet fitting positioned on the same side of thesuspension cylinder as the grease fill location will prevent properlubrication of the cylinder.

Make sure that grease is flowing from the outlet fittings to verify that thesuspension cylinders are being lubricated and that the pressure in thecylinders is not excessive.

INSTRUCTOR NOTE: For more detailed information on servicingthe suspension system, refer to the Special Instruction "SuspensionCylinder Servicing" (Form SEHS9411) and the Technical InstructionModule "769C - 793B Off-highway Trucks--Suspension System" (Form SEGV2599)

2. Suspension cylindergrease outlet fittings

• Make sure greaseflows from fittings

1. Front wheel bearingaxle housingbreather

• Front suspensioncylinder charge

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1. Dust valve

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2

1

On the 785C truck, an air filter housing and a precleaner are locatedbehind the front wheels on both sides of the truck. Check the dust valves(1) for plugging. If necessary, disconnect the clamp and open the coverfor additional cleaning.

The dust valve is OPEN when the engine is OFF and closes when theengine is running. The dust valve must be flexible and close when theengine is running or the precleaner will not function properly and theservice life of the air filters will be reduced. Replace the rubber dustvalve if it becomes hard and brittle.

The "C" Series trucks may have the optional primary fuel filters with awater separator (2). Two primary filter/water separators are installed, oneon each side of the truck. Open the drain valve at the bottom of eachhousing to drain the water when required. The drain interval isdetermined by the humidity of the local climate.

Replace the filter element in each housing every 500 hours or whenrestricted. The filter elements are removed from the top of the housings.

• Replace dust valve ifnot flexible

2. Primary fuelfilter/water separator

- Drain water

- Replace filter

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• 3512B engine

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Shown is the right side of the 3512B engine used in the 784C tractor and785C truck.

Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S)tap (arrow) located in the tube between the engine oil cooler and theengine oil filters.

• Engine oil S•O•S tap(arrow)

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1. Transmissioncharging filter

2. Transmission lubefilter

3. Torque convertercharging filter

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3

12

54

Located behind the right front tire is the transmission charging filter (1),the transmission lube filter (2), and the torque converter charging filter (3). Transmission oil samples can be taken at the Scheduled OilSampling (S•O•S) tap (4).

An oil filter bypass switch is located on each filter. The transmission oilfilter bypass switches provide input signals to the Transmission/ChassisECM. The Transmission/Chassis ECM sends the signals to the VIMS,which informs the operator if the filters are restricted. The torqueconverter charging filter bypass switch provides an input signal directly tothe VIMS.

One of the three injector banks (5) for the automatic lubrication system isalso in this location. These injectors are adjustable and regulate thequantity of grease that is injected during each cycle.

A solenoid air valve provides a controlled air supply for the automaticlubrication system. The solenoid air valve is controlled by the VitalInformation Management System (VIMS), which energizes the solenoidten minutes after the machine is started. The VIMS energizes thesolenoid for 75 seconds before it is de-energized. Every 60 minutesthereafter, the VIMS energizes the solenoid for 75 seconds until themachine is stopped (shut down). These settings are adjustable through theVIMS keypad in the cab.

INSTRUCTOR NOTE: For more detailed information on servicingthe automatic lubrication system, refer to the Service Manual module"Automatic Lubrication System" (Form SENR4724).

4. Transmission S•O•Stap

5. Automatic lubricationinjector bank

• Auto lubricationadjustment

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1. Transmissionhydraulic tank

2. Hoist, converter andbrake hydraulic tank

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1

4

2

3

Shown are the transmission hydraulic tank (1) and the hoist, converter andbrake hydraulic tank (2). Both tanks are equipped with oil level sightgauges.

The oil level of both hydraulic tanks should first be checked with cold oiland the engine stopped. The level should again be checked with warm oiland the engine running.

The lower sight gauge (3) on the hoist, converter and brake hydraulic tankcan be used to fill the tank when the hoist cylinders are in the RAISEDposition. When the hoist cylinders are lowered, the hydraulic oil levelwill increase. After the hoist cylinders are lowered, check the hydraulictank oil level with the upper sight gauge.

Inspect the hoist, converter and brake hydraulic tank breather (4) and thetransmission hydraulic tank breather (behind the mud flap) for plugging.

4. Hoist, converter andbrake tank breather

• Transmission tankbreather (behind mudflap)

3. Lower sight gaugefor oil level withraised cylinders

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When filling the hydraulic tanks after an oil change, fill the tanks with oilto the FULL COLD mark on the sight gauge. Turn on the engine manualshutdown switch (see Slide No. 25) so the engine will not start. Crank theengine for approximately 15 seconds. The oil level will decrease as oilfills the hydraulic systems. Add more oil to the tanks to raise the oil levelto the FULL COLD mark. Crank the engine for an additional 15 seconds.Repeat this step as required until the oil level stabilizes at the FULLCOLD mark.

Turn off the engine manual shutdown switch and start the engine. Warmthe hydraulic oil. Add more oil to the tank as required to raise the oillevel to the FULL WARM mark.

In both tanks, use only Transmission Drive Train Oil (TDTO) with aspecification of TO-4 or newer.

TDTO TO-4 oil:

- Provides maximum frictional capability required for clutch discsused in the transmission, torque converter and brakes.

- Increases rimpull because of reduced slippage.

- Increases brake holding capability by reducing brake slippage.

- Controls brake chatter.

- Provides maximum frictional capability required for gears.

NOTICEFailure to correctly fill the hydraulic tanks after an oil change maycause component damage.


• Tank refill procedure

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• Final drives

• Check magnetic plugs(arrow) for metal

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The rear axles are equipped with double reduction planetary final drives.The magnetic plug (arrow) should be removed from the final drives atregular intervals and checked for metal particles. For some conditions,checking the magnetic plug is the only way to identify a problem whichmay exist.

Use only Transmission Drive Train Oil (TDTO) with a specification ofTO-4 or newer.

TDTO TO-4 oil provides:

- Maximum frictional capability required for gears.

- Increased lubrication capability for bearings.

NOTICE

The rear axle housing is a common sump for the differential and bothfinal drives. If a final drive or the differential fails, the other finaldrive components must also be checked for contamination and thenflushed. Failure to completely flush the rear axle housing after afailure can cause a repeat failure within a short time.


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1. Differential oil levelsight glass

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22

4

1

3

5

The differential oil level is checked by viewing the oil level sight glass (1). The oil should be level with the bottom of the inspection hole.

Two oil level sensors (2) provide input signals to the Brake ECM. TheBrake ECM sends the signals to the VIMS, which informs the operator ofthe rear axle oil level. A rear axle oil filter (3) removes contaminantsfrom the rear axle housing.

Check the rear suspension cylinders for leaks or structural damage.Check the charge condition of the rear suspension cylinders when thetruck is empty and on level ground. Measure the charge height of thesuspension cylinders and compare the dimension with the dimension thatwas recorded the last time the cylinders were charged. Recharge thecylinders with oil and nitrogen if necessary.

The second of three injector banks (4) for the automatic lubricationsystem is mounted on the top rear of the differential housing.

Above the lubrication injectors is a breather (5) for the rear axle. Inspectthe condition of the breather at regular intervals. The breather preventspressure from building up in the axle housing. Excessive pressure in theaxle housing can cause brake cooling oil to leak through the Duo-Coneseals in the wheel brake assemblies.

INSTRUCTOR NOTE: For more detailed information on servicingthe suspension system, refer to the Special Instruction "SuspensionCylinder Servicing" (Form SEHS9411).

2. Rear axle oil levelsensors

3. Rear axle housingoil filter

• Rear suspensioncylinders

4. Automaticlubrication injectorbank

5. Rear axle breather

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• Cable holds body up

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The cable that holds the body up is stored below the rear of the body.Whenever work is to be performed while the body is raised, the safetycable must be connected between the body and the rear hitch to hold thebody in the raised position.

The space between the body and the frame becomes a zero clearancearea when the body is lowered. Failure to install the cable can resultin injury or death to personnel working in this area.

The cable will not hold if the hoist control lever is used to powerdown the body. Always disconnect the hoist valve cylinder linkagewhen working below the body.

WARNING

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• Fuel tank

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The fuel tank is located on the left side of the truck. The fuel level sightgauge (arrow) is used to check the fuel level during the walk aroundinspection.

The percentage of sulfur in the fuel will affect the engine oilrecommendations. The following is a summary of fuel sulfur and oilrecommendations:

1. Use API CH-4 performance oils.2. With fuel sulfur below 0.5%, any API CH-4 oils will have a

sufficient Total Base Number (TBN) for acid neutralization.3. For fuel sulfur values above 0.5%, the new oil TBN should be a

minimum of 10 times the fuel sulfur.4. When 10 times the fuel sulfur exceeds the oil TBN, reduce the oil

change interval to approximately one-half the normal changeinterval.

• Fuel level sight gauge(arrow)

• Fuel information

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1. Primary fuel filter

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2

3

1

The primary fuel filter (1) is mounted on the inner side of the fuel tank.

Open the drain valve (2) to remove condensation from the fuel tank.

A fuel level sensor (3) is also located on the fuel tank. The fuel levelsensor provides input signals to the VIMS which informs the operator ofthe fuel level.

3. Fuel level sensor

2. Condensation drainvalve

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31

Located in front of the fuel tank is the parking brake release filter (1) andthe torque converter outlet screen (2).

An oil filter bypass switch is located on each housing. The parking brakefilter bypass switch provides an input signal to the Brake ECM and thetorque converter outlet screen bypass switch provides an input signal tothe VIMS. The Brake ECM sends the signal to the VIMS, which informsthe operator if the filter or screen are restricted.

The 789C trucks have two air dryers (3) to accommodate the larger four-cylinder air compressor. Shown is the rear of the two air dryers.

The third injector bank for the automatic lubrication system is alsolocated in this area.

1. Parking brake releasefilter

2. Torque converter

3. 789C rear air dryer

• Automatic lubricationinjector bank

• Filter bypass switches

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1. Brake cylinderbreathers

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11

Inspect the condition of the three breathers (1) (two visible) for the brakecylinders. The third breather is located on the front brake master cylinderbehind the cross tube. Oil should not leak from the breathers. Oil leakingfrom the breathers is an indication that the oil piston seals in the brakecylinder need replacement. Air flow from the breathers during a brakeapplication indicates that the brake cylinder air piston seals needreplacement.

If air is in the system or a loss of oil downstream from the cylindersoccurs, the piston in the cylinder will overstroke and cause an indicatorrod to extend and open the brake overstroke switch (2). The switchprovides an input signal to the VIMS, which informs the operator of thecondition of the service and retarder brake oil circuit. If an overstrokecondition occurs, the problem must be repaired and the indicator rodpushed in to end the warning.

2. Brake overstrokeswitch

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31

On the 789C truck, the second air dryer (1) is located in front of the leftfront suspension cylinder. On the 785C truck, the only air dryer is locatedhere.

The air system can be charged from a remote air supply through a groundlevel connector (2) inside the left frame.

Engine oil can be added at the quick fill connector (3).

Use only Diesel Engine Oil (DEO) with a specification of CF-4 or newer.DEO oil with a CH-4 specification is available and should be used ifpossible.

CH-4 engine oil:

- Requires more performance tests than previous oils, such as CE orCF, and has a narrower performance band.

- Can withstand higher temperatures before coking and has betterdispersing capability for controlling soot.

- Has better fuel sulfur neutralization capability.

1. 789C front air dryer

2. Remote air supplyconnector

3. Engine oil quick fillconnector

• Engine oil (DEO CH-4)

- Higher temperaturecapability

- Better soot control

- Handles highersulfur fuels

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• 789C engine oil filters

1. Engine oil fill tube

2. Engine oil dipstick

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2

1

4

3

The engine oil filters (789C shown) are located on the left side of theengine. Engine oil should be added at the fill tube (1) and checked withthe dipstick (2). The 785C has three engine oil filters and is checked andfilled through the engine cover (see Slide No. 22).

On the 789C truck, engine oil samples can be taken at the Scheduled OilSampling (S•O•S) tap (3). (For the 785C truck, see Slide No. 10.)

The engine lubrication system is equipped with two oil pressure sensors (4). A sensor is located on each end of the oil filter base. Onesensor measures engine oil pressure before the filters. The other sensormeasures oil pressure after the filters. The sensors provide input signalsto the Engine Electronic Control Module (ECM). The ECM providesinput signals to the VIMS, which informs the operator of the engine oilpressure. Together, these sensors inform the operator if the engine oilfilters are restricted.

4. Engine oil pressuresensor

3. 789C engine oilS•O•S tap

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• Trapped engine oildrain (arrow)

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Shown is the 3512B engine used in the 785C truck. Three oil filters arelocated on the left side of the engine. The 3512B engine also has a fitting(arrow) that can be used to drain the engine oil that is trapped above thefilters. Do not add oil through the fitting (arrow) because unfiltered oilwill enter the engine. Any contamination could cause damage to theengine.

NOTICE

When changing the engine oil filters, drain the engine oil that istrapped above the oil filters through the fitting (arrow) to preventspilling the oil. Oil added to the engine through the fitting (arrow)will go directly to the main oil galleries without going through theengine oil filters. Adding oil to the engine through the fitting (arrow)may introduce contaminants into the system and cause damage to theengine.

- 30 -

1. High speed oilchange connector

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12

Engine oil can be added through a high speed oil change connector andwill enter the oil pan through the fitting (1).

An engine oil level switch (2) provides input signals to the Engine ECM.The Engine ECM provides an input signal to the VIMS, which informsthe operator of the engine oil level.

The oil level switch tells the operator when the engine oil level is low andit is unsafe to operate the truck without causing damage to the engine.The ENG OIL LEVEL LOW message is a Category 2 or 3 Warning.

2. Engine oil levelswitch

- 31 -

• Secondary fuel filters

1. Fuel priming pump

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2 1

The secondary fuel filters and the fuel priming pump (1) are locatedabove the engine oil filters on the left side of the engine. The fuelpriming pump is used to fill the filters after they are changed.

A fuel filter bypass switch (2) is located on the filter base. The bypassswitch provides an input signal to the Engine ECM. The Engine ECMsends the signal to the VIMS, which informs the operator if the filters arerestricted.

NOTE: If the fuel system requires priming, it may be necessary toblock the fuel return line during priming to force the fuel into theinjectors.

2. Fuel filter bypassswitch

- 32 -

1. Manual engineshutdown switch

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6

14

5

3

2

Before climbing the truck ladder, make sure that the manual engineshutdown switch (1) is OFF. The engine will not start if the manualshutdown switch is ON. If necessary, the switch can be used to stop theengine from the ground level. Operate the switch periodically to checkthe secondary steering system.

The toggle switches (2) control the lights in the engine compartment andabove the access ladder.

The RS-232 service connector (3) is used to connect a laptop computerwith VIMS PC software to upload new source and configuration files,view real time data or download logged information from the VIMS.

The battery disconnect switch (4) and VIMS service connector keyswitch (5) must be in the ON position before the laptop computer withVIMS software will communicate with the VIMS.

The blue service lamp (6) is part of the VIMS. When the key start switchis turned to the ON position, the VIMS runs through a self test. Duringthe self test, the service lamp will flash three times if any logged eventsare stored in the VIMS main module and once if no logged events arestored.

During normal operation, the service lamp will turn ON to notify servicepersonnel that the VIMS has an active data (machine) or maintenance(system) event. The service lamp flashes to indicate when an event isconsidered abusive to the machine.

2. Engine and accessladder light switches

3. RS-232 connector forVIMS

4. Battery disconnectswitch

5. Key switch for VIMSservice connector

6. VIMS service lamp

- 33 -

• 789C truck

• Inspect radiator

1. Air filter restrictionindicators

2. Dust valves

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1

2

Shown is the 789C truck. While climbing the ladder, make a thoroughinspection of the radiator. Be sure that no debris or dirt is trapped in thecores. Check the air filter restriction indicators (1) located on both sidesof the truck. If the yellow pistons are in the red zone (indicating that thefilters are plugged), the air filters must be serviced. Check the dustvalves (2) for plugging. If necessary, disconnect the clamp and open thecover for additional cleaning. Replace the dust valve if the rubber is notflexible.

The VIMS will also provide the operator with an air filter restrictionwarning when the filter restriction is approximately 6.2 kPa (25 in. of water). Black exhaust smoke is also an indication of air filterrestriction.

Two filter elements are installed in the filter housings. The large elementis the primary element and the small element is the secondary element.Air intake system tips:

- The primary element can be cleaned a maximum of six times.

- Never clean the secondary element for reuse. Always replace thesecondary element.

- Air filter restriction causes black exhaust smoke and low power.

- A 0.6°C (1°F) increase in intake temperature increases exhausttemperature 1.8°C (3°F).

- For every 250 mm (10 in.) of water restriction above 500 mm (20 in.) of water in an air filter, the inlet temperature increases 60°C(100°F).

- Exhaust temperature should not exceed 750°C (1382°F).

• Large primary element

• Small secondaryelement

- 34 -

• 789C cooling systemcapacity increased

1. Engine coolant shunttank

• Engine coolingsystems:

- Jacket water coolingsystem

- Aftercooler coolingsystem

2. Coolant level gauges

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2

1

Shown is a 789C truck. The capacity of the 789C cooling system hasbeen increased by 40% from 474 Liters (125 gal.) to 663 Liters (175 gal.).The radiator is larger and a shunt tank (1) has been added above theradiator.

The cooling system on the "C" Series trucks is divided into two systems.The two systems are the jacket water cooling system and the aftercoolercooling system. These two systems are not connected. When servicingthe cooling systems, be sure to drain and fill both systems separately.

The coolant levels are checked at the shunt tank. Use the gauges (2) ontop of the shunt tank to check the two coolant levels.

The water used in the cooling system is critical for good cooling systemperformance. Use distilled or deionized water whenever possible toprevent acids or scale deposits in the cooling system. Acids and scaledeposits result from contaminants that are found in most common watersources.

Never use water alone. All water is corrosive at engine operatingtemperatures without coolant additives. Also, water alone has none of thelubrication properties which are required for water pump seals.

• Use distilled water

• Never use water alone

- 35 -STMG 70611/98

The "C" Series trucks are filled at the factory with Extended Life Coolant(ELC). If ELC is maintained in the radiator, it is not necessary to use asupplemental coolant additive. If more than 10% of conventional coolantis mixed with the ELC, a supplemental coolant additive is required.

With conventional coolant, maintain a 3 to 6% concentration ofsupplemental coolant additive.

- Too much additive will form insoluble salts that cause water pumpseal wear, plugging and will coat parts with excessive deposits thatprevent heat transfer.

- Not enough additive will result in severe cavitation erosion whichwill pit and corrode cylinder liner and block surfaces.

- Use the 4C9301 Test Kit to measure the concentration of thesupplemental coolant additive in the cooling system.

Maintain a 30 to 60% concentration of Caterpillar Antifreeze.- More than 60% antifreeze concentration will reduce freeze

protection and cause radiator plugging.

- Less than 30% antifreeze concentration will result in cavitationerosion, which will pit and corrode cylinder liner and block surfacesand decrease water pump life.

- Most commercial antifreezes are formulated with high silicatecontent for gasoline engines and are not recommended for dieselengines.

The engine should operate between 88 and 99°C (190 and 210°F).

- Operating below this temperature range will cause overcoolingproblems.

- Operating above this temperature range will cause overheatingproblems.

Cooling system pressure should be between 55 and 110 kPa (8 and 16 psi).

- Raising the pressure raises the boiling point. If the pressure isinadequate, the coolant will boil over and the engine will overheat.

Do not fill the cooling system faster than 20 L/min. (5 gpm).- Filling the cooling system faster than 20 L/min. (5 gpm) will cause

air pockets that could produce damaging steam.

Keep the fan belts adjusted.

Keep the radiator cooling fins straight and clean.

• Conventional coolant:

- Maintain 3 to 6%concentration ofsupplementalcoolant additive

• Maintain 30 to 60%antifreezeconcentration

• Maintain correctoperating temperature

• Maintain correctcooling systempressure

• Trucks are filled withExtended Life Coolant(ELC)

• Do not fill coolingsystem too fast

• Adjust fan belts

• Keep radiator finsstraight and clean

- 36 -

• 785C truck

1. Air cleaner indicators

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2

1

Shown is a 785C truck. The air cleaner indicators (1) are located abovethe radiator next to the air filter screens. If the yellow pistons are in thered zone (indicating that the filters are plugged), the air cleaners must beserviced.

The coolant levels are checked at the radiator top tank. Use thegauges (2) on top of the radiator to check the two coolant levels.


- 37 -

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The ether cylinders (arrow) are located in the engine compartment behindthe radiator. Make sure the ether cylinders are not empty.

The Engine ECM will automatically inject ether from the ether cylindersduring cranking. The duration of automatic ether injection depends on thejacket water coolant temperature. The duration will vary from 10 to 130 seconds.

The operator can also inject ether manually with the ether switch in thecab on the center console (see Slide No. 48). The manual ether injectionduration is 5 seconds.

Ether will be injected only if the engine coolant temperature is below10°C (50°F) and engine speed is below 1900 rpm.

Ether starting tip:

- Cold weather causes rough combustion and white exhaust smokefrom unburned fuel. Ether injection will reduce the duration andseverity of unburned fuel symptoms.

• Ether cylinders(arrow)

• Automatic etherinjection

• Manual ether injection

- 38 -

• Batteries

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The batteries are located below the access panel on the right platform.Inspect the battery connections for corrosion or damage. Keep the batteryterminals clean and coated with petroleum jelly.

Inspect the electrolyte level in each battery cell, except for maintenancefree batteries. Maintain the level to the bottom of the fill openings withdistilled water.

Batteries give off flammable fumes that can explode resulting inpersonal injury.

Prevent sparks near batteries. They could cause vapors to explode.

Do not allow jumper cable ends to contact each other or the machine.

Do not smoke when checking battery electrolyte levels. Electrolyte isan acid and can cause personal injury if it contacts skin or eyes.

Always wear eye protection when starting a machine with jumpercables.

Always connect the battery positive (+) to battery positive (+) and thebattery negative (-) to the stalled machine frame (-).

WARNING

- 39 -

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2 3

1

Located on the right platform are the automatic lubrication system greasetank (1), the main air system tank (2) and the steering system tank (3).

Check the level of the grease in the automatic lubrication system tankwith the grease level indicator located on top of the tank.

A drain valve is located at the bottom right of the main air system tank.Drain the condensation from the air tank each morning.

1. Automatic lubricationtank

2. Main air system tank

3. Steering system tank

- 40 -

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6

3

1

2

5

4

The oil level for the steering system tank is checked at the upper sightgauge (1) when the oil is cold and the engine is stopped. After the engineis started, the oil level will decrease as the oil fills the steeringaccumulators.

After the accumulators are filled, the oil level should be checked again atthe lower sight gauge (2). When the engine is running and theaccumulators are fully charged, the oil level should not be below theENGINE RUNNING marking of the lower gauge. If the ENGINERUNNING level is not correct, check the nitrogen charge in eachaccumulator. A low nitrogen charge will allow excess oil to be stored inthe accumulators and will reduce the secondary steering capacity.

Before removing the cap to add oil to the steering system, be sure that theengine was shut off with the key start switch, and the steering oil hasreturned to the tank from the accumulators. Then, depress the pressurerelease button (3) on the breather to release any remaining pressure fromthe tank.

Also located on the tank are the main steering oil filter (4) and thesteering pump case drain filter (5).

1. Steering ENGINESTOPPED oil level

2. Steering ENGINERUNNING oil level

4. Main steering oil filter

5. Steering pump casedrain filter

3. Steering tankpressure releasebutton

- 41 -STMG 70611/98

If the steering pump fails or if the engine cannot be started, the connector (6) is used to attach an Auxiliary Power Unit (APU). The APUwill provide supply oil from the steering tank at the connector (6) tocharge the steering accumulators. Steering capability is then available totow the truck.

INSTRUCTOR NOTE: For more detailed information on servicingthe steering accumulators, refer to the Special Instruction "Repair of4T8719 Bladder Accumulator Group" (Form SEHS8757). For moreinformation on using the APU, refer to the Special Instructions"Using 1U5000 Auxiliary Power Unit (APU)"(Form SEHS8715) and"Using the 1U5525 Attachment Group" (Form SEHS8880).

6. APU supplementalsteering connector

- 42 -

• Parking/secondarybrake air tank drainvalve (arrow)

33

STMG 70611/98

Another small air tank (not visible) is located behind the cab (see SlideNo. 178). The air tank behind the cab supplies air to the parking andsecondary brakes. Drain the moisture from the tank daily with the drainvalve (arrow).

- 43 -

1. Windshield washerreservoir

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2

1

The windshield washer reservoir (1) is located in the compartment infront of the cab. Keep the reservoir full of windshield washer fluid.

The air conditioner filter (2) is also located in the compartment in front ofthe cab. Clean or replace the filter element when a reduction ofcirculation in the cab is noticed.

2. Air conditioner filter

- 44 -

35

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The remaining 10 Hours or Daily checks are performed in the operator'scompartment:

- Brakes: Check operation

- Indicators and gauges: Test operation

- Seat belt: Inspect

- Back-up alarm: Test operation

- Secondary steering: Test operation

The brakes are checked by engaging one of the brake systems and placingthe shift lever in FIRST FORWARD. Accelerate the engine until thetruck moves. The truck must not move below 1200 rpm. This procedureshould be repeated for each brake lever or pedal.

The cab fresh air filter is located behind the cover (arrow). Clean orreplace the cab fresh air filter when necessary.

INSTRUCTOR NOTE: Refer to the Operation and MaintenanceManual for more information on the remaining tests performed inthe cab.

• 10 hours/daily checksperformed in the cab

• Cab fresh air filter(arrow)

- 45 -

36

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OPERATOR'S STATION

The operator's station for the "C" Series Off-highway Trucks has beenchanged to improve operator comfort and ergonomics. The "C" Seriescab now resembles the cab used on the smaller "D" Series Off-highwayTrucks.

• "C" Series cabresembles "D" Series

- 46 -

• Operator and trainerseats

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Shown is a view of the operator's seat and the trainer's seat. The seats aremore comfortable with improved seat adjustments.

The trainer's seat has more leg room and can be replaced with anattachment air suspension seat.

- 47 -

• Hoist control lever(arrow)

• Electronicallycontrolled hoist

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The "C" Series truck hoist system is electronically controlled. The hoistcontrol lever (arrow) activates the four positions of the hoist controlvalve. The four positions are: RAISE, HOLD, FLOAT and LOWER.

A fifth position of the hoist valve is called the SNUB position. Theoperator does not have control over the SNUB position. The bodyposition sensor (see Slide No. 129) controls the SNUB position of thehoist valve. When the body is lowered, just before the body contacts theframe, the Transmission/Chassis ECM signals the hoist solenoids to movethe hoist valve spool to the SNUB position. In the SNUB position, thebody float speed is reduced to prevent hard contact of the body with theframe.

The truck should normally be operated with the hoist lever in the FLOATposition. Traveling with the hoist in the FLOAT position will make surethe weight of the body is on the frame and body pads and not on the hoistcylinders. The hoist valve will actually be in the SNUB position.

If the transmission is in REVERSE when the body is being raised, thehoist lever sensor is used to shift the transmission to NEUTRAL. Thetransmission will remain in NEUTRAL until:

1. The hoist lever is moved into the HOLD or FLOAT position; and

2. the shift lever has been cycled into and out of NEUTRAL.

NOTE: If the truck is started with the body raised and the hoist leverin FLOAT, the lever must be moved into HOLD and then FLOATbefore the body will lower.

• Reverse inhibitoroperation

• Hoist lever in FLOATfor normal operation

• Hoist SNUB position

- 48 -

• Left side of dash

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Shown is an overall view of the dash from the left side of the cab. Someof the improvements are:

- Telescopic/tilt steering column for individual adjustment

- Intermittent wiper/washer, turn signal control and dimmer switch

- Enhanced instrument layout

- Backlit rocker switches

- Steering wheel mounted electric horn control

- 49 -

40

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1

3

4

2

The operator controls to the left of the steering column are:

- Telescopic/tilt steering column adjustment lever (1): Push fortelescoping and pull for tilt

- Intermittent wiper/washer, turn signal control and dimmer switch (2)

- Steering wheel mounted electric horn control (3)

- Cigarette lighter (4): The cigarette lighter socket receives a 12-Voltpower supply. This socket can be used as a power supply for 12-Volt appliances. Another 12-Volt power port is provided behindthe operator's seat.

1. Steering columnadjustment lever

2. Wiper/washer, turnsignal and dimmercontrol

3. Horn control

4. Cigarette lighter

- 50 -

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Shown is a closer view of the intermittent wiper/washer, turn signalcontrol and dimmer switch.

Windshield washer: Push the button at the end of the lever to activate theelectrically powered windshield washer.

Intermittent wiper switch (six positions):

- OFF (0)

- Intermittent position 1 (one bar)

- Intermittent position 2 (two bars)

- Intermittent position 3 (three bars)

- Low speed continuous wiper (I)

- High speed continuous wiper (II)

Dimmer switch: Pull the lever toward the operator for BRIGHT lights,and push the lever away from the operator for DIM lights.

Turn signals: Lift the lever for a RIGHT turn, and lower the lever for aLEFT turn.

• Windshield washer

• Dimmer switch

• Turn signals

• Intermittent wiper

- 51 -

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Located on the right side of the steering column is the manual retarderlever. The manual retarder lever is used to modulate engagement of theservice brakes on all four wheels. The retarder lever can control themodulation of the service brakes more precisely than the service brakepedal located on the cab floor.

Located on the dash to the right of the retarder lever are (from left toright):

- Key start switch

- Temperature variable knob

- Fan speed switch

• Retarder lever

• Key start switch

• Temperature knob

• Fan speed switch

- 52 -

43

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3

2

1

Located on the floor of the cab are:

- Secondary brake pedal (1): Used to modulate application of theparking brakes on all four wheels.

- Service brake pedal (2): Used to modulate engagement of theservice brakes on all four wheels. For more precise modulation ofthe service brakes, use the manual retarder lever on the right side ofthe steering column.

- Throttle pedal (3): A throttle position sensor is attached to thethrottle pedal. The throttle position sensor provides the throttleposition input signals to the Engine ECM.

The Engine ECM provides an elevated engine idle speed of 1300 rpmwhen the engine oil temperature is below 60°C (140°F). The rpm isgradually reduced to 1000 rpm between 60°C (140°F) and 71°C (160°F).When the temperature is above 71°C (160°F), the engine will idle atLOW IDLE (700 rpm).

Increasing the low idle speed helps prevent incomplete combustion andovercooling. To temporarily reduce the elevated idle speed, the operatorcan release the parking brake or depress the throttle momentarily, and theidle speed will decrease to LOW IDLE for 10 minutes.

1. Secondary brakepedal

2. Service brake pedal

3. Throttle pedal

• Elevated idle

- 53 -

1. Transmission shiftlever

2. Parking brake airvalve

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2

1

To the right of the operator's seat is the shift console. Located on the shiftconsole are the transmission shift lever (1) and the parking brake air valve (2).

The "C" Series truck transmissions have SIX speeds FORWARD andONE speed REVERSE. The top gear limit and body up gear limit areprogrammable through the Transmission/Chassis ECM. The top gearlimit can be changed from THIRD to SIXTH. The body up gear limit canbe changed from FIRST to THIRD.

• Top and body up gearlimits can bereprogrammed

- 54 -

• Overhead switches:

1. Hazard lights

2. Headlights andparking/taillights

3. Fog lights

4. Back-up lights

5. Front flood/ladderlights

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54321

Located in the overhead panel are several switches:

- Hazard lights (1)

- Headlights and parking/taillights (2)

- Fog lights (3)

- Back-up lights (4)

- Front flood/ladder lights (5)

- 55 -

46

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1

2

3

Shown is the circuit breaker panel located behind the operator's seat. Theprevious "B" Series trucks used fuses to protect many of the electricalcircuits. The "C" Series trucks use only circuit breakers to protect theelectrical circuits.

A 12-Volt/5 amp power port (1) provides a power supply for 12-Voltappliances, such as a laptop computer.

A laptop computer with the VIMS software installed can be connected tothe diagnostic connector (2) to obtain diagnostic and productioninformation from the VIMS Electronic Control.

A laptop computer with the Electronic Technician (ET) software installedcan be connected to the CAT Data Link connector (3) to obtain diagnosticinformation and perform programming functions on all the electroniccontrols.

3. CAT Data Linkconnector

1. Power port

• "C" Series trucks useonly circuit breakers

2. VIMS diagnosticconnector

- 56 -

• Center dash panel

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Shown is the center of the front dash panel. Eight dash indicators, thefour-gauge cluster module and the speedometer/tachometer module arevisible.

The four dash indicators to the left of the four-gauge cluster module are(from top to bottom):

- Left turn

- Body up: Lights when the body is up. Input is from the bodyposition sensor.

- Reverse: Lights when the shift lever switch is in REVERSE.

- High beam

• Left dash indicators(top to bottom):

- Left turn

- Body up

- Reverse

- High beam

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The four dash indicators to the right of the speedometer/tachometermodule are (from top to bottom):

- Right turn

- Action lamp: Lights when a Category 2, 2-S or Category 3 Warningis active.

- Retarder: Lights when the retarder is ENGAGED (Auto or Manual).Flashes rapidly when a fault in the ARC system is detected.

- TCS: Lights when the Traction Control System (TCS) isENGAGED.

The four systems monitored by the four-gauge cluster module are (top andbottom, left to right):

- Engine coolant temperature: Maximum operating temperature is107°C (225°F).

- Brake oil temperature: Maximum operating temperature is 121°C (250°F).

- System air pressure: Minimum operating pressure is450 kPa (65 psi).

- Fuel level: Minimum operating levels are 10% (Category 1) and 5% (Category 2).

The three systems monitored by the speedometer/tachometer module are:

- Tachometer: Displays the engine speed in rpm.

- Ground speed: Displayed in the left side of the three-digit displayarea and can be displayed in miles per hour (mph) or kilometers per hour (km/h).

- Actual gear: Displayed in the right side of the three-digit displayarea and consists of two digits that show the actual transmission gearthat is engaged. The left digit shows the actual gear (such as "1,""2," etc.). The right digit shows the direction selected ("F," "N" or"R").

• Right dash indicators(top to bottom):

- Right turn

- Action lamp

- Retarder

- TCS

• Four-gauge clustermodule:

- Engine coolanttemperature

- Brake oiltemperature

- System air pressure

- Fuel level

• Speed/Tach module:

- Tachometer

- Ground speed

- Actual gear

- 58 -

• Rocker switches(top row):

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To the right of the Speedometer/Tachometer Module are several rockerswitches. The rocker switches control the following systems:

Top row (from left to right)

- Throttle back-up: Raises the engine speed to 1300 rpm if the throttlesensor signal is invalid.

- Ether starting aid: Allows the operator to manually inject ether ifthe engine oil temperature is below 10°C (50°F) and engine speed isbelow 1900 rpm. The manual ether injection duration is fiveseconds (see Slides No. 66 and 90).

- ARC: Activates the Automatic Retarder Control (ARC) system.

- Brake release/hoist pilot: Used to release the parking brakes fortowing and provide hoist pilot oil to lower the body with a deadengine. The small latch must be pushed UP before the switch can bepushed DOWN.

- TCS test: Tests the Traction Control System (TCS). Use this switchwhen turning in a tight circle with the engine at LOW IDLE and thetransmission in FIRST GEAR. The brakes should ENGAGE andRELEASE repeatedly. The test must be performed while turning inboth directions to complete the test.

Bottom row (from left to right)

- Panel Lights: Use this switch to DIM the panel lights

- Air Conditioning: Use this switch to turn ON the air conditioner.

- Throttle back-up

- Ether starting aid

- ARC

- Brake release/hoistpilot

- TCS test

- Panel lights

- Air conditioning

• Rocker switches(bottom row):

- 59 -

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2

1

Shown is the Vital Information Management System (VIMS) messagecenter module (1) and the keypad (2).

The message center module consists of an alert indicator, a universalgauge and a message display window. The alert indicator flashes when aCategory 1, 2, 2-S or 3 Warning is present.

The universal gauge displays active or logged data (machine) andmaintenance (system) events. The universal gauge will also display thestatus of a parameter selected for viewing by depressing the GAUGE keyon the keypad.

The message display window shows various types of text information tothe operator.

• VIMS

1. Message centermodule:

- Alert indicator

- Universal gauge

- Message displaywindow

2. Keypad

- 60 -

• VIMS warningcategories

STMG 70611/98

The VIMS provides three Warning Categories. The first category requiresonly operator awareness. The second category states that the operation ofthe machine and the maintenance procedure of the machine must bechanged. The third Warning Category states that the machine must besafely shut down immediately.

Warning Category 1

For a Category 1 Warning, the alert indicator will flash. The universalgauge may display the parameter and a message will appear in themessage display window. A Category 1 Warning alerts the operator that amachine system requires attention. The "OK" key on the keypad can beused to acknowledge the warning. Some warnings will be silenced for apredetermined period. After this time period, if the abnormal condition isstill present, the warning will reappear.

Warning Category 2

For a Category 2 Warning, the alert indicator and the action lamp willflash. The universal gauge may display the parameter and a message willappear in the message display window. A Category 2 warning alerts theoperator that a change in machine operation is required to avoid possibledamage to the indicated system. The "OK" key on the keypad can beused to acknowledge the warning. Some warnings will be silenced for apredetermined period. After this time period, if the abnormal condition isstill present, the warning will reappear.

Warning Category 2-S

For a Category 2-S Warning, the alert indicator and the action lamp willflash and a continuous action alarm will sound, which indicate a SEVERECategory 2 Warning. The universal gauge may display the parameter anda message will appear in the message display window. A Category 2-SWarning alerts the operator to immediately change the operation of themachine to avoid possible damage to the indicated system. When thechange in operation is made to an acceptable condition, the action alarmwill turn off.

Warning Category 3

For a Category 3 Warning, the alert indicator and the action lamp willflash and the action alarm will sound intermittently. The universal gaugemay display the parameter and a message will appear in the messagedisplay window. A Category 3 Warning alerts the operator that themachine must be safely shut down immediately to avoid damage to themachine or prevent personal injury. Some Category 3 Warnings cannotbe stopped by pressing the "OK" key.

• Warning Category 1


• Warning Category 2-S


50

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• VIMS

TRANSMISSION/CHASSIS

ECM

ENGINEECM

SERVICELAMP

MESSAGECENTERMODULE

GAUGECLUSTERMODULE

KEYPADMODULE

SENSORS

VIMSINTERFACE

MODULE

VIMSINTERFACE

MODULE

SENSORS

VIMSSERVICE TOOL

ANDSOFTWARE

CAT DATA LINK

SERVICEKEY SWITCH

ACTIONLAMP

ACTIONALARM

ELECTRONICTECHNICIAN/ECAP

VIMS MAIN MODULE

DISPLAY DATA LINK

VIMSRS-232PORT

CAT DATA LINK

VITAL INFORMATIONMANAGEMENT SYSTEM

(VIMS)

SPEEDOMETER/TACHOMETER

MODULE

3F12 MPHkm/h

KEYPADDATA LINK

BRAKE ECM(ARC/TCS)

The VIMS uses two interface modules to receive input signals from manyswitches and sensors located around the machine. The VIMS alsocommunicates with other electronic controls on the machine. The VIMSprovides the operator and the service technician with a complete look atthe current and past conditions of all the systems on the truck.

If the truck is equipped with the VIMS, the Truck ProductionManagement System (TPMS) is an integral part of the VIMS. Access tothe TPMS information is provided through the VIMS message center andkeypad modules and a laptop computer with the VIMS PC softwareinstalled.

The VIMS monitors all the systems on the truck, but ET is used forprogramming, running diagnostic tests and retrieving logged informationfrom the Engine ECM, the Transmission/Chassis ECM, and the BrakeECM (ARC and TCS).

• ET required forprogramming anddiagnostics

• TPMS is part of VIMS

- 62 -

1. VIMS main module

2. VIMS interfacemodule No. 1

3. VIMS interfacemodule No. 2

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5

4

3

1

2

Located in the compartment at the rear of the cab are the VIMS MainModule (1), the VIMS Interface Module No. 1 (2) and the VIMS InterfaceModule No. 2 (3). These components make up the "heart" of the VIMS.

Also in this location are the Brake ECM (4) and the Transmission/ChassisECM (5).

The Brake ECM controls the Automatic Retarder Control (ARC) system,the Traction Control System (TCS) and rear axle cooling.

The Transmission/Chassis ECM controls the shifting of the transmission,torque converter lockup, the hoist system, the neutral-start feature, powertrain filter and temperature monitoring, and the automatic lubricationfeature.

All these electronic controls, along with the Engine ECM, communicatewith each other on the CAT Data Link. All the information from thesecontrols can be accessed through the VIMS message center or a laptopcomputer with Electronic Technician (ET) or VIMS PC software.

4. Brake ECM

5. Transmission/Chassis ECM

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• VIMS connector

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Shown is a laptop computer with the VIMS PC diagnostic softwareinstalled. The laptop computer is connected to the VIMS diagnosticconnector.

Some of the operations that can be performed with a laptop computer withVIMS PC installed are:

- View real time data (similar to the status menu of ET)

- View payload data

- Start and stop a data logger

- Calibrate the payload system

- Upload source and configuration files (similar to flash programmingother ECM’s with ET)

- Assign serial and equipment numbers

- Reset onboard date, time and hourmeter

- Download event list, data logger, event recorder, payload data, trenddata, cumulative data and histogram data

INSTRUCTOR NOTE: For more detailed information on the VIMS,refer to the Service Manual Module "Vital Information ManagementSystem (VIMS)" (Form SENR6059).

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• Electronic Technician(ET)

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Shown is the 7X1700 Communication Adapter and a laptop computerwith the Electronic Technician (ET) diagnostic software installed. Thecommunication adapter is connected to the CAT Data Link diagnosticconnector located on the circuit breaker panel.

The electronic controls (Transmission/Chassis ECM and Brake ECM)used on the "C" Series trucks no longer have diagnostic windows toaccess diagnostic information. To perform diagnostic and programmingfunctions with these electronic controls, the service technician must use alaptop computer with ET.

• ET must be used withelectronic controls

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• 3512B and 3516Bengines

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ENGINE

Shown is the 3516B engine used in the 789C Off-highway Truck. The789C is equipped with the Caterpillar 3516B quad turbocharged andaftercooled engine. The 785C is equipped with the Caterpillar 3512Btwin turbocharged and aftercooled engine.

The 785C and 789C engines have increased horsepower.

The engine power ratings for the 785C and 789C trucks are:

785C: gross power--1082 kW (1450 hp)net power--1007 kW (1350 flywheel hp)

789C: gross power--1417 kW (1900 hp)net power--1335 kW (1790 flywheel hp)

These engines utilize the Electronic Unit Injection (EUI) system forpower, reliability and economy with reduced sound levels and lowemissions.

• Engine power ratings

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• 3500B electroniccontrol systemcomponent diagram

A/C PRESSURESWITCH

CRANKCASEPRESSURE

GROUND LEVELSHUTDOWN SWITCH

FUEL FILTERSWITCH

PRE-LUBRICATION RELAY

OIL LEVELSWITCH (LOW)

OIL LEVELSWITCH (ADD)

FANFAN SPEED SENSOR

FAN CLUTCHSOLENOID

SERVICE TOOL

CAT DATA LINK

ENGINE COOLANT TEMPERATURE

ENGINEECM

GROUNDBOLT

15 AMPBREAKER

MAINPOWER RELAY

KEY STARTSWITCH

SPEED/TIMING SENSOR

ENGINE OIL PRESSURE(UNFILTERED)

COOLANT FLOW SWITCH

TIMING PROBECONNECTOR

ETHER SOLENOID

DISCONNECT SWITCH

3500B ELECTRONIC CONTROL SYSTEMCOMPONENT DIAGRAM

ELECTRONIC UNITINJECTORS

TURBO OUTLET PRESSURE (BOOST)

RIGHT TURBO INLET PRESSURE

ATMOSPHERIC PRESSURE

ENGINE OIL PRESSURE (FILTERED)

THROTTLE

ENGINE OILRENEWAL SOLENOID

SHUTTER SOLENOID

REAR AFTERCOOLER TEMPERATURE

LEFT TURBO INLET PRESSURE

RIGHT TURBO EXHAUST

LEFT TURBO EXHAUST

THROTTLE OVERRIDE SWITCHMANUAL ETHERSWITCH

EXHAUSTWASTEGATESOLENOID

24 V

TRANSMISSION/CHASSIS ECM

BRAKE ECMVIMS

Engine Electronic Control System

Shown is the electronic control system component diagram for the 3500Bengines used in the "C" Series trucks. Fuel injection is controlled by theEngine Electronic Control Module (ECM).

Many electronic signals are sent to the Engine ECM by sensors, switchesand senders. The Engine ECM analyzes these signals and determineswhen and for how long to energize the injector solenoids.

When the injector solenoids are energized determines the timing of theengine. How long the solenoids are energized determines the enginespeed.

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The Engine ECM will provide a "Pull-up Voltage" to the signal circuit ofmost sensors when the ECM senses an OPEN circuit. Frequency sensorsdo not receive a Pull-up Voltage. The signal circuit is usually Pin C of the3-pin sensor connectors. The Pull-up Voltage for most sensors isapproximately 6.50 Volts, but this value can vary with different electroniccontrols. Generally, the Pull-up Voltage will be higher than the high valueof a sensor's normal range. For example, the normal range of a coolanttemperature sensor is 0.4 to 4.6 Volts with temperatures between -40°C and +120°C (-40°F and +248°F). The Pull-up Voltage of 6.50 Volts for this sensor is greater than the normal 4.6 Volts high value.

To test for Pull-up Voltage, use a digital multimeter set to "DC Voltage,"and use the following procedure (key start switch must be ON):

1. Measure between Pin B (analog or digital return) and Pin C (signal) onthe ECM side of a sensor connector before it is disconnected. Thevoltage that is associated with the current temperature or pressureshould be shown.

2. Disconnect the sensor connector while still measuring the voltagebetween Pins B and C. If the circuit between the ECM and the sensorconnector is good, the multimeter will display the Pull-up Voltage.

• Pull-up Voltage

• Pull-up Voltage test

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• Engine ECM (arrow)

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Fuel injection and some other systems are controlled by the Engine ECM(arrow) located on top of the engine. Other systems controlled by theEngine ECM include:

- Ether injection - Engine start function

- Engine oil pre-lubrication - Variable speed fan control

The Engine ECM has two 40-pin connectors. The connectors areidentified as "J1" and "J2." Be sure to identify which connector is the J1or J2 connector before performing diagnostic tests.

The Engine ECM is cooled by fuel. Fuel flows from the fuel transferpump through the ECM to the secondary fuel filters.

Occasionally, Caterpillar will make changes to the internal software(personality module) that controls the performance of the engine. Thesechanges can be performed by physically installing a new personalitymodule, located below the ECM, or by using the WinFlash program thatis part of the laptop software program, Electronic Technician (ET). ET isused to diagnose and program the electronic controls used in Off-highwayTrucks. If using the WinFlash program, a "flash" file must be obtainedfrom Caterpillar and uploaded into the existing ECM personality module.

The ECM in earlier 3500 engines had one 70-pin connector and cannot bereprogrammed with the WinFlash application in ET. Reprogramming ofthe earlier ECM requires a replacement of the personality module locatedbehind an access cover on the ECM.

• ECM cooled by fuel

• Personality modulesand flash files

- Controls fuelinjection

- Controls othersystems

- Has two 40-pinconnectors

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• Timing calibrationconnector

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A timing calibration connector is located next to the ECM. If the enginerequires timing calibration, a timing calibration sensor (magnetic pickup)is installed in the flywheel housing and connected to the timingcalibration connector.

Using the Caterpillar ET service tool, timing calibration is performedautomatically for the speed/timing sensors. The desired engine speed isset to 800 rpm. This step is performed to avoid instability and ensuresthat no backlash is present in the timing gears during the calibrationprocess.

Timing calibration improves fuel injection accuracy by correcting for anyslight tolerances between the crankshaft, timing gears and timing wheel.

Timing calibration is normally performed after the following procedures:

1. ECM replacement

2. Speed/timing sensor replacement

3. Timing wheel replacement

INSTRUCTOR NOTE: Some of the engine electronic control systeminput components are shown during the discussion of other systems.See the following slide numbers:

25. Engine shutdown switch46. CAT Data Link connector48. Throttle back-up switch48. Manual ether switch62. Air conditioner compressor pressure switch63. Engine crankcase pressure sensor68. Coolant temperature sensor68. Turbocharger outlet pressure sensor68. Engine fan speed sensor70. Engine oil level switch74. Coolant flow switch78. Rear aftercooler temperature sensor81. Engine oil pressure and filter restriction sensors86. Fuel filter restriction switch90. Turbocharger inlet pressure sensor92. Turbocharger temperature sensor

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The atmospheric pressure sensor (arrow) is located adjacent to the EngineECM. The Engine ECM uses the atmospheric pressure sensor as areference for calculating boost and air filter restriction.

The sensor is also used for derating the engine at high altitudes. TheECM will derate the engine at a rate of 1% per kPa to a maximum of20%. Derating begins at a specific elevation. The elevation specificationcan be found in the Technical Marketing Information (TMI) located onthe Caterpillar Network. If the Engine ECM detects an atmosphericpressure sensor fault, the ECM will derate the fuel delivery to 20%. If theEngine ECM detects an atmospheric and turbocharger inlet pressuresensor fault at the same time, the ECM will derate the engine to themaximum rate of 40%.

The Engine ECM also uses the atmospheric pressure sensor as a referencewhen calibrating all the pressure sensors.

The atmospheric pressure sensor is one of the many analog sensors thatreceive a regulated 5.0 ± .0.5 Volts from the Engine ECM. Theatmospheric pressure sensor output signal is a DC Voltage output signalthat varies between 0.2 and 4.8 Volts DC with an operating pressure rangebetween 0 and 111 kPa (0 and 15.7 psi).

To check the output signal of analog sensors, connect a multimeterbetween Pins B and C of the sensor connector. Set the meter to read "DC Volts." The DC Voltage output of the atmospheric pressure sensorshould be between 0.2 and 4.8 Volts DC.

• Atmospheric pressuresensor (arrow)

• High altitude derate

• Check atmosphericpressure sensoroutput signal

• Atmospheric pressuresensor signal is DCVolts

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1. Engine speed/timingsensor

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2

1

The engine speed/timing sensor (1) is positioned near the rear of the leftcamshaft. The sensor signals the speed, direction and position of thecamshaft by counting the teeth and measuring the gaps between the teethon the timing wheel which is mounted on the camshaft.

The engine speed/timing sensor is one of the most important inputs to theEngine ECM. If the Engine ECM does not receive an input signal fromthe engine speed/timing sensor, the engine will not run.

The engine speed/timing sensor receives a regulated 12.5 ± 1.0 Volts fromthe Engine ECM. To check the output signal of the speed/timing sensor,connect a multimeter between Pins B and C of the speed/timing sensorconnector. Set the meter to read "Frequency." The frequency output ofthe speed/timing sensor should be approximately:

- Cranking: 23 to 40 Hz

- Low Idle: 140 Hz

- High Idle: 385 Hz

A passive (two wire) engine speed sensor (2) is positioned on top of theflywheel housing. The passive speed sensor uses the passing teeth of theflywheel to provide a frequency output. The passive speed sensor sendsthe engine speed signal to the Transmission/Chassis ECM and the BrakeECM.

• Check speed/timingsensor output signal

• No speed/timingsensor signalprevents operation

2. Engine speed sensor

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The signal from the passive speed sensor is used for several purposes:

- Torque converter lockup clutch slippage monitoring

- Transmission clutch slippage monitoring

- Automatic Retarder Control (ARC) engine control speed

The output signal of the passive speed sensor can also be checked byconnecting a multimeter between the two pins of the speed sensorconnector and setting the meter to read frequency.

NOTE: Turn ON the engine shutdown switch (see Slide No. 25)during the cranking test to prevent the engine from starting. Thecranking speed and frequency output will vary depending on weatherand machine conditions. When viewing engine speed in the ET statusscreen, cranking speed should be between 100 and 250 rpm.

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The throttle position sensor (arrow) provides the desired throttle positionto the Engine ECM. If the Engine ECM detects a fault in the throttleposition sensor, the throttle back-up switch (see Slide No. 48) can be usedto increase the engine speed to 1300 rpm.

The throttle position sensor receives a regulated 8.0 ± 0.5 Volts from theEngine ECM. The throttle position sensor output signal is a Pulse WidthModulated (PWM) signal that varies with throttle position and isexpressed as a percentage between 0 and 100%.

To check the output signal of the throttle position sensor, connect amultimeter between Pins B and C of the throttle position sensorconnector. Set the meter to read "Duty Cycle." The duty cycle output ofthe throttle position sensor should be:

- Low Idle: 16 ± 6%

- High Idle: 85 ± 4%

• Check throttleposition sensoroutput signal

• Throttle positionsensor signal is PWM

• Throttle positionsensor (arrow)

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• EUI fuel injectorsolenoid (arrow)

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Shown is the top of a cylinder head with the valve cover removed. Themost important output from the Engine ECM is the Electronic UnitInjection (EUI) injector solenoid (arrow). One injector is located in eachcylinder head. The engine control analyzes all the inputs and sends asignal to the injector solenoid to control engine timing and speed.

Engine timing is determined by controlling the start and end time that theinjector solenoid is energized. Engine speed is determined by controllingthe duration that the injector solenoid is energized.

3500B injectors are calibrated during manufacturing for precise injectiontiming and fuel discharge. After the calibration, a four-digit "E-trim"code number is etched on the injector tappet surface. The E-trim codeidentifies the injector's performance range.

When the injectors are installed into an engine, the trim code number ofeach injector is entered into the personality module (software) of theEngine ECM using the ECAP or ET service tool. The software uses thetrim code to compensate for the manufacturing variations in the injectorsand allows each injector to perform as a nominal injector.

When an injector is serviced, the new injector's trim code should beprogrammed into the Engine ECM. If the new trim code is not entered,the previous injector's characteristics are used. The engine will not beharmed if the new code is not entered, but the engine will not providepeak performance.

• Engine timing andspeed

• E-trim code numberidentifies injectorperformance range

• Trim code numbersare programmed intoEngine ECM

• Enter new trim codesduring injector service

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• 3500B improvements

3500B IMPROVEMENTSINPUT SWITCHES AND SENSORS

• COOLANT FLOW

• REAR AFTERCOOLER TEMPERATURE

• ENGINE OIL LEVEL

• TURBOCHARGER TEMPERATURE

• ENGINE OIL FILTER PRESSURE/RESTRICTION

• ENGINE FAN SPEED

• FUEL FILTER RESTRICTION

• AIR CONDITIONER COMPRESSOR PRESSURE

• CRANKCASE PRESSURE

The 3500B engines have many improvements over the original 3500engines. Some of the improvements are accomplished by addingadditional switch and sensor inputs to the Engine ECM. Addingadditional inputs allows the ECM to control the engine more precisely.Additional inputs to the 3500B ECM are:

- Coolant flow is monitored (see Slide No. 74).

- Rear aftercooler temperature is measured (see Slide No. 78).

- Engine oil level is monitored (see Slide No. 70).

- Two turbocharger temperature sensors measure exhaust temperatures(see Slide No. 92).

- Two engine oil pressure sensors are located on the oil filter base tomeasure oil pressure and oil filter restriction (see Slides No. 81 and82).

- Engine fan speed is measured (with variable fan speed attachment).

- Fuel filter restriction is monitored (see Slide No. 86).

- Air conditioner compressor pressure is monitored (for variable fanspeed control) (see Slide No. 62).

- Engine crankcase pressure is measured (see Slide No. 63).

• Additional inputs

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An air conditioner compressor switch (arrow) is located at the rear of theair conditioner compressor. If the truck is equipped with the variable fanspeed attachment, the air conditioner compressor switch signals theEngine ECM when the air conditioner system is ON. When the airconditioner system is ON, the ECM sets the variable speed fan atMAXIMUM rpm.

Disconnecting the air conditioner compressor switch will also signal theECM to set the fan speed at MAXIMUM rpm.

• Air conditionercompressor switch(arrow)

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• Crankcase pressuresensor (arrow)

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The crankcase pressure sensor (arrow) is located on the right side of theengine above the engine oil cooler. The crankcase pressure sensorprovides an input signal to the Engine ECM. The ECM provides thesignal to the VIMS, which informs the operator of the crankcase pressure.

High crankcase pressure may be caused by worn piston rings or cylinderliners.

If crankcase pressure exceeds 3.6 kPa (.5 psi) or 14.4 inches of water, ahigh crankcase pressure event will be logged. No factory password isrequired to clear this event.

• Crankcase pressureevent

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3500B IMPROVEMENTSPREVIOUS LOGGED EVENTS

• AIR FILTER RESTRICTION

• LOW OIL PRESSURE

• HIGH COOLANT TEMPERATURE

• ENGINE OVERSPEED

The 3500B ECM logs the four events of the previous 3500 engine plussome additional events. The four events logged by the 3500 ECM and the3500B ECM are:

Air filter restriction: Greater than 6.25 kPa (25 in. of water). Maximumderate of 20%.

If the atmospheric and turbo inlet pressure sensors both fail at the sametime, a derate of 40% will occur.

Low oil pressure: From less than 44 kPa (6.4 psi) at LOW IDLE to lessthan 250 kPa (36 psi) at HIGH IDLE.

High coolant temperature: Greater than 107°C (226°F).

Engine overspeed: Greater than 2200 rpm.

NOTE: Factory passwords are required to clear all the events listedabove.

• Events logged by ECM

• 40% derate with twosensor failures

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• Additional loggedevents

3500B IMPROVEMENTSADDITIONAL LOGGED EVENTS

• OIL FILTER RESTRICTION • LOW COOLANT FLOW

• FUEL FILTER RESTRICTION • USER DEFINED SHUTDOWN

• HIGH EXHAUST TEMPERATURE • LOW BOOST PRESSURE

• HIGH AFTERCOOLER TEMPERATURE • HIGH BOOST PRESSURE

• ENGINE OIL LEVEL LOW • PRE-LUBE OVERRIDE

• HIGH CRANKCASE PRESSURE

Additional events logged by the 3500B ECM are:

Oil filter restriction: Greater than 70 kPa (10 psi), no factory passwordrequired. Greater than 200 kPa (29 psi), factory password required.

Fuel filter restriction: Greater than 138 kPa (20 psi). No factorypassword required.

Exhaust temperature high: Greater than 750°C (1382°F). Maximumderate of 20%. Factory password required.

Aftercooler coolant temperature high: Greater than 107°C (226°F).Factory password required.

Engine oil level low: No factory password required.

Crankcase pressure high: Greater than 3.6 kPa (.5 psi) or 14.4 inches ofwater. No factory password required.

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Coolant flow low: Factory password required.

User defined shutdown: The customer has the option of installingsystems (fire suppression) that will shut down the engine if desired. If theinstalled system sends a ground signal to the Engine ECM at ConnectorJ1 Pin 19, a user defined shutdown will occur. Factory passwordrequired.

The VIMS will shut down the engine for any of the following conditions:

- Engine oil level low

- Engine oil pressure low

- Engine coolant temperature high

- Engine coolant level low

- Aftercooler coolant level low

The engine will shut down only when the ground speed is zero and theparking brake is ENGAGED. Factory password required.

Boost pressure low: 35 kPa (5 psi) lower than desired. Maximum derateof 10%. No factory password required.

Boost pressure high: 20 kPa (3 psi) greater than desired. Maximumderate of 10%. No factory password required.

Pre-lube override: Override the engine oil pre-lubrication system withthe key start switch. Factory password required. (see Slide No. 67)

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3500B IMPROVEMENTSSYSTEMS CONTROLLED BY ECM

• ETHER INJECTION

• RADIATOR SHUTTER CONTROL

• COLD MODE

• COLD CYLINDER CUTOUT

• ENGINE START FUNCTION

• ENGINE OIL PRE-LUBRICATION

• VARIABLE SPEED FAN CONTROL

• ENGINE OIL RENEWAL SYSTEM

The Engine ECM also regulates other systems by energizing solenoids orrelays. Some of the other systems controlled by the ECM are:

Ether Injection: The Engine ECM will automatically inject ether fromthe ether cylinders during cranking. The duration of automatic etherinjection depends on the jacket water coolant temperature. The durationwill vary from 10 to 130 seconds. The operator can also inject ethermanually with the ether switch in the cab on the center console (see SlideNo. 48). The manual ether injection duration is 5 seconds. Ether will beinjected only if the engine coolant temperature is below 10°C (50°F) andengine speed is below 1900 rpm.

Radiator Shutter Control: On trucks that operate in cold weather,shutters can be added in front of the radiator. Installing shutters in front ofthe radiator allows the engine to warm up to operating temperaturequicker. If a truck is equipped with the attachment radiator shuttercontrol, the shutters are controlled by the Engine ECM.

• Engine ECM controlsother systems

• Ether injection

• Radiator shuttercontrol

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Cold Mode: The Engine ECM provides an elevated engine idle speed of1300 rpm when the engine oil temperature is below 60°C (140°F). Therpm is gradually reduced to 1000 rpm between 60°C (140°F) and 71°C(160°F). When the temperature is greater than 71°C (160°F), the enginewill operate at low idle (700 rpm).

Increasing the low idle speed helps prevent incomplete combustion andovercooling. To temporarily reduce the elevated idle speed, the operatorcan release the parking brake or depress the throttle momentarily, and theidle speed will decrease to LOW IDLE for 10 minutes.

Cold Cylinder Cutout: The 3500B engine uses a cold cylinder cutoutfunction to:

- Reduce white exhaust smoke (unburned fuel) after start-up andduring extended idling in cold weather

- Minimize the time in Cold Mode

- Reduce the use of ether injection.

After the engine is started and the automatic ether injection system hasstopped injecting ether, the Engine ECM will cut out one cylinder at atime to determine which cylinders are firing. The ECM will disable someof the cylinders that are not firing.

The ECM can identify a cylinder which is not firing by monitoring thefuel rate and engine speed during a cylinder cutout. The ECM averagesthe fuel delivery and analyzes the fuel rate change during a cylindercutout to determine if the cylinder is firing.

Disabling some of the cylinders during Cold Mode operation will causethe engine to run rough until the temperature increases above the ColdMode temperature. This condition is normal, but the operator should beaware it exists to prevent unnecessary complaints.

Engine Start Function: The Engine Start function is controlled by theEngine ECM and the Transmission/Chassis ECM. The Engine ECMprovides signals to the Transmission/Chassis ECM regarding the enginespeed and the condition of the engine pre-lubrication system. TheTransmission/Chassis ECM will energize the starter relay only when:

- The shift lever is in NEUTRAL.

- The parking brake is ENGAGED.

- The engine speed is zero rpm.

- The engine pre-lubrication cycle is complete or turned OFF.

NOTE: To protect the starter, the starter is disengaged when theengine rpm is above 300 rpm.

• Cold cylinder cutout

• Cold mode

• Engine runs roughduring Cold Mode

• Engine start function

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21

Engine Oil Pre-lubrication: Engine oil pre-lubrication is controlled bythe Engine ECM and Transmission/Chassis ECM. TheTransmission/Chassis ECM signals the Engine ECM when to energize thepre-lubrication pump relay (1). The Engine ECM signals theTransmission/Chassis ECM to crank the engine when:

- Engine oil pressure is 3 kPa (.4 psi) or higher.

- The pre-lubrication pump (2) has run for 17 seconds. (If the systemtimes out after 17 seconds, a pre-lubrication time out fault is loggedin the Engine ECM.)

- The engine has been running in the last two minutes.

- Coolant temperature is above 50°C (122°F).

The engine oil pre-lubrication system can be bypassed to allow quickstarts. To override the pre-lubrication system, turn the key start switch tothe CRANK position for a minimum of two seconds. TheTransmission/Chassis ECM will begin the pre-lube cycle. While the pre-lube cycle is active, turn the key start switch to the OFF position. Within10 seconds, turn the key start switch back to the CRANK position. TheTransmission/Chassis ECM will energize the starter relay.

If the engine oil pre-lubrication system is bypassed using the aboveprocedure, the Engine ECM will log a pre-lube override event thatrequires a factory password to clear.

NOTE: The ECAP and ET can enable or disable the pre-lubricationfeature in the Engine ECM.

• Engine oilpre-lubrication

1. Pre-lubrication pumprelay

2. Pre-lubrication pump

• Pre-lubricationoverride

• Pre-lubricationoverride event

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• Variable speed fancontrol:

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1

2

3

Variable Speed Fan Control: If the engine is equipped with a variablespeed fan, the Engine ECM regulates the fan speed. Fan speed variesaccording to the temperature of the engine. The ECM sends a signal tothe variable speed fan control solenoid valve (1) and engine oil pressureengages a clutch as needed to change the speed of the fan.

The jacket water coolant temperature sensor (2) is located in the jacketwater temperature regulator (thermostat) housing. The ECM uses thecoolant temperature sensor information as the main parameter to controlthe fan speed. The aftercooler temperature sensor, air conditionerpressure sensor and brake cooling oil temperature sensors are also used asinputs to determine the required fan speed. A speed sensor (not shown) islocated behind the fan pulley and informs the ECM of the current fanspeed.

The variable speed fan feature can be turned off using the ECAP or ETservice tool. Turning off the variable speed fan feature will set the fanspeed at MAXIMUM rpm. Disconnecting the air conditioningcompressor switch will also signal the ECM to set the fan speed atMAXIMUM rpm (see Slide No. 62).

The turbocharger outlet pressure sensor (3) sends an input signal to theEngine ECM. The ECM compares the value of the turbo outlet pressuresensor with the value of the atmospheric pressure sensor and calculatesboost pressure.

INSTRUCTOR NOTE: For more information on the variable speedfan, refer to the Service Manual "Variable Speed Fan Clutch" (FormSENR8603).

1. Fan control solenoidvalve

• Fan speed sensor(not shown)

• Fan speed overrides

3. Turbo outlet pressuresensor

2. Jacket water coolanttemperature sensor

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• Engine oil renewalsystem components:

1. Oil filter

2. Oil renewal solenoid

3. Fuel pressureregulator

• Oil mixes with fuel infuel tank

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1

3

2

Engine Oil Renewal System: Located on the right side of the engine arethe components of the optional engine oil renewal system. Engine oilflows from the engine block through an oil filter (1) to the engine oilrenewal solenoid (2). A small amount of oil flows from the engine oilrenewal solenoid into the return side of the fuel pressure regulator (3).The engine oil returns to the fuel tank with the return fuel.

The engine oil mixes with the fuel in the tank and flows with the fuel tothe EUI injectors to be burned.

When the engine oil renewal system is used, the operator must pay closeattention to the ADD OIL message that the VIMS provides to the operatorwhen makeup oil must be added.

The oil does not have to be changed when using the engine oil renewalsystem. When the engine oil renewal system is used, the engine oilfilters, the engine oil renewal system filter, the primary fuel filter and thesecondary fuel filters must all be changed at 500 hour intervals.

Engine oil samples must be taken regularly to ensure that the soot level ofthe engine oil is in a safe operating range.

• Sample engine oil tocheck soot level

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• Oil injectioncontrolled by EngineECM

• Engine oil renewalsystem parameters

STMG 70611/98

The ECM regulates the amount of oil that is injected by the engine oilrenewal solenoid. Several parameters must be met before the ECM willallow the injection of oil through the engine oil renewal system. Theparameters that must be met are:

- Fuel position is greater than 10.

- Engine rpm is between 1100 and 1850 rpm.

- Jacket water temperature is between 63°C (145°F) and107°C (225°F).

- Oil filter differential pressure at high idle with warm oil is less than70 kPa (10 psi).

- Fuel filter differential pressure is less than 140 kPa (20 psi).

- Fuel level is greater than 10%.

- Engine oil level switches are sending a valid signal to the EngineECM.

- Engine has been running more than five minutes.

The engine oil renewal system can be turned ON or OFF with the ECAPor ET service tool. The amount of oil injected can also be adjusted byprogramming the ECM with the ECAP or ET service tool. The factorysetting shown in the service tool is "0" and is equivalent to a 0.5% oil tofuel ratio. The ratio can be changed with the service tool from minus 50(-50) to plus 50 (+50), which is equivalent to 0.25% to 0.75% oil to fuelratios.

INSTRUCTOR NOTE: The optional Engine Oil Renewal Systemwas not available at first shipment of the 785C and 789C trucks.

• Oil renewal adjustedwith ECAP or ET

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2

The engine oil level switches (1 and 2) provide input signals to the EngineECM. The Engine ECM provides a signal to the VIMS, which informsthe operator of the engine oil level.

If the truck is equipped with the engine oil renewal system attachment,the upper oil level switch (1) will tell the operator when makeup oil mustbe added. The ADD ENG OIL message is a Category 1 Warning.

The lower oil level switch (2) will tell the operator when the engine oillevel is low and it is unsafe to operate the truck without causing damageto the engine. The ENG OIL LEVEL LOW message is a Category 2 or 3Warning.

If the Engine ECM detects a low oil level condition (oil level below thelower switch), the ECM will log a low oil level event. No factorypassword is required to clear this event.

1. Add engine oil levelswitch

2. Engine oil level lowswitch

• Low oil level event

- 88 -

• 789C cooling systemcapacity increased

1. 789C cooling systemshunt tank

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Cooling System

Shown is a 789C truck. The capacity of the 789C cooling system hasbeen increased by 40% from 474 Liters (125 gal.) to 663 Liters (175 gal.).The radiator is larger and a shunt tank (1) has been added above theradiator. The shunt tank provides a positive pressure at the coolant pumpinlets to prevent cavitation during high flow conditions.

The cooling system is divided into two systems. The two systems are thejacket water cooling system and the aftercooler cooling system. The onlyconnection between these two systems is a small hole in the separatorplate in the shunt tank. The small hole in the shunt tank prevents areduction of coolant from either of the two systems if leakage occurs inone of the separator plates in the radiator top or bottom tank. Whenservicing the cooling systems, be sure to drain and fill both systemsseparately.

The coolant levels are checked at the shunt tank. Use the gauges (2) ontop of the shunt tank to check the coolant level.

A coolant level switch (3) is located on each side of the shunt tank tomonitor the coolant level of both cooling systems (guard removed forviewing switch). The coolant level switches provide input signals to theVIMS, which informs the operator of the engine coolant levels.

Pressure relief valves (4) prevent the cooling systems from becoming overpressurized.

4. Pressure relief valves

3. Coolant levelswitches


• Engine coolingsystems:- Jacket water cooling

system

- Aftercooler coolingsystem

- 89 -

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Shown is the 785C radiator. The 785C is not equipped with a shunt tank.The coolant levels are checked at the radiator top tank. Use the gauges(1) on the top tank to check the coolant level.

Two coolant level switches (2) are located on the top tank to monitor thecoolant level of both cooling systems. The coolant level switches provideinput signals to the VIMS, which informs the operator of the enginecoolant levels.

Pressure relief valves (3) prevent the cooling systems from becoming overpressurized.

The jacket water cooling system uses the cores on the right side of theradiator (approximately 60% of the total capacity). The jacket watercooling system temperature is controlled by temperature regulators(thermostats).

The aftercooler cooling system uses the cores on the left side of theradiator (approximately 40% of the total capacity). The aftercoolercooling system does not have thermostats in the circuit. The coolantflows through the radiator at all times to keep the turbocharged inlet aircool for increased horsepower.

• Aftercooler coolingsystem

• Jacket water coolingsystem

3. Pressure relief valves

2. Coolant levelswitches


- 90 -

1. Jacket water pump

2. Bypass tube

3. Jacket waterthermostat housing

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The jacket water pump (1) is located on the right side of the engine. Thepump draws coolant from the bypass tube (2) until the temperatureregulators (thermostats) open. The thermostats are located in the housing (3) at the top of the bypass tube. When the thermostats are open,coolant flows through the radiator to the water pump inlet.

If the jacket water cooling system temperature increases above 107°C(226°F), the Engine ECM will log an event that requires a factorypassword to clear.

• High coolanttemperature event

- 91 -

• Coolant flow warningswitch (arrow)

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Coolant flows from the jacket water pump, past the coolant flow warningswitch (arrow), and through the various system oil coolers (engine, hoistconverter and brake, and the transmission).

The coolant flow switch sends an input signal to the Engine ECM. TheEngine ECM provides the input signal to the VIMS, which informs theoperator of the coolant flow status.

If the ECM detects a low coolant flow condition, a low coolant flow eventwill be logged. A factory password is required to clear this event.

• Low coolant flowevent

- 92 -

1. Engine oil cooler

2. Hoist, converter andbrake oil coolers

3. Tube to transmissionoil cooler

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Shown is the right side of the engine. The engine oil cooler (1) and thehoist, converter and brake oil coolers (2) are visible in this view. Jacketwater coolant flows through these coolers and through the tube (3) to thetransmission oil cooler.

Jacket water coolant flows through the transmission oil cooler, the engineoil cooler and the hoist, converter and brake oil coolers to both sides ofthe engine cylinder block. Coolant flows through the engine block andthrough the cylinder heads. From the cylinder heads, the coolant flows tothe temperature regulators and either goes directly to the water pumpthrough the bypass tube or to the radiator (depending on the temperatureof the coolant).

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• Jacket water coolingcircuit

TRANSMISSION OIL COOLER

ENGINE OIL COOLER

HOIST, CONVERTER ANDBRAKE OIL COOLER

ENGINEBLOCK

JACKET WATER COOLANT FLOW THERMOSTATHOUSING

RADIATOR

JACKETWATER PUMP

SHUNTTANK

HOIST, CONVERTER ANDBRAKE OIL COOLER

Shown is the jacket water cooling circuit. Coolant flows from the jacketwater pump through the coolers to the engine block. Coolant flowsthrough the engine block and the cylinder heads. From the cylinderheads, the coolant flows to the temperature regulators (thermostats) andeither goes directly to the water pump through the bypass tube or to theradiator (depending on the temperature of the coolant).

The shunt tank (789C only) increases the cooling capacity and provides apositive pressure at the coolant pump inlet to prevent cavitation duringhigh flow conditions.

In this illustration and those that follow, the colors used to identify thevarious pressures in the systems are:

Red - Supply oil/water pressureGreen - Drain or tank oil/waterRed and White Stripes - Reduced supply oil pressureBrown - Lubrication or cooling pressureOrange - Pilot or load sensing signal pressureBlue - Blocked oilYellow - Moving componentsPurple - Air pressure

- 94 -

1. Aftercooler waterpump

2. 789C shunt tanksupply tube

3. Aftercooler circuitcoolant tube

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The auxiliary (aftercooler) water pump (1) for the aftercooler coolingsystem is located on the left side of the engine. Coolant enters theaftercooler water pump from the radiator or the shunt tank supply tube (2)on the 789C truck. Coolant flows from the pump to the aftercooler coresthrough the large tube (3)

- 95 -

1. Rear aftercoolertemperature sensor

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Located in a tube at the rear of the aftercooler is the rear aftercoolertemperature sensor (1). The rear aftercooler temperature sensor providesan input signal to the Engine ECM. The Engine ECM uses the rearaftercooler temperature sensor signal with the jacket water temperaturesensor signal, the brake temperature sensor signals (four) and the airconditioner compressor pressure signal to control the variable speed fanattachment.

The Engine ECM also provides the input signal to the VIMS, whichinforms the operator of the aftercooler coolant temperature. If the rearaftercooler temperature increases above 107°C (226°F), the Engine ECMwill log an event that requires a factory password to clear.

Coolant flows through the aftercooler cores to the front brake oil cooler (2) located at the rear of the engine.

Coolant flows through the front brake oil cooler to the aftercooler sectionof the radiator. The aftercooler cooling system does not have temperatureregulators (thermostats) in the circuit.

When the service or retarder brakes are ENGAGED, the front brake oilcooler diverter valve (3) allows brake cooling oil to flow through the frontbrake oil cooler.

Normally, front brake cooling oil is diverted around the cooler and goesdirectly to the front brakes. Diverting oil around the cooler provideslower temperature aftercooler air during high power demands (whenclimbing a grade with the brakes RELEASED, for example).

• Rear aftercoolertemperature event

• Aftercooler coolingcircuit does not havethermostats

3. Front brake oil coolerdiverter valve

2. Front brake oil cooler

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• Aftercooler coolingcircuit

AFTERCOOLER COOLANT FLOW

FRONT BRAKEOIL COOLER

RADIATOR

AFTERCOOLERWATER PUMP

SHUNTTANK

AFTERCOOLER

Shown is the aftercooler cooling circuit. Coolant flows from theaftercooler water pump through the aftercooler.

Coolant flows through the aftercooler core to the front brake oil coolerlocated at the rear of the engine.

Coolant then flows through the front brake oil cooler to the aftercoolersection of the radiator. The aftercooler cooling circuit does not havetemperature regulators (thermostats) in the circuit.

On the 789C truck, the shunt tank increases the cooling capacity andprovides a positive pressure at the aftercooler water pump inlet to preventcavitation during high flow conditions.

The 785C truck does not have a shunt tank.

• 789C shunt tank

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• Engine oil pump

1. Engine oil pumprelief valve

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Lubrication System

Shown is the 3512B engine used in the 785C truck. The engine oil pumpis located behind the jacket water pump on the right side of the engine.The pump draws oil from the oil pan through a screen. The relief valve (1) for the lubrication system is located on the pump.

The engine also has a scavenge pump at the rear of the engine to transferoil from the rear of the oil pan to the main sump.

Oil flows from the pump through an engine oil cooler bypass valve (2) tothe engine oil cooler (3). The bypass valve for the engine oil coolerpermits oil flow to the system during cold starts when the oil is thick or ifthe cooler is plugged.

On the 3512B engine used in the 785C truck, engine oil samples can betaken at the Scheduled Oil Sampling (S•O•S) tap (4).

2. Engine oil coolerbypass valve

3. Engine oil cooler


- 98 -

• Engine oil filters

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Oil flows from the engine oil cooler to the oil filters on the left side of theengine. The oil flows through the filters and enters the engine cylinderblock to clean, cool and lubricate the internal components and theturbochargers.

Engine oil is added at the fill tube (1) and checked with the dipstick (2).A bypass valve for each filter is located in each oil filter base. Engine oilsamples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3) (789C only). (See Slide No. 80 for the 785C S•O•S tap location.)

The engine has two oil pressure sensors. One sensor is located on eachend of the oil filter base. The front sensor measures engine oil pressurebefore the filters. The rear sensor (4) measures oil pressure after thefilters. The sensors send input signals to the Engine ECM. The ECMprovides the input signal to the VIMS, which informs the operator of theengine oil pressure. Used together, the two engine oil pressure sensorsinform the operator if the engine oil filters are restricted.

If the engine oil pressure is less than 44 kPa (6.4 psi) at LOW IDLE toless than 250 kPa (36 psi) at HIGH IDLE, the Engine ECM will log anevent that requires a factory password to clear.

If the oil filter restriction exceeds 70 kPa (10 psi), a low oil filterrestriction event will be logged. No factory password is required to clearthis event. If the oil filter restriction exceeds 200 kPa (29 psi), a high oilfilter restriction event will be logged. A factory password is required toclear this event.

4. Engine oil pressuresensors

• Engine oil filterrestriction events

• Engine oil pressureevent

1. Engine oil fill tube

2. Engine oil dipstick


- 99 -


• Trapped engine oildrain (arrow)

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Shown is the 3512B engine used in the 785C truck. The 3512B engineuses three oil filters located on the left side of the engine. The 3512Bengine also has a fitting (arrow) that can be used to drain the engine oiltrapped above the filters. Do not add oil through the fitting (arrow)because unfiltered oil will enter the engine. Any contamination couldcause damage to the engine.

NOTICE

When changing the engine oil filters, drain the engine oil trappedabove the oil filters through the fitting (arrow) to prevent spilling theoil. Oil added to the engine through the fitting will go directly to themain oil galleries without going through the engine oil filters. Addingoil to the engine through the fitting may introduce contaminants intothe system and cause damage to the engine.

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• Engine oil system

ENGINEBLOCK

ENGINE OIL SYSTEM

ENGINEOIL COOLER

ENGINEOIL FILTERS

ENGINEOIL PUMP

SCAVENGEPUMP

BYPASSVALVE

ENGINEOIL RENEWAL

SYSTEM SOLENOID

TO FUELSYSTEM

The engine oil pump draws oil from the oil pan through a screen.

The engine also has a scavenge pump at the rear of the engine to transferoil from the rear of the oil pan to the main sump.

Oil flows from the pump through an engine oil cooler bypass valve to theengine oil cooler. The bypass valve for the engine oil cooler permits oilflow to the system during cold starts when the oil is thick or if the cooleris plugged.

Oil flows from the engine oil cooler to the oil filters. The oil flowsthrough the filters and enters the engine cylinder block to clean, cool andlubricate the internal components and the turbochargers.

Some trucks are equipped with an engine oil renewal system. Engine oilflows from the engine block through an oil filter to an engine oil renewalsystem manifold. A small amount of oil flows from the engine oilrenewal system manifold into the return side of the fuel pressure regulator.The engine oil returns to the fuel tank with the return fuel (see Slides No. 69 and 70).

• Engine oil renewalsystem

- 101 -

• Primary fuel filter(arrow)

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Fuel System

The fuel tank is located on the left side of the truck. Fuel is pulled fromthe tank through the fuel heater (not shown), if equipped, and through theprimary fuel filter (arrow) by the fuel transfer pump located on the rightside of the engine behind the engine oil pump.

- 102 -

1. Fuel transfer pump

2. Fuel transfer pumpbypass valve

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The fuel transfer pump (1) is located behind the engine oil pump. Thefuel transfer pump contains a bypass valve (2) to protect the fuel systemcomponents from excessive pressure. The bypass valve setting is higherthan the setting of the fuel pressure regulator (see Slide No. 87). Fuelflows from the transfer pump through the Engine ECM to the secondaryfuel filters located on the left side of the engine.

- 103 -

• Secondary fuel filters

1. Fuel priming pump

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The secondary fuel filters and the fuel priming pump (1) are locatedabove the engine oil filters on the left side of the engine. The fuelpriming pump is used to fill the filters after they are changed.

Fuel filter restriction is monitored with a fuel filter bypass switch (2)located on the fuel filter base. The fuel filter bypass switch provides aninput signal to the Engine ECM. The ECM provides a signal to theVIMS, which informs the operator if the secondary fuel filters arerestricted.

If fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restrictionevent is logged. No factory password is required to clear this event.

Fuel flows from the fuel filter base through the Electronic Unit Injection(EUI) fuel injectors (see Slide No. 60), the fuel pressure regulator andthen returns to the fuel tank. The injectors receive 4 1/2 times the amountof fuel needed for injection. The extra fuel is used for cooling.

NOTE: If the fuel system requires priming, it may be necessary toblock the fuel return line during priming to force the fuel into theinjectors.

2. Fuel filter bypassswitch

• Fuel flows to EUIinjectors

• Extra fuel coolsinjectors

• Fuel filter restrictionevent

- 104 -

1. Fuel pressure tubesto injectors

2. Fuel pressureregulator

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Fuel flows from the fuel filter base through the steel tubes (1) to the EUIfuel injectors. Return fuel from the injectors flows through the fuelpressure regulator (2) before returning to the fuel tank. Fuel pressure iscontrolled by the fuel pressure regulator.

Fuel pressure should be 482 + 138 - 103 kPa (70 + 20 - 15 psi) at FullLoad rpm.

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• Fuel system circuit

FUELTANK

PRIMARYFUEL

FILTER

SECONDARYFUEL FILTERS

ENGINEBLOCK

ENGINE OILRENEWAL

SYSTEM SOLENOID

FUELPRESSURE

REGULATOR

FUELTRANSFER

PUMP

FUELHEATER

ENGINE ECM

CYLINDERHEAD

FUEL SYSTEM

Fuel is pulled from the tank through a fuel heater, if equipped, and sentthrough the primary fuel filter by the fuel transfer pump. Fuel flows fromthe transfer pump through the Engine ECM to the secondary fuel filters.

Fuel flows from the fuel filter base through the fuel injectors in thecylinder heads. Return fuel from the injectors flows through the fuelpressure regulator before returning through the fuel heater to the tank.

If equipped with the engine oil renewal system, engine oil flows from theengine block through an oil filter to the engine oil renewal systemmanifold. A small amount of oil flows from the engine oil renewalsystem manifold into the return side of the fuel pressure regulator. Theengine oil returns to the fuel tank with the return fuel.

The engine oil mixes with the fuel in the tank and flows with the fuel tothe injectors to be burned.

- 106 -

• 789C truck

1. Air filter restrictionindicators

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Air Induction and Exhaust System

The engine receives clean air through the air filters located on the front ofthe truck (789C) or on either side of the engine (785C). Any restrictioncaused by plugged filters can be checked at the filter restriction indicators(1). If the yellow piston is in the red zone, the filters must be cleaned orreplaced.

Check the dust valves (2) for plugging. If necessary, disconnect theclamp and open the cover for additional cleaning. The dust valve isOPEN when the engine is OFF and closes when the engine is running.The dust valve must be flexible and close when the engine is running orthe precleaner will not function properly and the air filters will have ashortened life. Replace the rubber dust valve if it becomes hard and notflexible.

The VIMS will also provide the operator with an air filter restrictionwarning when the filter restriction is approximately 6.2 kPa (25 in. of water). Black exhaust smoke is also an indication of air filterrestriction.

Two filter elements are installed in the filter housings. The large elementis the primary element and the small element is the secondary element.

2. Dust valves

• Large primary element

• Small secondaryelement

- 107 -

1. Turbocharger inletpressure sensor

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The turbocharger inlet pressure sensor (1) is located in a tube between theair filters and the turbochargers. The Engine ECM uses the turbochargerinlet pressure sensor in combination with the atmospheric pressure sensorto determine air filter restriction. The ECM provides the input signal tothe VIMS, which informs the operator of the air filter restriction.

If air filter restriction exceeds 6.25 kPa (25 in. of water), an air filterrestriction event will be logged, and the ECM will derate the fuel delivery(maximum derating of 20%) to prevent excessive exhaust temperatures.A factory password is required to clear this event. If the Engine ECMdetects a turbocharger inlet pressure sensor fault, the ECM will derate theengine to the maximum rate of 20%. If the Engine ECM detects aturbocharger inlet and atmospheric pressure sensor fault at the same time,the ECM will derate the engine to the maximum rate of 40%.

The Engine ECM will automatically inject ether from the ether cylinders (2) during cranking. The duration of automatic ether injectiondepends on the jacket water coolant temperature. The duration will varyfrom 10 to 130 seconds. The operator can also inject ether manually withthe ether switch in the cab on the center console (see Slide No. 48). Themanual ether injection duration is 5 seconds. Ether will be injected onlyif the engine coolant temperature is below 10°C (50°F) and engine speedis below 1900 rpm.

2. Ether cylinders

• Air filter restrictionevent

- 108 -

• 3516B has fourturbochargers(arrows)

• 3512B has twoturbochargers

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Shown is the 3516B engine used in the 789C truck. The 3516B engine isequipped with four turbochargers (arrows). The 785C truck has a 3512Bengine with two turbochargers.

The turbochargers are driven by the exhaust gas from the cylinders whichenters the turbine side of the turbochargers. The exhaust gas flowsthrough the turbochargers, the exhaust piping, and the mufflers.

The clean air from the filters enters the compressor side of theturbochargers. The compressed air from the turbochargers flows to theaftercoolers. After the air is cooled by the aftercoolers, the air flows tothe cylinders and combines with the fuel for combustion.

- 109 -

• Exhaust temperaturesensor (arrow)

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An exhaust temperature sensor (arrow) is located in each exhaustmanifold before the turbochargers. The two exhaust temperature sensorsprovide input signals to the Engine ECM. The ECM provides the inputsignal to the VIMS, which informs the operator of the exhausttemperature.

Some causes of high exhaust temperature may be faulty injectors, pluggedair filters, or a restriction in the turbochargers or the muffler.

If the exhaust temperature is above 750°C (1382°F), the Engine ECM willderate the fuel delivery to prevent excessive exhaust temperatures. TheECM will derate the engine by 2% for each 30 second interval that theexhaust temperature is above 750°C (1382°F) (maximum derate of 20%).The ECM will also log an event that requires a factory password to clear.

• Causes of highexhaust temperature

• High exhausttemperature deratesengine and logs event

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• Air induction andexhaust system

MUFFLER

FROM AIRFILTERS

AFTERCOOLER

3512BAIR INDUCTION

ANDEXHAUST SYSTEM

FROM AIRFILTERS

This schematic shows the flow through the air induction and exhaustsystem.

The turbochargers are driven by the exhaust gas from the cylinders whichenters the turbine side of the turbochargers. The exhaust gas flowsthrough the turbochargers, the exhaust piping, and the mufflers.

The clean air from the filters enters the compressor side of theturbochargers. The compressed air from the turbochargers flows to theaftercoolers. After the air is cooled by the aftercoolers, the air flows tothe cylinders and combines with the fuel for combustion.

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• Power traincomponents:

- Torque converter

- Transfer gears

- Transmission

- Differential

- Final drives

POWER TRAIN

785C

POWER TRAIN

Power flows from the engine to the rear wheels through the power train.The components of the power train are:

- Torque converter

- Transfer gears

- Transmission

- Differential

- Final drives

INSTRUCTOR NOTE: In this section of the presentation, componentlocations and a brief description of the component functions areprovided. For more detailed information on the torque converter andICM (Individual Clutch Modulation) transmission, refer to theTechnical Instruction Module "769C - 793B Off-highway Trucks--Torque Converter and Transmission Hydraulic System" (FormSEGV2591).

- 112 -

• Torque converter:

- Provides a fluidcoupling

- Multiplies torque

- Provides direct driveoperation

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Torque Converter

The first component in the power train is the torque converter. The torqueconverter provides a fluid coupling that permits the engine to continuerunning with the truck stopped. In converter drive, the torque convertermultiplies engine torque to the transmission. At higher ground speeds, alockup clutch engages to provide direct drive. The NEUTRAL andREVERSE ranges are converter drive only. FIRST SPEED is converterdrive at low ground speed and direct drive at high ground speed.SECOND through SIXTH SPEEDS are direct drive only. The torqueconverter goes to converter drive between each shift (during clutchengagement) to provide smooth shifts.

Mounted on the torque converter are the inlet relief valve (1), the outletrelief valve (2) and the torque converter lockup clutch control valve (3).

A torque converter outlet temperature sensor (4) provides an input signalto the Transmission/Chassis ECM. The Transmission/Chassis ECM sendsthe signal to VIMS, which informs the operator of the torque converteroutlet temperature.

A Converter Output Speed (COS) sensor (5) sends an input signal to theTransmission/Chassis ECM. The Transmission/Chassis ECM sends thesignal to the VIMS. The VIMS uses the signal to calculate if any slippageexists in the torque converter lockup clutch or any of the transmissionclutches.

1. Inlet relief valve

2. Outlet relief valve

3. Lockup clutchcontrol valve

4. Outlet temperaturesensor

5. COS sensor

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• CONVERTER DRIVE

- Output shaft rotatesslower than enginerpm

- Torque is increased

• Torque convertercomponents:

- Lockup clutch

- Impeller

- Turbine

- Stator

STATOR

TORQUE CONVERTERCONVERTER DRIVE

LOCKUP PISTON

TORQUE CONVERTERLOCKUP OIL PASSAGE

TURBINE IMPELLER

FREEWHEELASSEMBLY

TORQUE CONVERTERINLET OIL

This sectional view shows a torque converter in CONVERTER DRIVE.The lockup clutch (yellow piston and blue discs) is not engaged. Duringoperation, the rotating housing and impeller (red) can rotate faster than theturbine (blue). The stator (green) remains stationary and multiplies thetorque transfer between the impeller and the turbine. The output shaftrotates slower than the engine crankshaft, but with increased torque.

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• DIRECT DRIVE

- Lockup clutchengaged

- Output shaft rotatesat engine rpm

- Stator freewheels

STATOR

TORQUE CONVERTERDIRECT DRIVE

LOCKUP PISTON

TORQUE CONVERTERLOCKUP OIL PASSAGE

TURBINE IMPELLER

STATOR

FREEWHEELASSEMBLY

TORQUE CONVERTERINLET OIL

In DIRECT DRIVE, the lockup clutch is engaged by hydraulic pressureand locks the turbine to the impeller. The housing, impeller, turbine, andoutput shaft then rotate as a unit at engine rpm. The stator, which ismounted on a freewheel assembly, is driven by the force of the oil in thehousing and will freewheel at approximately the same rpm.

- 115 -

• Torque converterpump has three orfour sections:

1. Torque converterscavenge

2. Torque convertercharging

3. Parking brakerelease

4. Rear brake oilcooling (789C only)

5. Torque converterscavenge screencover

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Torque Converter Hydraulic System

The three (785C) or four (789C) section torque converter pump is locatedat the bottom rear of the torque converter. The four sections (from thefront to the rear) are:

- Torque converter scavenge (1)

- Torque converter charging (2)

- Parking brake release (3)

- Rear brake oil cooling (4) (789C only)

Excess oil that accumulates in the bottom of the torque converter isscavenged by the first section of the pump through a screen behind theaccess cover (5) and returned to the hydraulic tank.

- 116 -

1. Torque convertercharging filter

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Oil flows from the torque converter charging section of the pump to thetorque converter charging filter (1).

An oil filter bypass switch (2) is located on the torque converter chargingfilter. The oil filter bypass switch provides an input signal to the VIMS,which informs the operator if the filter is restricted.

2. Torque convertercharging filter bypassswitch

- 117 -

1. Torque converterinlet relief valve

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Oil flows from the torque converter charging filter to the torque converterinlet relief valve (1). The inlet relief valve limits the maximum pressureof the supply oil to the torque converter. The torque converter inlet reliefpressure can be measured at this valve by removing a plug and installing apressure tap. Inlet relief pressure should not exceed 930 ± 35 kPa (135 ± 5 psi) at high idle when the oil is cold. Normally, the inlet reliefpressure will be slightly higher than the outlet relief valve pressure.

Oil flows through the inlet relief valve and enters the torque converter.

Some of the oil will leak through the torque converter to the bottom of thehousing to be scavenged. Most of the oil in the torque converter is usedto provide a fluid coupling and flows through the torque converter outletrelief valve (2). The outlet relief valve maintains the minimum pressureinside the torque converter. The main function of the outlet relief valve isto keep the torque converter full of oil to prevent cavitation. The outletrelief pressure can be measured at the tap (3) on the outlet relief valve.The outlet relief pressure should be:

785C: 345 to 585 kPa (50 to 85 psi) at 1640 ± 65 rpm (TC Stall)

789C: 345 to 585 kPa (50 to 85 psi) at 1715 ± 65 rpm (TC Stall)

A torque converter outlet temperature sensor (4) provides an input signalto the Transmission/Chassis ECM. The Transmission/Chassis ECM sendsa signal to VIMS, which informs the operator of the torque converteroutlet temperature.

2. Torque converteroutlet relief valve

3. Torque converteroutlet relief pressuretap

4. Torque converteroutlet temperaturesensor

- 118 -

1. Torque converteroutlet screen

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Most of the oil from the torque converter outlet relief valve flows throughthe torque converter outlet screen (1) located outside the left frame.

A torque converter outlet screen bypass switch (2) provides an inputsignal to the VIMS, which informs the operator if the torque converteroutlet screen is restricted.

Oil flows from the torque converter outlet screen to the front brake oilcooler located behind the engine.

Oil flows from the parking brake release section of the torque converterpump to the parking brake release filter (3).

A parking brake release filter bypass switch (4) is located on the parkingbrake release filter. The bypass switch provides an input signal to theBrake ECM. The Brake ECM sends a signal to VIMS, which informs theoperator if the parking brake release filter is restricted.

2. Torque converteroutlet screen bypassswitch

4. Parking brake releasefilter bypass switch

3. Parking brake releasefilter

- 119 -

1. Front brake oil coolerdiverter valve

2. Front brake oil cooler

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The oil from the torque converter outlet screen flows through a divertervalve (1) before flowing through the front brake oil cooler (2). When theretarder or service brakes are ENGAGED, the oil is diverted through thecooler to the brakes. When the brakes are RELEASED, the oil bypassesthe cooler and flows directly to the brakes.

Diverting oil around the cooler provides lower temperature aftercooler airduring high power demands (when climbing a grade with the brakesRELEASED, for example).

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1. Parking brake releasevalve

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Oil from the parking brake release filter flows to the parking brake releasevalve (1). The parking brake release section of the torque converter pumpprovides supply oil for several purposes:

- Release the parking brakes

- Engage the torque converter lockup clutch

- Hoist valve pilot oil

- Front (789C) or rear (785C) brake oil cooling

The parking brake relief valve (2) controls the pressure for parking brakerelease, torque converter lockup and hoist valve pilot oil. The parkingbrake release pressure is 4700 ± 200 kPa (680 ± 30 psi).

Most of the oil from the parking brake release valve flows to the frontbrake oil cooler on the 789C truck and to the rear brake oil coolers on the785C truck.

2. Parking brake relief

• Most oil used forbrake cooling

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1. Torque converterlockup clutch valvesupply port

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1

4

2

The parking brake release pump supplies oil to the torque converterlockup clutch valve through the inlet port (1). When the lockup clutchsolenoid (located on the transmission housing) is energized by theTransmission/Chassis ECM, transmission pump supply oil (signal oil)enters the lockup valve through the center hose (2). The signal oilpressure is approximately 1725 kPa (250 psi). The signal oil causes thelockup valve to start the modulation process for torque converter lockup.The lockup clutch valve then supplies oil to ENGAGE the lockup clutchin the torque converter.

Torque converter lockup clutch pressure can be measured at the tap (3).Torque converter lockup clutch pressure should be 2135 ± 70 kPa (310 ± 10 psi) at 1300 rpm or higher. Do not check the torque converterlockup clutch pressure below 1300 rpm.

The Converter Output Speed (COS) sensor (4) sends an input signal to theTransmission/Chassis ECM. The Transmission/Chassis ECM memoryalso contains the engine rpm and the Transmission Output Speed (TOS)for each gear of the transmission. The Transmission/Chassis ECMprovides all of these input signals to the VIMS.

Using the information from the Transmission/Chassis ECM, the VIMScalculates if any slippage exists in the torque converter lockup clutch orany transmission clutches and stores this information in the VIMS mainmodule. This information can be downloaded from the VIMS with alaptop computer.

3. Torque converterlockup clutchpressure tap

• Do not test converterlockup pressurebelow 1300 rpm

4. Converter outputspeed sensor

• Clutch slippage isrecorded in VIMS

2. Torque converterlockup clutch signaloil supply hose

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• Lockup clutch valveoperation

LOCKUPSOLENOID

FROMTRANSMISSION

CHARGEPUMP

RELAY VALVE

LOCKUPREDUCING

VALVE

LOCKUPMODULATION

VALVE

LOCKUP CLUTCHPILOT PRESSURE

(RV)

TO LOCKUPCLUTCH (LU)

FROMPARKING BRAKE

RELEASE PUMP (PMP)

TORQUE CONVERTER LOCKUP CLUTCH CONTROLDIRECT DRIVE

SHUTTLEVALVE

SELECTORPISTON

TOTRANSMISSION

LUBE

TOSTATION

"D"

SIGNAL OIL

Shown is a sectional view of the torque converter lockup clutch valve inDIRECT DRIVE. Supply oil from the parking brake release pump is usedto provide lockup clutch oil.

First, supply pressure is reduced to provide pilot pressure to the relayvalve. Supply oil to the pressure reduction valve flows through cross-drilled orifices in the spool, past a check valve and enters the slugchamber. The check valve dampens spool movement and reduces thepossibility of valve chatter and pressure fluctuation. Oil pressure movesthe slug in the right end of the spool to the right and the spool moves tothe left against the spring force. The slug reduces the effective area onwhich the oil pressure can push. Because of the reduced effective area, asmaller, more sensitive spring can be used. Pilot pressure will be equal tothe force of the spring on the left end of the spool. The spring force canbe adjusted with shims. Pilot pressure is 1725 ± 70 kPa (250 ± 10 psi).

• Supply pressure isreduced to pilotpressure

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When the lockup solenoid is energized, transmission pump supply(signal) pressure is directed to the relay valve. Before moving theselector piston, the pilot oil moves a shuttle valve to the right, whichcloses the lower left drain passage and opens the check valve. Oil thenflows to the selector piston. Moving the selector piston blocks the upperdrain passage, and the load piston springs are compressed.

When the solenoid is energized, supply oil from the parking brake releasepump is reduced to provide the lockup clutch pressure. Lockup clutchpressure depends mainly on the force of the load piston valve springs.When the solenoid is energized, pilot oil moves the selector piston downagainst a stop. When the load piston that compresses the springs is at thetop against the selector piston, lockup clutch pressure is at its lowestcontrolled value. This value is called "primary pressure." As the loadpiston moves down, lockup clutch pressure increases gradually until theload piston stops. Maximum lockup clutch pressure is then reached. Thegradual increase in pressure, which depends on how fast the load pistonmoves, is called "modulation."

The speed of the load piston movement depends on how fast the oil canflow to the area above the load piston. The load piston orifice meters theflow of oil to the load piston chamber and determines the modulationtime.

Primary pressure is adjusted with shims in the load piston. Final lockupclutch pressure is not adjustable. If the primary pressure is correct andfinal lockup clutch pressure is incorrect, the load piston should bechecked to make sure that it moves freely in the selector piston. If theload piston moves freely, the load piston springs should be replaced.

• Lockup clutch atprimary pressure

• Lockup clutch atmaximum pressure

• Primary pressure isadjusted with shims

• Load piston orificedeterminesmodulation time

• Lockup solenoidenergized startsclutch modulation

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• 789C torque converterhydraulic system

• Scavenge pumpsection

TORQUE CONVERTERHYDRAULIC SYSTEM

FRONTBRAKES

TORQUE CONVERTERCHARGING FILTER


PARKINGBRAKE

RELEASEVALVE

DIVERTERVALVE

CONVERTEROUTLETSCREEN

PARKINGBRAKEFILTER

REAR BRAKEOIL COOLERS

REARBRAKES

TO HOISTSOLENOIDMANIFOLD

CONVERTERSCAVENGE

SCREEN

OUTLETRELIEF VALVE

INLETRELIEF VALVE

CONVERTERLOCKUPVALVE

This schematic shows the flow of oil from the torque converter pumpthrough the torque converter hydraulic system on the 789C truck.

The scavenge pump section pulls oil through a screen from the torqueconverter housing and sends the oil to the hydraulic tank.

The charging pump section sends oil through the torque convertercharging filter to the torque converter inlet relief valve. Oil flows fromthe inlet relief valve through the torque converter to the outlet relief valve.Oil flows from the outlet relief valve through the converter outlet filterand the front brake oil cooler to the front brakes.

The parking brake release pump section sends oil through the parkingbrake release filter to the parking brake release valve and the torqueconverter lockup clutch valve. Most of the oil flows through the parkingbrake release valve and the front brake oil cooler to the front brakes.

The brake cooling pump section of the torque converter pump (789Conly) sends oil through the two oil coolers located on the right side of theengine to the rear brakes.

• Parking brake releasepump section

• Charging pumpsection

• 789C rear brakecooling pump section

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1. Transfer gears

2. Transmission

3. Differential

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Transmission and Transfer Gears

Power flows from the torque converter through a drive shaft to thetransfer gears (1). The transfer gears are splined to the transmission inputshaft.

The transmission (2) is located between the transfer gears and thedifferential (3). The transmission is electronically controlled andhydraulically operated as in all other ICM (Individual Clutch Modulation)transmissions in Caterpillar rigid frame trucks.

The differential is located in the rear axle housing behind thetransmission. Power from the transmission flows through the differentialand is divided equally to the final drives in the rear wheels. The finaldrives are double reduction planetaries.

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1. Transmission lubesupply hose

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3

1

Oil flows from the transmission oil cooler to the transfer gears through ahose (1). Transmission lube oil flows through the transfer gears and thetransmission to cool and lubricate the internal components.

The transmission lube pressure relief valve is in the transmission casenear the transmission hydraulic control valve. The relief valve limits themaximum pressure in the transmission lube circuit. Transmission lube oilpressure can be measured at the tap (2).

At HIGH IDLE, the transmission lube pressure should be 140 to 205 kPa (20 to 30 psi). At LOW IDLE, the transmission lube pressure should be aminimum of 4 kPa (.6 psi).

The Transmission Output Speed (TOS) sensor (3) is located on the frontof the transfer gears. A small shaft runs from the speed sensor locationthrough the entire length of the transmission and engages the transmissionoutput shaft. The transmission speed sensor signal serves many purposes.Some of the purposes are:

- Transmission automatic shifting

- Speedometer operation

- Traction Control System (TCS) top speed limit

- Truck Production Management System (TPMS) distancecalculations

- Machine speed input to VIMS to determine some warning categories

2. Transmission lube oilpressure tap

3. Transmission outputspeed sensor

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• Transmission ispower shift planetarydesign

1 2 3

45 6

POWER SHIFT PLANETARY TRANSMISSION

The transmission is a power shift planetary design which contains sixhydraulically engaged clutches. The transmission provides sixFORWARD speeds and one REVERSE speed.

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• Transmission threesection pump:

1. Transmissionscavenge

2. Transmission lube

3. Transmissioncharging

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2

Transmission Hydraulic System

The transmission pump pulls oil through a suction screen from thetransmission tank (see Slides No. 12 and 159) located on the right side ofthe truck.

The three section transmission pump is mounted on the rear of the pumpdrive, which is located inside the right frame near the torque converter.The three sections are:

- Transmission scavenge (1)

- Transmission lube (2)

- Transmission charging (3)

The transmission scavenge section pulls oil through the magnetic screenslocated at the bottom of the transmission. The scavenged oil from thetransmission is sent to the transmission tank.

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• Transmissionmagnetic scavengescreens (arrow)

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Shown is the location of the transmission magnetic scavenge screens (arrow). These screens should always be checked for debris if aproblem with the transmission is suspected.

Oil is scavenged from the transmission by the first section of thetransmission pump (see Slide No. 110).

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1. Transmissioncharging filter

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23

4

Oil flows from the charging section of the transmission pump to thetransmission charging filter (1) located on the frame behind the right fronttire.

Oil flows from the transmission charging filter to the transmission controlvalve located on top of the transmission. A transmission oil temperaturesensor (2) is located in the tube between the transmission charging filterand the transmission control valve. The temperature sensor provides aninput signal to the Transmission/Chassis ECM. TheTransmission/Chassis ECM sends a signal to VIMS, which informs theoperator of the transmission oil temperature.

Oil flows from the lube section of the transmission pump to thetransmission lube filter (3).

Oil flows from the transmission lube filter through the transmission oilcooler to the transfer gears. Transmission lube oil flows through thetransfer gears and the transmission to cool and lubricate the internalcomponents.

An oil filter bypass switch is located on each filter. The oil filter bypassswitches provide input signals to the Transmission/Chassis ECM. TheTransmission/Chassis ECM sends signals to the VIMS, which informs theoperator if the filters are restricted.

Transmission oil samples can be taken at the Scheduled Oil Sampling(S•O•S) tap (4).

3. Transmission lubefilter

2. Transmission oiltemperature sensor

4. Transmission S•O•Stap

• Oil filter bypassswitches

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1. Transmission oilcooler bypass valve

2. Transmission oilcooler

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2

Oil flows from the transmission lube filter and the transmission controlvalve through the transmission oil cooler bypass valve (1) to thetransmission oil cooler (2). The bypass valve for the transmission oilcooler permits oil flow to the system during cold starts when the oil isthick or if the cooler is restricted.

Oil flows from the transmission oil cooler to the transfer gears and thetransmission to cool and lubricate the internal components.

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4

5

2 1

The transmission charging pump supplies oil to the transmissionhydraulic control valve and the shift solenoids through the inlet port (1).Excess transmission charging oil either drops to the bottom of the housingto be scavenged or flows to the transmission oil cooler through the outlet hose (2).

The torque converter lockup clutch solenoid (3) is energized by theTransmission/Chassis ECM when DIRECT DRIVE (lockup clutchENGAGED) is required. Transmission charge pump supply (signal) oilflows through the small hose (4) to the lockup clutch control valve. Thelockup clutch control valve then engages the lockup clutch.

The transmission charging pressure relief valve is part of the transmissionhydraulic control valve. The relief valve limits the maximum pressure inthe transmission charging circuit. Transmission charging pressure can bemeasured at the tap (5).

1. Transmission controlvalve supply port

2. Transmissioncharging oil returnport

3. Torque converterlockup clutchsolenoid

4. Lockup clutch signaloil hose

5. Transmissioncharging pressuretap

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1. Transmission clutchpressure taps

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2

Shown is the Individual Clutch Modulation (ICM) transmission hydrauliccontrol valve. Transmission clutch pressures are measured at the pressuretaps (1).

The transmission hydraulic control valve contains a priority valve. Thepriority valve controls the pressure that is directed to the selector pistonsin each of the clutch stations. The transmission priority valve pressure is1720 kPa (250 psi).

The transmission lube pressure relief valve (2) limits the maximumpressure in the transmission lube circuit.

The "D" Station (3) is used to control the dual stage relief valve settingfor the clutch supply pressure. In DIRECT DRIVE, the pressuremeasured at the tap for station "D" will be approximately 1380 kPa (200psi). This valve station is adjusted to obtain the correct transmissioncharge pressure in DIRECT DRIVE.

At LOW IDLE in TORQUE CONVERTER DRIVE, transmissioncharging pressure should be 2515 kPa (365 psi) minimum. At HIGHIDLE in TORQUE CONVERTER DRIVE, transmission chargingpressure should be 3175 kPa (460 psi) maximum.

3. "D" Station controlsdual stage relief valve

• Priority valvepressure

2. Transmission luberelief valve

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During torque converter lockup (DIRECT DRIVE), clutch supplypressure is reduced to extend the life of the transmission clutch seals. At1300 rpm in DIRECT DRIVE, the clutch supply pressure should be 2020 + 240 - 100 kPa (293 + 35 - 15 psi). The correspondingtransmission charge pressure is reduced to 2100 ± 100 kPa (305 ± 15 psi).

To test the transmission clutch pressures in torque converter lockup(DIRECT DRIVE), disconnect the signal line (4) and install a plug in thehose and a cap on the fitting. An 8T5200 Signal Generator/Counter canbe used to shift the transmission during the diagnostic tests. If a SignalGenerator is not available, disconnect the upshift and downshift solenoidsand rotate the rotary selector spool manually by inserting a 1/4 in. ratchetextension through the transmission case.

• Test clutch pressuresin DIRECT DRIVE

4. Torque converterlockup signal line

- Disconnect and plugto test in DIRECTDRIVE

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• ICM transmissioncontrols

DOWNSHIFTSOLENOID

UPSHIFTSOLENOID

LOCKUPSOLENOID

F

G

H

A

B

C

ROTARYSELECTOR

SPOOL

NEUTRALIZERVALVEPRIORITY

REDUCTIONVALVE

DOWNSHIFTPRESSURE

UPSHIFTPRESSURE

TRANSMISSION CASE

TRANSMISSIONTANK

CHARGINGPUMP

LUBEPUMP SCAVENGE

PUMP

COOLERBYPASSVALVE

OILCOOLER

LUBRICATIONRELIEF VALVE

PUMPPRESSURE

TO TORQUE CONVERTERRELAY VALVE

SELECTOR VALVE GROUPRELIEF VALVE

TRANSMISSION ICMHYDRAULIC SYSTEM

LOCKUP DUALSTAGE RELIEF VALVE

LUBEPRESSURE

ON

PRESSURE CONTROLGROUP

PILOT OILPRESSURE

D

E

ROTARY ACTUATOR

N1

3

FILTERS

Shown is a sectional view of the ICM transmission hydraulic controlvalve group. The rotary selector spool is in a position that engages twoclutches. Pump supply oil from the lockup solenoid flows to the selectorpiston in station "D." Station "D" reduces the pump supply pressure, andthe reduced pressure flows to the lower end of the relief valve. Providingoil pressure to the lower end of the relief valve reduces the clutch supplypressure.

• Dual stage relief valve

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• Transmissionhydraulic system

• Three section pump:

- Transmissionscavenge

- Transmission lube

- Transmissioncharging

TRANSMISSIONCHARGING

FILTER

SIGNALTO LOCKUP

VALVE RELAY

MAGNETIC SCAVENGESCREENS

TRANSMISSIONLUBE FILTER

TRANSMISSIONOIL COOLER

TRANSMISSIONPUMP

LUBEPORT

785C/789C TRANSMISSION HYDRAULIC SYSTEM

Shown is the transmission hydraulic system. The transmission pump pullsoil through a suction screen from the transmission tank.

The three section transmission pump is mounted on the rear of the pumpdrive, which is located inside the right frame near the torque converter.The three sections are:

- Transmission scavenge

- Transmission lube

- Transmission charging

The transmission scavenge section pulls oil through the magnetic screenslocated at the bottom of the transmission. The scavenged oil from thetransmission is sent to the transmission tank.

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Oil flows from the charging section of the transmission pump to thetransmission charging filter. Oil flows from the transmission chargingfilter to the transmission control valve located on top of the transmission.Transmission charging oil flows from the transmission control valve andjoins with the oil from the transmission lube section of the transmissionpump.

Oil flows from the lube section of the transmission pump to thetransmission lube filter.

Oil from the transmission lube filter and the transmission control valveflows through the transmission oil cooler. Oil flows from thetransmission oil cooler to the transfer gears and the transmission to cooland lubricate the internal components.

• Transmissioncharging section

• Transmission lubesection

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2

3

4

Differential

Shown is the differential removed from the rear axle housing. The rearaxle cooling and filter system starts with a rear axle pump (1) that isdriven by the differential. Since the pump rotates only when the machineis moving, no oil flow is produced when the machine is stationary.Cooling oil flow increases with ground speed to provide cooling when itis most needed.

The rear axle pump pulls oil from the bottom of the rear axle housingthrough a suction screen (2). Oil flows from the pump through atemperature and flow control valve located on top of the differentialhousing to a filter mounted on the rear of the axle housing. Oil then flowsfrom the filter back to the valve located on top of the differential housing.Oil then flows from the valve to the rear wheel bearings and thedifferential bearings.

Oil flows through tubes (3) to the differential bearings.

The fiberglass shroud (4) reduces the temperature of the rear axle oil onlong hauls by reducing the oil being splashed by the bevel gear.

2. Rear axle suctionscreen

3. Differential bearingoil tubes

4. Fiberglass shroud

1. Rear axle pump

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1. Pump supply hose toflow control valve

2. Rear axletemperature and flowcontrol valve

3. Differential oiltemperature sensor

4. Differential oilpressure sensor

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2

1

5

4

Oil flows from the pump through the large hose (1) to the rear axletemperature and flow control valve (2). A differential oil temperaturesensor (3) and pressure sensor (4) are located on the temperature and flowcontrol valve. The sensors provide input signals to the Brake ECM. TheBrake ECM sends signals to the VIMS.

The differential temperature sensor input signal is used to warn theoperator of a high rear axle oil temperature condition or to turn on theattachment rear axle cooling fan (if equipped).

The differential oil pressure sensor input signal is used to warn theoperator of a HIGH or LOW rear axle oil pressure condition.

A LOW oil pressure warning is provided if the pressure is below35 kPa (5 psi) when the differential oil temperature is above 52°C (125°F) and the ground speed is higher than 24 km/h (15 mph).

A HIGH oil pressure warning is provided if the pressure is above 690 kPa(100 psi) when the differential oil temperature is above 52°C (125°F).

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The temperature and pressure control valve (2) prevents high oil pressurewhen the rear axle oil is cold. When the oil temperature is below 43°C(110°F), the valve is OPEN and allows oil to flow to the rear axlehousing. When the oil temperature is above 43°C (110°F), the valve isCLOSED and all the oil flows through the filter to a flow control valvelocated in the temperature and flow control valve. The temperature andpressure control valve is also the system main relief valve. If the pressureexceeds 690 kPa (100 psi), the temperature and pressure control valvewill open to prevent high oil pressure to the rear axle oil filter.

The flow control valve distributes the oil flow to the rear wheel bearingsand the differential bearings.

Oil flows from the temperature and flow control valve to the differentialoil filter mounted on the rear of the axle housing. Oil then flows from thefilter back to the temperature and flow control valve. Some of the oil thatflows from the temperature and flow control valve flows through thesmall supply hose (5) to the differential bearings.

5. Differential bearingoil supply hose

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1. Differential oil filterbypass switch

2. Rear axle oil levelswitches

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3 2

The differential oil filter bypass switch (1) and the two rear axle oil levelswitches (2) (one behind differential filter) provide input signals to theBrake ECM. The Brake ECM sends signals to the VIMS.

The differential oil filter bypass switch signal is used to warn the operatorwhen the differential oil filter is restricted.

The rear axle oil level switch input signals are used to warn the operatorwhen the rear axle oil level is LOW.

When the truck is initially put into operation, a 1R0719 (40 micron) filteris installed. This filter removes the rust inhibitor used duringmanufacturing. The 40 micron filter should be changed after the first

50 hours of operation and replaced with a 4T3131 (13 micron) filter. The13 micron filter should be changed every 500 hours.

A differential carrier thrust pin is located behind the small cover (3). Thethrust pin prevents movement of the differential carrier during high thrustload conditions.

3. Differential carrierthrust pin cover

• Differential oil filterservice information

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• Rear axle oil coolingand filter system

OIL COOLER OILFILTER

TEMPERATURE/PRESSURE

CONTROL VALVE

REAR AXLEOIL COOLING AND FILTER SYSTEM

FLOW CONTROL VALVE

DIFFERENTIALOIL PUMP

SUCTIONSCREEN

REAR AXLE

Shown is a schematic of the rear axle oil cooling and filter system. Thedifferential oil pump pulls oil from the bottom of the rear axle housingthrough a suction screen. Oil flows from the pump through a temperatureand flow control valve located on top of the differential housing.

The temperature and pressure control valve, which is part of thetemperature and flow control valve, prevents high oil pressure when therear axle oil is cold. When the oil temperature is below 43°C (110°F), thevalve is OPEN and allows oil to flow to the rear axle housing. When theoil temperature is above 43°C (110°F), the valve is CLOSED and all theoil flows through the differential oil filter and the oil cooler (if equipped)to a flow control valve, which is also part of the temperature and flowcontrol valve.

• Temperature andpressure control valve

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• Temperature andpressure control valveis main relief

STMG 70611/98

The temperature and pressure control valve is also the system main reliefvalve. If the pressure exceeds 690 kPa (100 psi), the temperature andpressure control valve will open to prevent high oil pressure to the rearaxle oil filter.

The flow control valve distributes the oil flow to the rear wheel bearingsand the differential bearings. At high ground speeds, excess oil flow isdiverted to the axle housing to prevent overfilling the wheel bearing andfinal drive compartments.

• Flow control valveprevents overfillingcompartments

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• Double reductionplanetary gear finaldrives

FIRST REDUCTIONRING GEAR

SECOND REDUCTIONRING GEAR

SECOND REDUCTIONCARRIER

SECOND REDUCTIONSUN GEAR

SECOND REDUCTIONPLANETARY GEAR

FIRST REDUCTIONPLANETARY GEAR

FIRST REDUCTIONSUN GEAR

FIRST REDUCTIONCARRIER

FINAL DRIVE

Final Drives

Shown is a sectional view of the double reduction planetary gear finaldrive. Power flows from the differential through axles to the sun gear ofthe first reduction planetary set. The ring gears of the first reductionplanetary set and the second reduction planetary set cannot rotate. Sincethe ring gears cannot rotate, the first reduction sun gear causes rotation ofthe first reduction planetary gears and the first reduction carrier.

The first reduction carrier is splined to the second reduction sun gear. Thesecond reduction sun gear causes rotation of the second reductionplanetary gears and the second reduction carrier. Since the secondreduction carrier is connected to the wheel assembly, the wheel assemblyalso rotates.

The wheel assembly rotates much slower than the axle shaft but withincreased torque.

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Transmission/Chassis Electronic Control System

The Transmission/Chassis Electronic Control Module (ECM) (arrow) islocated in the compartment at the rear of the cab. The transmissioncontrol used in the "B" Series trucks is referred to as the secondgeneration Electronic Programmable Transmission Control (EPTC II).

The transmission control used in the "C" Series trucks performs thetransmission control functions, plus some other machine functions (hoistcontrol). Because of the added functionality of the control, it is nowreferred to as the "Transmission/Chassis ECM."

The Transmission/Chassis ECM does not have a diagnostic window as inthe EPTC II. Diagnostic and programming functions must be performedwith an Electronic Control Analyzer Programmer (ECAP) or a laptopcomputer with the Electronic Technician (ET) software installed. ET isthe tool of choice because the Transmission/Chassis ECM can bereprogrammed with a "flash" file using the WinFlash application of ET.The ECAP cannot upload "flash" files.

The Transmission/Chassis ECM appears identical to the Engine ECMwith two 40-pin connectors, but the Transmission/Chassis ECM does nothave fittings for cooling fluid. Also, the Transmission/Chassis ECM hasno access plate for a personality module.

• Transmission/ChassisECM (arrow)

• Transmission/ChassisECM

- No diagnosticwindow

- Diagnostics andprogrammingrequire ECAP or ET

• Transmission/ChassisECM looks like EngineECM

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• ECM shiftstransmission

HOIST LOWER SOLENOID

BACK-UP ALARMRELAYSTARTER

SOLENOID

SHIFT LEVERPOSITION SWITCH

KEY START SWITCH

UPSHIFT SOLENOID

LOCKUP SOLENOID

BODYPOSITION SENSOR

INPUT COMPONENTS OUTPUT COMPONENTS

TRANSMISSION GEARSWITCH

TRANSMISSION OUTPUTSPEED SENSOR

PARKING/SECONDARY BRAKEPRESSURE SWITCH

SERVICE/RETARDERBRAKE

PRESSURE SWITCH

CONVERTER OUTPUTSPEED SENSOR

ENGINE OUTPUTSPEED SENSOR

HOIST LEVERPOSITION SENSOR

BRAKE ECM

ENGINE ECM

ELECTRONIC SERVICE TOOL

CAT DATA LINK

VIMS

DOWNSHIFT SOLENOID

HOIST RAISE SOLENOID

AUTO LUBE SOLENOID

LOW STEERINGPRESSURE SWITCH

TRANSMISSION CHARGEFILTER SWITCH

TRANSMISSION OILTEMP SENSOR

HOIST SCREEN SWITCH

TRANSMISSION LUBEFILTER SWITCH

TORQUE CONVERTEROIL TEMP SENSOR

BODY UP LAMP

"C" SERIES TRUCKTRANSMISSION/CHASSIS ELECTRONIC CONTROL SYSTEM

The purpose of the Transmission/Chassis ECM is to determine the desiredtransmission gear and energize solenoids to shift the transmission up ordown as required based on information from both the operator andmachine.

The Transmission/Chassis ECM receives information (electrical signals)from various input components such as the shift lever switch,Transmission Output Speed (TOS) sensor, transmission gear switch, bodyposition sensor and the hoist lever sensor.

Based on the input information, the Transmission/Chassis ECMdetermines whether the transmission should upshift, downshift, engagethe lockup clutch or limit the transmission gear. These actions areaccomplished by sending signals to various output components.

Output components include the upshift, downshift and lockup solenoids,the back-up alarm and others.

• Shifts controlled byelectrical signals

• Output components

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The Transmission/Chassis ECM also provides the service technician withenhanced diagnostic capabilities through the use of onboard memory,which stores diagnostic codes for retrieval at the time of service.

The Engine Electronic Control, the Brake Electronic Control System(ARC and TCS), the Vital Information Management System (VIMS) andthe Transmission/Chassis Electronic Control System all communicatethrough the CAT Data Link. Communication between the electroniccontrols allows the sensors of each system to be shared. Many additionalbenefits are provided, such as Controlled Throttle Shifting (CTS). CTSoccurs when the Transmission/Chassis ECM signals the Engine ECM toreduce or increase engine fuel during a shift to lower stress to the powertrain.

The Transmission/Chassis ECM is also used to control the hoist, theautomatic lubrication (grease), the neutral-start and the back-up alarmsystems on the "C" Series trucks.

Many of the sensors and switches that provided input signals to the VIMSinterface modules on the "B" Series trucks have been moved to provideinput signals to the Transmission/Chassis ECM and the Brake ECM.Sensors and switches that were in the VIMS and now provide inputsignals to the Transmission/Chassis ECM are:

- Low steering pressure - Hoist screen bypass

- Transmission oil temperature - Transmission charge filter bypass

- Transmission lube filter bypass - Torque converter oil temperature

The Electronic Control Analyzer Programmer (ECAP) and the ElectronicTechnician (ET) Service Tools can be used to perform several diagnosticand programming functions.

Some of the diagnostic and programming functions that the service toolscan perform are:

- Display real time status of input and output parameters

- Display the internal clock hour reading

- Display the number of occurrences and the hour reading of the firstand last occurrence for each logged diagnostic code and event

- Display the definition for each logged diagnostic code and event

- Display load counters

- Display the lockup clutch engagement counter

- Display the transmission gear shift counter

- Program the top gear limit and the body up gear limit

- Upload new Flash files

• Benefits of electroniccommunication

• Transmission/ChassisECM controls hoistand other systems

• Diagnostic andprogrammingfunctions

• Sensors signalTransmission/ChassisECM

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1. Shift lever switch

- Switch-type input

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2

3

The shift lever (also referred to as the "Cane" or "Gear Selector") switch (1) is located inside the cab in the shift console and provides inputsignals to the Transmission/Chassis ECM. The shift lever switch controlsthe desired top gear selected by the operator. The shift lever switch inputsconsist of six wires. Five of the six wires provide codes to theTransmission/Chassis ECM. Each code is unique for each position of theshift lever switch. Each shift lever switch position results in two of thefive wires sending a ground signal to the Transmission/Chassis ECM.The other three wires remain open (ungrounded). The pair of groundedwires is unique for each shift lever position. The sixth wire is the"Ground Verify" wire, which is normally grounded. The Ground Verifywire is used to verify that the shift lever switch is connected to theTransmission/Chassis ECM. The Ground Verify wire allows theTransmission/Chassis ECM to distinguish between loss of the shift leverswitch signals and a condition in which the shift lever switch is betweendetent positions.

To view the shift lever switch positions or diagnose problems with theswitch, use the VIMS message center module or the status screen of theET service tool and observe the "Gear Lever" status. As the shift lever ismoved through the detent positions, the Gear Lever status should displaythe corresponding lever position shown on the shift console.

The position of the shift lever can be changed to obtain better alignmentwith the gear position numbers on the shift console by loosening the threenuts (2) and rotating the lever. The position of the shift lever switch isalso adjustable with the two screws (3).

2. Shift leveradjustment nuts

3. Shift lever switchadjustment screws

• Shift lever switchdiagnostics

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1. Transmission gearswitch

- Switch type input

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4

3

2

1

The transmission gear switch (1) provides input signals to theTransmission/Chassis ECM. The transmission gear switch inputs (alsoreferred to as the "actual gear inputs") consist of six wires. Five of the sixwires provide codes to the Transmission/Chassis ECM. Each code isunique for each position of the transmission gear switch. Eachtransmission gear switch position results in two of the five wires sendinga ground signal to the Transmission/Chassis ECM. The other three wiresremain open (ungrounded). The pair of grounded wires is unique for eachgear position. The sixth wire is the "Ground Verify" wire, which isnormally grounded. The Ground Verify wire is used to verify that thetransmission gear switch is connected to the Transmission/Chassis ECM.The Ground Verify wire allows the Transmission/Chassis ECM todistinguish between loss of the transmission gear switch signals and acondition in which the transmission gear switch is between gear detentpositions.

Earlier transmission gear switches use a wiper contact assembly that doesnot require a power supply to Pin 4 of the switch. Current transmissiongear switches are Hall-Effect type switches. A power supply is requiredto power the switch. A small magnet passes over the Hall cells, whichthen provide a non-contact position switching capability. The Hall-Effecttype switch uses the same 24-Volt power supply used to power the Transmission/Chassis ECM.

The solenoid outputs provide +Battery voltage to the upshift solenoid (2),the downshift solenoid (3) or the lockup solenoid (4) based on the inputinformation from the operator and the machine. The solenoids areenergized until the transmission actual gear switch signals theTransmission/Chassis ECM that a new gear position has been reached.

2. Upshift solenoid

3. Downshift solenoid

4. Lockup solenoid

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The Transmission Output Speed (TOS) sensor (arrow) is located on thetransfer gear housing on the input side of the transmission. Although thesensor is physically located near the input side of the transmission, thesensor is measuring the speed of the transmission output shaft. Thesensor is a Hall-Effect type sensor. Therefore, a power supply is requiredto power the sensor. The sensor receives 10 Volts from theTransmission/Chassis ECM. The sensor output is a square wave signal ofapproximately 10 Volts amplitude. The frequency in Hz of the squarewave is exactly equal to twice the output shaft rpm. The signal from thissensor is used for automatic shifting of the transmission. The signal isalso used to drive the speedometer and as an input to other electroniccontrols.

The Transmission/Chassis ECM uses the TOS sensor to determine whento shift, but the shifts always occur at a precise engine rpm. The enginerpm is known because the Transmission/Chassis ECM knows the gearratios of the transfer gear, each gear range of the transmission, thedifferential and the final drives. The Transmission/Chassis ECM alsoestimates the circumference of the tires. The Transmission/Chassis ECMuses the gear ratios and tire circumference to calculate the engine rpm forany ground speed.

An 8T5200 Signal Generator/Counter can be used to shift thetransmission during diagnostic tests. Disconnect the harness from thelockup solenoid and the speed sensor and attach the Signal Generator tothe speed sensor harness. Depress the ON and HI frequency buttons.Start the engine and move the shift lever to the highest gear position.Rotate the frequency dial to increase the ground speed and thetransmission will shift.

• TOS sensor (arrow)

• Engine rpm iscalculated for shiftpoints

• 8T5200 SignalGenerator/Counter

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1

5

4

3

2

The service/retarder brake switch (1) is located in the compartmentbehind the cab. The switch is normally closed and opens whenservice/retarder brake air pressure is applied. The switch has twofunctions for the Transmission/Chassis ECM:

- Signals the Transmission/Chassis ECM to use elevated shift points,which provide increased engine speed during downhill retarding forincreased oil flow to the brake cooling circuit.

- Signals the Transmission/Chassis ECM to allow rapid shiftingduring braking by overriding the anti-hunt timer.

A diagnostic code is stored if the Transmission/Chassis ECM does notreceive a closed (ground) signal from the switch within seven hours ofoperation time or an open signal from the switch within two hours ofoperation time.

The Traction Control System (TCS) also uses the service/retarder brakeswitch as an input through the CAT Data Link (see Slide No. 199).

1. Service/retarderbrake switch

• Service/retarderbrakes engaged:

- Raises shift points

- Eliminates anti-hunttimer

• Service/retarderswitch used as TCSinput

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The parking/secondary brake switch (2) is in the parking/secondary brakeair pressure line. The normally open switch is closed during theapplication of air pressure. The purpose of the switch is to signal theTransmission/Chassis ECM when the parking/secondary brakes areENGAGED. Since the parking/secondary brakes are spring engaged andpressure released, the parking/secondary brake switch is closed when thebrakes are RELEASED and opens when the brakes are ENGAGED. Thissignal is used to override the anti-hunt timer for rapid downshifting and isused to sense when the machine is parked.

A diagnostic code is stored if the Transmission/Chassis ECM does notreceive a closed (ground) signal from the switch within seven hours ofoperation time or an open signal from the switch within one hour ofoperation time.

Many relays (3) are located behind the cab. Some of these relays receiveoutput signals from the Transmission/Chassis ECM, and the relays turn onthe desired function. The back-up alarm relay is one of theTransmission/Chassis ECM output components located behind the cab.When the operator moves the shift lever to REVERSE, theTransmission/Chassis ECM provides a signal to the back-up alarm relay,which turns ON the back-up alarm.

Another input to the Transmission/Chassis ECM is the hoist lever sensor(see Slide No. 157). The main function of the hoist lever sensor is to raiseand lower the body, but it is also used to NEUTRALIZE the transmission.If the transmission is in REVERSE when the body is being raised, thehoist lever sensor is used to shift the transmission to NEUTRAL. Thetransmission will remain in NEUTRAL until:

- The hoist lever is moved into the HOLD or FLOAT position.

- The shift lever has been cycled into and out of NEUTRAL.

The system air pressure sensor (4) and the brake light switch (5) are alsolocated in the compartment behind the cab. The low air pressure sensorprovides an input signal to the Brake ECM. The Brake ECM sends asignal to the VIMS, which informs the operator of the system air pressurecondition.

2. Parking/secondarybrake switch

3. Relays

4. System air pressuresensor

5. Brake light switch

• Parking/secondarybrakes engaged:

- Eliminates anti-hunttimer

- Signals parkedmachine

• Hoist lever sensor

- Reverse inhibitoroperation

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1

The body position sensor (1) is located on the frame near the left bodypivot pin. A rod assembly (2) is connected between the sensor and thebody. When the body is raised, the rod rotates the sensor, which changesthe Pulse Width Modulated (PWM) signal that is sent to theTransmission/Chassis ECM. The adjustment of the rod between thesensor and the body is very important. The length of the rod must bewithin 10 mm (.39 in.) of the following dimensions (center to center ofthe rod ends):

785C: 350 ± 3 mm (13.78 ± .12 in.)789C: 50 ± 3 mm (13.78 ± .12 in.)

After the rod has been adjusted, a calibration should be performed. Thebody position sensor is calibrated by the Transmission/Chassis ECMwhen the following conditions occur:

- Engine is running

- Hoist lever is in FLOAT

- No ground speed is present for one minute

- Body position is 6 degrees different than previous calibration

- Duty cycle output from the sensor is less than 20%

Use the VIMS display to view the body position. When the body isdown, the VIMS should display zero degrees. If the position is greaterthan zero degrees, the sensor rod may have to be adjusted.

1. Body position sensor

2. Body position rodassembly

• Body position sensorrod adjustment

• Body position sensorcalibration

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The body position signal is used for several purposes.

- Body up gear limiting

- Hoist snubbing

- Starts a TPMS cycle

- Signals a new load count (after 10 seconds in RAISE position)

- Lights the body up dash lamp

- Allows the VIMS to provide body up warnings

The body position sensor signal is used to limit the top gear into whichthe transmission will shift when the body is UP. The body up gear limitvalue is programmable from FIRST to THIRD gear using the ECAP orET service tool. The Transmission/Chassis ECM comes from the factorywith this value set to FIRST gear. When driving away from a dump site,the transmission will not shift past the programmed gear until the body isdown. If the transmission is already above the limit gear when the bodygoes up, no limiting action will take place.

The body position sensor signal is also used to control the SNUB positionof the hoist control valve. When the body is being lowered, theTransmission/Chassis ECM signals the hoist LOWER solenoid to movethe hoist valve spool to the SNUB position. In the SNUB position, thebody float speed is reduced to prevent the body from making hard contactwith the frame.

The body position sensor signal is used to provide warnings to theoperator when the truck is moving with the body UP. The faster theground speed, the more serious the warning.

INSTRUCTOR NOTE: In the previous slides, only some of the inputand output components of the transmission and chassis control wereshown. Other components will be shown when the system theycontrol is discussed (hoist solenoids for example).

• Hoist SNUB control

• Body up gear limit

• Body up warnings

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STEERING

789C

STEERING SYSTEM

This section of the presentation explains the operation of the steeringsystem. As on other Caterpillar Off-highway Trucks, the steering systemuses hydraulic force to change the direction of the front wheels. Thesystem has no mechanical connection between the steering wheel and thesteering cylinders.

If the oil flow is interrupted while the truck is moving, the systemincorporates a secondary steering system. Secondary steering isaccomplished by accumulators which supply oil flow to maintain steering.

The steering system on the "C" Series trucks is the same as the steeringsystem on the "B" Series trucks. No changes were made to the steeringsystem.

• Steering hydraulicallyoperated

• "C" Series steeringsystem same as "B"Series

• Secondary steeringuses accumulators

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SOLENOID ANDRELIEF VALVE

RETURNMANIFOLD

STEERINGDIRECTIONAL

VALVE

HANDMETERING UNIT

LOW STEERINGPRESSURE SWITCH

HIGH STEERINGPRESSURE SWITCH

RL

P

T

LS

PISTON PUMP

ACCUMULATORCHARGING

VALVE

789C STEERING SYSTEMNO STEER/MAXIMUM FLOW

CASEDRAINFILTER

When the engine is started, oil for the steering system is drawn from thesteering hydraulic tank by the steering pump and sent through a one-waycheck valve to the solenoid and relief valve manifold. Oil from thesolenoid and relief valve manifold flows to the steering directional valve,the accumulator charging valve and the accumulators. After the oilpressure increases to a predetermined pressure in both accumulators, thesteering pump will destroke.

When a steering demand occurs, the accumulators supply the necessaryoil flow for steering, and pressure in the accumulators decreases. Whenthe oil pressure in the accumulators decreases to a predetermined level,the steering pump will automatically upstroke to maintain the oil pressurerequired for steering in the accumulators.

• 789C steering system

• Accumulators supplyoil for normal andsecondary steering

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Oil from the accumulators flows through the steering directional valve tothe Hand Metering Unit (HMU).

If the steering wheel is not turned, the oil flows through the HMU and themain steering oil filter to the tank.

Allowing oil to circulate through the HMU while the steering wheel isstationary provides a "thermal bleed" condition, which maintains atemperature differential of less than 28°C (50°F) between the HMU andthe tank. This "thermal bleed" prevents thermal seizure of the HMU(sticking steering wheel).

When the steering wheel is turned, the HMU directs oil back to thesteering directional valve. The steering directional valve directs oil to thesteering cylinders. Depending on which direction the steering wheel isturned, oil will flow to the head end of one steering cylinder and to therod end of the other cylinder. The action of the oil on the pistons and rodsin the steering cylinders causes the wheels to change direction. Displacedoil from the steering cylinders flows through the back pressure valve inthe steering directional valve and returns through the main steering oilfilter to the tank.

• Orifice in HMUprovides "thermalbleed" to preventseizure

• Steering directionalvalve directs oil tosteering cylinders

• Accumulators directoil to steeringdirectional valve

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CROSSOVERRELIEFVALVES

HANDMETERING

UNIT

PISTONPUMP

PUMPSWITCH

SOLENOID ANDRELIEF VALVE

RETURN MANIFOLD

CASE DRAINFILTER

785C STEERING SYSTEMHOLD

Oil from the steering pump flows through a one-way check valve to thesolenoid and relief valve return manifold and is then sent to theaccumulators and the Hand Metering Unit (HMU). The 785C truck doesnot use a steering directional valve. Oil from the HMU flows through acrossover relief valve group directly to the steering cylinders.

In the HOLD position, oil flows through an orifice in the HMU to thetank. Allowing oil to flow through the HMU in the HOLD positionprovides a "thermal bleed" condition, which prevents thermal seizure ofthe HMU (sticking steering wheel).

The crossover relief valves protect the steering cylinders and oil linesfrom pressure surges when the steering wheel is in the HOLD position byequalizing the oil pressure between the head ends and rod ends of thesteering cylinders.

During a turn, the HMU directs oil through the crossover relief valves tothe steering cylinders. Displaced oil from the steering cylinders flowsback through the HMU to the main steering oil filter.

• 785C steering system

• Orifice in HMUprovides "thermalbleed" to preventseizure

• Crossover reliefvalves protectcylinders and lines

• HMU directs oil tocrossover reliefvalves and steercylinders

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6

3

1

2

4

5

The steering tank is located on the right platform. Two sight gauges areon the side of the tank. When the engine is shut off and the oil is cold, theoil should be visible between the FULL and ADD OIL markings of theupper sight gauge (l). When the engine is running and the accumulatorsare fully charged, the oil level should not be below the ENGINERUNNING marking of the lower sight gauge (2). If the ENGINERUNNING level is not correct, check the nitrogen charge in eachaccumulator. A low nitrogen charge will allow excess oil to be stored inthe accumulators and will reduce the secondary steering capacity.

A combination vacuum breaker/pressure relief valve is used to limit thetank pressure. Before removing the fill cap, be sure that the engine wasshut off with the key start switch and the oil has returned to the tank fromthe accumulators. Depress the pressure release button (3) on the breatherto vent any remaining pressure from the tank.

Supply oil for the steering system is provided by a piston-type pump.Case drain oil from the pump returns to the tank through the filter (4).The remaining steering system oil returns to the tank through the mainsteering filter (5). Both filters are equipped with bypass valves to protectthe system if the filters are restricted or during cold oil start-up.

4. Case drain filter

5. Main steering filter

3. Pressure releasebutton

• Steering tank

1. Upper sight gauge

2. Lower sight gauge

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If the steering pump fails or if the engine cannot be started, the connector (6) is used to attach an Auxiliary Power Unit (APU). The APUwill provide supply oil from the steering tank at the connector to chargethe steering accumulators. Steering capability is then available to tow thetruck.

INSTRUCTOR NOTE: For more information on using the APU,refer to the Special Instructions "Using 1U5000 Auxiliary Power Unit(APU)" (Form SEHS8715) and "Using the 1U5525 AttachmentGroup" (Form SEHS8880).

6. APU secondarysteering connector

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12

The piston-type steering pump (1) for the 785C truck is mounted to thepump drive. The pump drive is located on the inside of the right framerail near the torque converter.

The steering pump operates only when the engine is running and providesthe necessary oil flow to the accumulators for steering system operation.

The steering pump for the 785C truck contains a pressure compensatorvalve (2) that monitors and controls steering pump output.

2. Pressurecompensator valve

1. 785C steering pump

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• 785C steering pump

- Maximum flow

• Swashplate atmaximum angleallows maximum flow

SWASHPLATE PISTON

SUPPLY OIL

OUTPUTOIL

PRESSURE COMPENSATORVALVE

CONTROL PISTONSPRING

785C STEERING PUMPMAXIMUM FLOW

Shown is a sectional view of the piston-type steering pump for the 785Ctruck in the MAXIMUM FLOW condition. No oil pressure is present inthe control piston. In this condition, the swashplate is kept at maximumangle by the force of the spring in the pump housing. The pistons travelin and out of the barrel and maximum flow is provided through the outletport. Since the pump is driven by a shaft off the engine, it should beremembered that engine rpm also affects pump output.

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• 785C pumpcompensator valve

- Maximum flow

TOCONTROL PISTON

DRAIN PASSAGES

PUMP COMPENSATOR VALVE

MAXIMUM PUMP FLOW

TOCONTROL PISTON

DRAIN PASSAGES

MINIMUM PUMP FLOW

FROMPUMP

FROMPUMP

Shown is a sectional view of the pump compensator valve for the 785Ctruck. The pump compensator valve senses pump supply pressure througha passage in the valve body. When the outlet pressure is less than theforce of the spring on the end of the compensator spool, the oil is blockedfrom flowing to the pump control piston.

As the accumulators fill, the pressure of the oil through the pump outletincreases. The pump supply pressure will increase until the pressure ofthe oil in the pump passage in the pump compensator valve is high enoughto overcome the spring force on the compensator spool. The spool thenmoves to the left and opens the passage to the control piston. Thismovement occurs when the outlet oil pressure is approximately 17580 ± 345 kPa (2550 ± 50 psi).

The pressure setting can be adjusted by changing the shim thicknessbehind the compensator spool spring. Remove the plug and add shims toincrease the pressure setting. Remove shims to lower the setting.

- Minimumflow/maximumpressure

• Adjust compensatorwith shims

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• 785C steering pump

- Minimumflow/maximumpressure

SWASHPLATE PISTON

SUPPLY OIL

OUTPUT OIL

PRESSURECOMPENSATOR VALVECONTROL PISTON

785C STEERING PUMPMINIIMUM FLOW

The pressure of the oil from the compensator valve passage moves thecontrol piston, which rotates the swashplate toward the minimum angle.The pistons now have very little movement in and out of the barrel as theretraction plate and slippers follow the minimum angle of the swashplate.

While the accumulators are filled, this small movement of the pistonsmaintains the pressure at the setting of the pressure compensator valve.The compensator spool will remain open to provide pressure oil behindthe control piston. Excess oil from the pump outlet goes into the pumpcase for cooling and lubrication. The oil then goes through a drain line tothe case drain oil filter and steering hydraulic tank.

As the steering wheel is turned and oil is taken from the accumulators, thepressure at the pump outlet will decrease. When accumulator pressuredecreases, the pressure compensator valve will allow the swashplate tomove toward maximum angle and increase pump output.

• Pump returns tomaximum flow

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43

1

2

The 789C is equipped with a load sensing, pressure compensated, piston-type pump (1). The steering pump is mounted to the pump drive.The pump drive is located on the inside of the right frame rail near thetorque converter.

The steering pump operates only when the engine is running and providesthe necessary flow of oil to the accumulators for steering systemoperation. The steering pump contains a load sensing controller (2) thatworks with an accumulator charging valve to monitor and control steeringpump output.

The steering pump will produce flow at high pressure until the steeringaccumulators are charged with oil and the pressure increases to 18300 ± 350 kPa (2655 ± 50 psi) at LOW IDLE. This pressure is referredto as the CUT-OUT pressure. When the CUT-OUT pressure is reached,the accumulator charging valve reduces the load sensing signal pressureto the pump load sensing controller, and the pump destrokes to the LOWPRESSURE STANDBY condition. During LOW PRESSURESTANDBY, the pressure should be between 2070 and 3600 kPa (300 and 525 psi).

The pump operates at minimum swashplate angle to supply oil forlubrication and leakage. Because of the normal leakage in the steeringsystem and Hand Metering Unit (HMU) "thermal bleed", the pressure inthe accumulators will gradually decrease to 16470 ± 350 kPa (2390 ± 50 psi). This pressure is referred to as the CUT-IN pressure.

1. Steering pump

• CUT-OUT pressure

• LOW PRESSURESTANDBY

2. Load sensingcontroller

• CUT-IN pressure

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When the pressure in the accumulators decreases to the CUT-IN pressure,the accumulator charging valve blocks the load sensing signal line to theload sensing controller from returning to the tank, and the pump upstrokesto maximum displacement (full flow).

A pressure tap (3) is located on the pump pressure switch manifold. Ifsteering pump supply pressure is measured at this tap during LOWPRESSURE STANDBY, a gauge acceptable for testing maximumsteering system pressure must be used to avoid damaging the gauge whenthe steering pump upstrokes to provide maximum oil flow.

Two pressure switches monitor the condition of the steering system on the789C. One switch (4) monitors the output of the steering pump. Thisswitch monitors pump supply pressure during LOW PRESSURESTANDBY. The VIMS refers to this switch as the "low steeringpressure" switch.

The other steering pressure switch is mounted on the bottom of one of thesteering accumulators (see Slide No. 153). This switch monitors thesteering system accumulator pressure. The VIMS refers to this switch asthe "high steering pressure" switch.

Both steering pressure switches provide input signals to theTransmission/Chassis ECM. The Transmission/Chassis ECM sendssignals to the VIMS, which informs the operator of the condition of thesteering system. A steering system warning is only displayed if theground speed is above 8 km/h (5 mph) or the actual gear switch is not inNEUTRAL.

4. Low steeringpressure switch

• High steeringpressure switch

• Steering pressurewarning only above 8 km/h (5 mph)

3. LOW PRESSURESTANDBY pressuretap

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4

6

2

1

3

5

On the 789C truck, steering pump supply oil flows through a check valve (1) to the solenoid and relief valve manifold (2). The solenoid andrelief valve manifold connects the steering pump to the accumulatorcharging valve (3), the accumulators and the steering directional valve (4). The solenoid and relief valve manifold also provides a path todrain for the steering oil.

When checking the steering system CUT-OUT and CUT-IN pressures, agauge can be connected at the pressure tap (5).

Steering system oil samples can be taken at the steering system ScheduledOil Sampling (S•O•S) tap (6).

• 789C trucks

1. Check valve

2. Solenoid and reliefvalve manifold

3. Accumulatorcharging valve

4. Steering directionalvalve

5. Steering systempressure tap

6. Steering systemS•O•S tap

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• Steering pumpoperation

• Actuator pistondrained duringmaximum flow

PUMP OUTPUT

LOAD SENSINGPRESSURE

ACCUMULATORCHARGING

VALVE

TO ACCUMULATORS

FROM ACCUMULATORS

LOAD SENSINGCONTROLLER

FLOWCOMPENSATOR

SWASHPLATEPISTON

ACTUATORPISTON

MAXIMUM FLOW789C STEERING PUMP

After the engine is started, pressure increases in the steering accumulators.The pump load sensing controller is spring biased to vent the actuatorpiston pressure to drain. Venting pressure from the load sensing controllerand the actuator piston positions the spring biased swashplate tomaximum displacement (full flow).

As pressure increases in the accumulators, pump supply pressure is sensedin the accumulator charging valve and on both ends of the flowcompensator. With pressure on both ends of the flow compensator, theswashplate is kept at maximum angle by the force of the spring in thepump housing and pump discharge pressure on the swashplate piston.The pistons travel in and out of the barrel and maximum flow is providedthrough the outlet port. Since the pump is driven by the engine, enginerpm also affects pump output.

NOTE: Because the signal lines are sensing pump supply pressureand not a "load" pressure, the steering system does not operate thesame as other load sensing systems with a margin pressure.

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• Accumulator chargingvalve shifts

• Signal pressuredecreases

PUMP OUTPUT

LOAD SENSINGPRESSURE

LOW PRESSURE STANDBY

TO ACCUMULATORS

FROM ACCUMULATORS

LOAD SENSINGCONTROLLER

789C STEERING PUMP

FLOWCOMPENSATOR

ACCUMULATORCHARGING

VALVE

SWASHPLATEPISTON

ACTUATORPISTON

Pump supply pressure will increase until the accumulator pressure actingon the accumulator charging valve shifts the spool, and the load sensingsignal pressure is vented to the tank. The accumulator charging valvespool shifts (cut-out) when the pump outlet oil pressure is approximately18300 ± 350 kPa (2655 ± 50 psi).

An orifice prevents supply pressure from filling the drained load sensingpassage above the flow compensator. Pump oil (at low pressure standbypressure) flows past the lower end of the displaced flow compensatorspool to the actuator piston. The actuator piston has a larger surface areathan the swashplate piston. The oil pressure at the actuator pistonovercomes the spring force of the swashplate piston and moves theswashplate to destroke the pump. The pump is then at a low flow, LOWPRESSURE STANDBY condition. Pump output pressure is equal to thesetting of the flow compensator. The LOW PRESSURE STANDBYsetting must be between 2070 and 3600 kPa (300 and 525 psi).

• Pump at LOWPRESSURE STANDBY

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In the NEUTRAL or NO STEER position, demand for oil from theaccumulators is low. The pump operates at minimum swashplate angle tosupply oil for lubrication and leakage. Because of the normal leakage inthe steering system and HMU "thermal bleed.", the pressure in theaccumulators will gradually decrease to approximately 16470 ± 350 kPa(2390 ± 50 psi) (90% of the accumulator charging valve cut-out pressure).

When the pressure in the accumulators decreases to 16470 ± 350 kPa(2390 ± 50 psi), the accumulator charging valve shifts (cut-in) and blocksthe load sensing signal line pressure from the tank. Pump supply oilflows through the orifice and pressurizes the load sensing signal line. Theload sensing signal shifts the flow compensator spool and drains theactuator piston oil to the tank. Venting pressure from the actuator pistonpositions the spring biased swashplate to maximum displacement (fullflow).

At LOW lDLE in the NEUTRAL or NO STEER position, the pump willcycle between the cut-out and cut-in conditions in 25 seconds or more.Connecting a pressure gauge to the pressure tap on the bottom of thesteering directional valve will indicate these steering system pressures. Ifpump pressure cycles in less than 25 seconds, leakage is in the system andmust be corrected. Typical sources of leakage can be the accumulatorbleed down solenoid or the back-up relief valve located on the returnmanifold.

• Charging valve shiftswhen accumulatorpressure decreases

• Pump returns to fullflow

• Steering pump cycletime

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21

3

Shown is the accumulator charging valve (1). The accumulator chargingvalve is located on the frame rail near the front of the truck and below theengine oil pan.

The pressure setting of the accumulator charging valve can be changed byadjusting the spring force that keeps the valve seated (closed). Changethe setting by removing the protective cap (2) and turning the adjustmentscrew clockwise to increase or counterclockwise to decrease the pressuresetting. Do not exceed 14 N•m (10 lb. ft.) torque on the adjustment screwwhen making the adjustments. One turn of the adjustment screw changesthe pressure approximately 4000 kPa (580 psi).

Operate the engine at LOW IDLE and check the pump (accumulator)pressure at the pressure tap (3). The pump will cycle between cut-out andcut-in every 25 seconds or more. The pressure gauge will indicate thesesteering system pressures. Turn the adjusting screw until the cut-outpressure is correct.

If the accumulator charging pressure cannot be adjusted withinspecifications, an adjustment of the high pressure cutoff valve is required.The high pressure cutoff setting must be a minimum of 1720 kPa (250 psi) higher than the accumulator charging valve setting.

NOTE: When testing or adjusting any steering system pressuresettings, always allow the accumulator charge cycle to occur at leastthree times before testing the pressures. Failure to allow the chargingcycle to occur three times will result in inaccurate readings.

1. Accumulatorcharging valve

• Adjusting chargingvalve

2. Protective cap

• Allow three chargingcycles before testingpressures

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• Adjusting highpressure cutoff

LOAD SENSING CONTROLLER

HIGH PRESSURE CUTOFFADJUSTMENT SCREW

TO TANK

TO ACTUATOR PISTON

FROM PUMP OUTPUT PORT

LOW PRESSURESTANDBY ADJUSTMENT

SCREW

ACCUMULATORCHARGING VALVE

FROMACCUMULATOR

DISCONNECT ANDPLUG LINE FOR

HIGH PRESSURECUTOFF TEST

TOACCUMULATOR

Pump pressure limiting (high pressure cutoff) is adjustable. To adjust thepump high pressure cutoff valve, turn the accumulator charging valveadjustment screw all the way in, or disconnect the load sensing (LS) line(pump to accumulator charging valve) at the pump. Plug the line to theaccumulator charging valve and cap the fitting on the pump. Operate theengine at LOW IDLE, and check the pump (accumulator) pressure at thepressure tap below the steering directional valve.

Turn the compensator (high pressure cutoff) adjusting screw whilewatching the pressure gauge. One turn is equal to approximately 2800 kPa (405 psi). Adjust the pressure to 20000 ± 350 kPa (2900 ± 50 psi). When the adjustment is complete, reconnect the LS lineto the pump.

The high pressure cutoff setting must be a minimum of 1720 kPa (250 psi)higher than the accumulator charging valve setting. If the high pressurecutoff setting of the compensator valve (in the load sensing controller) islower than the accumulator charging valve setting, the pump will stay atMINIMUM FLOW, and the steering system will take too long to recharge.The high pressure cutoff adjustment provides a back-up if the accumulatorcharging valve malfunctions.

- Disconnect loadsensing line

- Adjust high pressurecutoff adjustingscrew

• Cutoff setting must behigher than chargingvalve setting

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• Adjusting lowpressure standby

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Pump LOW PRESSURE STANDBY is also adjustable. Connect a gaugeto the low pressure standby pressure tap (see Slide No. 138). With thesignal line connected, operate the engine at LOW IDLE and check thepump pressure. The pump will cycle to low pressure standby every 25 seconds or more. Low pressure standby must be between 2070 and 3600 kPa (300 and 525 psi). If adjustment is required, stop theengine.

Turn the low pressure standby adjustment screw clockwise to increase thepressure and counterclockwise to decrease the pressure until the pressureis between 2070 and 3600 kPa (300 and 525 psi). Each 1/4 turn changesthe pressure setting approximately 345 kPa (50 psi).

NOTE: If the steering pump is adjusted on a hydraulic test stand, setthe margin pressure to 2070 ± 100 kPa (300 ± 15 psi) with a flow of 115 ± 12 L/min (30 ± 3 gpm), 1838 rpm and 15000 kPa (2180 psi)discharge pressure. The low pressure standby reading measured on atruck is higher than the test stand margin pressure due to parasiticloads in the truck steering system.

- 174 -

• 789C solenoid andrelief valve manifold

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1

43

2

5

On the 789C truck, steering pump supply oil flows through a check valve(1) to the solenoid and relief valve manifold. The solenoid and reliefvalve manifold connects the steering pump to the accumulator chargingvalve, the accumulators and the steering directional valve. The solenoidand relief valve manifold also provides a path to drain for the steering oil.

The check valve (1) prevents accumulator oil from flowing back to thesteering pump when the pump destrokes to LOW PRESSURESTANDBY.

The accumulator bleed down solenoid (2) drains pressure oil from theaccumulators when the truck is not in operation.

The back-up relief valve (3) protects the system from pressure spikes ifthe pump cannot destroke fast enough or limits the maximum pressure ifthe steering pump high pressure cutoff valve does not open.

Steering system oil samples can be taken at the steering system ScheduledOil Sampling (S•O•S) tap (4)

To operate the steering system on a disabled truck, an Auxiliary PowerUnit (APU) can be connected to the secondary steering connector (5) onthe solenoid and relief valve manifold and to a suction port on thehydraulic tank (see Slide No. 133). The APU will provide supply oil tocharge the accumulators. Steering capability is then available to tow thetruck.

2. Accumulator bleeddown solenoid

5. Secondary steeringconnector


3. Back-up relief valve

1. Check valve

- 175 -

• 785C solenoid andrelief valve manifold

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2

6

5

4

1

3

On the 785C truck, steering pump supply oil flows through a check valve(1) to the solenoid and relief valve manifold. The solenoid and reliefvalve manifold connects the steering pump to the accumulators and theHMU. The solenoid and relief valve manifold also provides a path todrain for the steering oil.

The check valve (1) prevents accumulator oil from flowing back to thesteering pump

The accumulator bleed down solenoid (not shown) drains pressure oilfrom the accumulators when the truck is not in operation.

The back-up relief valve (2) limits the maximum pressure if the steeringpump compensator valve fails.

Steering system oil samples can be taken at the steering system ScheduledOil Sampling (S•O•S) tap (3)

To operate the steering system on a disabled truck, an Auxiliary PowerUnit (APU) can be connected to the secondary steering connector (4) onthe solenoid and relief valve manifold and to a suction port on thehydraulic tank (see Slide No. 133). The APU will provide supply oil tocharge the accumulators. Steering capability is then available to tow thetruck.

The 785C has two accumulators (5). The steering system pressure tap (6)is located on the bottom of the left steering accumulator.

• Accumulator bleeddown solenoid (notshown)

4. Secondary steeringconnector

5. Steering accumulator



2. Back-up relief valve

1. Check valve

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• Solenoid and reliefvalve manifold

BACKUP RELIEF VALVE

BLEED DOWNSOLENOID

TOTANK

FROM ACCUMULATORS

SOLENOID AND RELIEF VALVE MANIFOLD

Shown is a sectional view of the solenoid and relief valve manifold. Theaccumulator bleed down solenoid is energized by the bleed down solenoidshutdown control (see Slide No. 154) when the key start switch is movedto the OFF position. The bleed down solenoid shutdown control holds thesolenoid open for 70 seconds.

Pressure oil from the accumulators is sensed by the bleed down solenoid.When the solenoid is ENERGIZED, the plunger moves and connects thepressure oil to the drain passage. Pressure oil flows through an orifice,past the plunger, to the tank. The orifice limits the return oil flow fromthe accumulators to a rate which is lower than the flow limit (restriction)of the steering oil filter in the hydraulic tank. When the solenoid is DE-ENERGIZED, spring force moves the plunger and pressure oil cannotgo to drain.

• Bleed down solenoiddrains accumulators

- 177 -

• Back-up relief valveprotects system ifpump does notdestroke

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The back-up relief valve protects the steering system if the steering pumpmalfunctions (fails to destroke). Pressure oil from the steering pumpworks against the end of the back-up relief valve and the spring. Therelief valve unseats (opens) if the pressure reaches approximately:

785C: 22740 ± 350 kPa (3300 ± 50 psi) at 8 ± 2 L/min (2 ± .5 gpm)

789C: 20670 ± 400 kPa (3000 ± 60 psi) at 8 ± 2 L/min (2 ± .5 gpm)

Oil then flows past the relief valve and drains to the tank.

The back-up relief valve must be adjusted only on a test bench. Thepressure setting of the back-up relief valve can be changed by adjustingthe spring force that keeps the relief valve seated (closed). To change therelief valve setting, remove the protective cap and turn the adjustmentscrew clockwise to increase or counterclockwise to decrease the pressuresetting. One revolution of the setscrew will change the pressure setting3800 kPa (550 psi).

A functional test of the back-up relief valve can be performed on themachine by installing a manual hydraulic pump at the location of theAuxiliary Power Unit (APU) connector and installing blocker plates toprevent oil from flowing to the accumulators. See the service manual formore detailed information.

NOTE: Using the functional test procedure to adjust the back-uprelief valve will provide only an approximate setting. Accuratesetting of the back-up relief valve can only be performed on ahydraulic test bench.

• Adjust back-up reliefvalve on test benchonly

• Functional test ofback-up relief valve(on machine)

- 178 -

1. 789C steeringdirectional valve

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2

1

The steering directional valve (1) used on the 789C truck is pilot operatedfrom the HMU in the operator’s station. Five pilot lines connect thesetwo components. The pilot lines send pilot oil from the HMU to shift thespools in the steering directional valve. The spools control the amountand direction of pressure oil sent to the steering cylinders. Four pilot linesare used for pump supply, tank return, left turn and right turn. The fifthpilot line is for the load sensing signal.

When checking the steering system cut-out and cut-in pressures, a gaugecan be connected at the pressure tap (2).


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• Steering directionalvalve components:

- Priority spool

- Amplifier spool withcombiner/checkspool

- Directional spool

- Relief/makeupvalves

- Back pressure valve

RELIEF/MAKEUPVALVE

LEFT TURNCYLINDER BACK PRESSURE

VALVE

LEFT TURNPILOT OIL

AMPLIFIER SPOOL

RIGHT TURNPILOT OIL

COMBINER/CHECKSPOOL

LOADSENSING PORT

FROMACCUMULATOR

PRIORITY SPOOL

STEERINGDIRECTIONAL VALVE

RIGHT TURNCYLINDER

RELIEF/MAKEUPVALVE

HAND METERINGUNIT SUPPLY ANDTHERMAL BLEED

NO TURN

TO TANK

Shown is a sectional view of the steering directional valve. The maincomponents of the steering directional valve are: the priority spool, theamplifier spool with internal combiner/check spool, the directional spool,the relief/makeup valves and the back pressure valve.

Pressure oil from the accumulators flows past the spring biased priorityspool and is blocked by the amplifier spool. The same pressure oil flowsthrough an orifice to the right end of the priority spool. The orificestabilizes the flow to the priority spool and must be present to open andclose the priority spool as the flow demand changes. The same pressureoil flows to the HMU. After all the passages fill with pressure oil, thepriority spool shifts to the left, but remains partially open. In thisposition, the priority spool allows a small amount of oil flow (thermalbleed) to the HMU and decreases the pressure to the HMU supply port.The "thermal bleed" prevents the HMU from sticking.

- 180 -

• Steering directionalvalve in NO STEERposition

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With the truck in the NEUTRAL or NO TURN position, all four workingports (supply, tank, right turn and left turn) are vented to the tank throughthe HMU. The directional spool is held in the center position by thecentering springs.

While the truck is traveling straight (no steer), any rolling resistance(opposition) acting on the steering cylinders creates a pressure increase.The increased pressure acts on the relief/makeup valve in that port. If thepressure increase exceeds 28000 ± 1000 kPa (4065 ± 150 psi), the reliefpoppet will open. A pressure drop occurs across the orifice. The pressuredrop causes the dump valve to move and allows oil to flow to the tankpassage.

The relief action causes the makeup portion of the other relief/makeupvalve to open and replenish oil to the low pressure ends of the cylinders.

The excess (dumped) oil flows across the back pressure valve and entersthe outer end of the other relief/makeup valve. A pressure difference of48 kPa (7 psi) between the tank passage and the low pressure cylinderport causes the makeup valve to open. The excess oil flows into the lowpressure cylinder port to prevent cavitation of the cylinder. The backpressure valve also prevents cavitation of the cylinders by providing apositive pressure of 170 kPa (25 psi) in the passage behind the makeupvalve. A pressure higher than 170 kPa (25 psi) will open the backpressure valve to the tank.

The steering directional valve must be removed and tested on a hydraulictest bench to accurately check the setting of the relief/makeup valves.

A functional test of the relief/makeup valves can be performed on themachine by connecting a manual hydraulic pump and installing blockerplates to prevent oil from flowing to the steering cylinders. See theservice manual for more detailed information.

NOTE: Using the functional test procedure to adjust therelief/makeup valves will provide only an approximate setting.Accurate setting of the relief/makeup valves can only be performedon a hydraulic test bench.

• Relief/makeup valves

• External impact opensa relief valve and amakeup valve

• Back pressure valvesends pressure tomakeup valve

• Adjust relief/makeupvalves on test benchonly

• Functional test ofrelief/makeup valves(on machine)

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• Steering directionalvalve during a RIGHTTURN

AMPLIFIER SPOOL

BACKPRESSURE VALVE

LEFT TURNPILOT OIL

RIGHT TURNPILOT OIL

COMBINER/CHECKSPOOL

LOAD SENSING PORT

FROMACCUMULATOR

HAND METERINGUNIT SUPPLY ANDTHERMAL BLEED

PRIORITY SPOOL

STEERINGDIRECTIONAL VALVE

RIGHT TURN

RELIEF/MAKEUPVALVE

LEFT TURNCYLINDER

RIGHT TURNCYLINDER

RELIEF/MAKEUPVALVE

TO TANK

When the steering wheel is turned to the RIGHT, the "thermal bleed" andventing of the four work ports to the tank is stopped. The increasedsupply pressure flows to the HMU and the load sensing pilot line. Theload sensing pilot line directs cylinder pressure to the priority spool in thedirectional valve. Cylinder pressure is present in the HMU because pilotoil combines with accumulator oil in the combiner/check valve spool inthe directional valve. The increased pressure in the load sensing linecauses the priority spool to move to the right and allows more oil flow tothe HMU through the supply line. The load sensing port supply pressurevaries with the steering load. The priority spool moves proportionally,allowing sufficient oil flow to meet the steering requirements.

Pilot oil flows through a stabilizing orifice to the right turn pilot port ofthe directional valve and moves the directional spool. Movement of thedirectional spool allows pilot oil to flow to the amplifier andcombiner/check spools.

• Pilot oil movesdirectional spool

• Load sensing pilotpressure movespriority spool

- 182 -

• Pilot oil movesamplifier spool

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The pilot oil divides at the amplifier spool. Pilot oil flows through anarrow groove around the combiner/check spool. The pilot oil ismomentarily blocked until the amplifier spool moves far enough to theright to allow partial oil flow through one of eight orifices.

Pilot oil also flows through a connecting pin hole and a stabilizing orificeto the left end of the amplifier spool and causes the amplifier spool tomove to the right. Accumulator oil at the spring end (right end) of theamplifier spool flows through a mid-connecting pin to the left end of theamplifier spool and also causes the amplifier spool to move to the right.

When the amplifier spool moves to the right, accumulator oil flows to theinner chamber, forcing the combiner/check spool to the left. Accumulatoroil then flows through seven of the eight orifices. Pilot and accumulatoroil combine. Oil flows across the directional spool (which has alreadyshifted) for a RIGHT TURN.

The faster the steering wheel is turned, the farther the directional spooland the amplifier spool are shifted. A higher flow rate is available, whichcauses the truck to turn faster. The ratio of pilot and pump supply oil thatcombine is always the same because one orifice is dedicated to pilot flowand seven orifices are dedicated to accumulator supply flow.

Return oil from the cylinders flows across the directional spool, aroundthe relief/makeup valve, forces the back pressure valve open and returnsto the tank.

During a turn, if a front wheel strikes a large obstruction that cannotmove, oil pressure in that steering cylinder and oil line increases. Oilflow to the cylinder is reversed. This pressure spike is felt in theamplifier spool. The combiner/check spool moves to the right and blocksthe seven pump supply oil orifices to the steering cylinders. Theamplifier spool moves to the left and blocks the pilot oil orifice. Pilot oilflow to the steering cylinders stops. The pressure spike is not felt at theHMU. If the pressure spike is large enough, the relief/makeup valvedrains the pressure oil to the tank as previously described.

• Turning steeringwheel faster providesmore flow to cylinders

• Pressure spike movescombiner/check spooland blocks flow toHMU

• Pilot and accumulatoroil combine incombiner/check spool

- 183 -

1. 785C solenoid andrelief valve manifold

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4

2

3

Shown is the solenoid and relief valve manifold (1) and the crossoverrelief valves (2) on the 785C truck.

The crossover relief valves (2) are located in one housing mounted on theinside of the left frame rail near the front of the truck. The crossoverrelief valves prevent damage from high pressure oil in the steeringcylinder circuit caused by an outside force applied to a front wheel whenthe steering wheel is stationary.

The crossover relief valve housing contains two pressure taps (3) wheresteering system pressure can be measured. One tap shows pressure duringa left turn and the other tap shows pressure during a right turn.

To check the steering system pressure, turn the steering wheel completelyin either direction. Operate the engine at LOW IDLE. Continue to turnthe steering wheel after the wheels have stopped and the pressure willincrease to the pump compensator valve setting. Check the steeringpressure while turning in both directions. The pump compensator valvesetting should be observed on the gauge in both directions. If the pressurereadings are different, one of the crossover relief valve settings isprobably incorrect. A misadjusted valve must be removed and readjustedon a test bench.

On the 785C, one pressure switch (4) monitors the condition of thesteering system. The switch provides an input signal to theTransmission/Chassis ECM. The Transmission/Chassis ECM sends asignal to the VIMS.

2. Crossover reliefvalves

- Protect cylindersand lines

• Pressure differencecould indicateincorrect crossoverrelief valve setting

3. Pressure taps

4. Steering systempressure switch

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• Crossover reliefvalves equalizepressure betweensteering cylinders

CROSSOVERRELIEF VALVES

HANDMETERING UNIT

785C CROSSOVER RELIEF SYSTEMEXTERNAL IMPACT

On the 785C truck, when the steering wheel is stationary, the HMU blocksoil in the steering cylinders and in the lines between the steering cylindersand the HMU. The oil blockage prevents the front wheels from movingwhen the steering wheel is not turned. If pressure is applied against thefront wheels while the steering wheel is stationary, the pressure of the oilincreases in the head end of one cylinder and the rod end of the othercylinder. If the increase of oil pressure exceeds 18270 kPa (2650 psi) atthe affected crossover relief valve, the valve will open. Oil from the highpressure ends of the steering cylinders then transfers to the low pressureends of the cylinders.

- 185 -

• 789C HMU (arrow)

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The 789C Hand Metering Unit (HMU) (arrow) is located at the base ofthe steering column behind a cover at the front of the cab. The HMU isconnected to the steering wheel and controlled by the operator.

The 789C HMU meters the amount of oil sent to the steering directionalvalve by the speed at which the steering wheel is turned. The faster theHMU is turned, the higher the flow sent to the steering cylinders from thesteering directional valve, and the faster the wheels will change direction.

The 785C HMU is larger because oil flows directly from the HMU,through the crossover relief valve, to the steering cylinders. The capacityof the 785C HMU must be large enough to handle the flow required to fillthe steering cylinders and allow satisfactory steering cycle times.

On the front of the HMU are four ports:

- Return to tank - Left turn

- Pump supply - Right turn

The 789C HMU has a fifth port on the side of the HMU. The fifth port isthe load sensing signal line to the steering directional valve.

• 789C meters oil todirectional valve

• 785C HMU is larger tohandle more flow

• HMU ports

- 186 -

1. 789C steeringaccumulators

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2

1

Two steering accumulators (1) provide the supply oil during normaloperation and temporary secondary steering if a loss of pump flow occurs(789C shown).

Inside each accumulator is a rubber bladder that is charged with nitrogen.The nitrogen charge provides energy for normal steering and secondarysteering capability if steering pump flow stops.

To check the secondary steering system, the engine must be shut off withthe manual shutdown switch (see Slide No. 25) while leaving the key startswitch in the ON position. When the manual shutdown switch is used,the bleed down solenoid is not energized and the accumulators do notbleed down. The truck can then be steered with the engine stopped.

The steering accumulator pressure switch (2) monitors the steeringaccumulator pressure. The switch provides an input to the VIMS. TheVIMS refers to this switch as the "high steering pressure" switch.

High pressure oil remains in the accumulators if the manualshutdown switch is used. To release the oil pressure in theaccumulators, turn the key start switch to the OFF position and turnthe steering wheel left and right until the oil is drained from theaccumulators (steering wheel can no longer be turned).

WARNING

2. Steering accumulatorpressure switch

• Check secondarysteering

- 187 -

• Shutdown control(arrow)

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Shown is the shutdown control (arrow) for the steering accumulator bleeddown solenoid. The control is located in the compartment behind the cab.

The steering accumulator bleed down solenoid is activated by the controlwhen the key start switch is moved to the OFF position. The bleed downsolenoid shutdown control holds the solenoid open for 70 seconds.

The charge pressure for the steering accumulators is:

785C: 8270 ± 0 kPa (1200 ± 0 psi)

789C: 5512 ± 345 kPa (800 ± 50 psi)• Accumulator charge

pressures

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• Hoist systemcontrolled byTransmission/ChassisECM

HOIST SYSTEM

789C

HOIST SYSTEM

The hoist system on the 785C and 789C trucks is electronically controlledby the Transmission/Chassis ECM. The hoist control system operatessimilarly to the earlier trucks. The four operating positions are: RAISE,HOLD, FLOAT and LOWER.

The hoist valve has a fifth position referred to as the SNUB position. Theoperator is unaware of the SNUB position because a corresponding leverposition is not provided. When the body is being lowered, just before thebody contacts the frame, the Transmission/Chassis ECM signals the hoistsolenoids to move the hoist valve spool to the SNUB position. In theSNUB position, the body float speed is reduced to prevent the body frommaking hard contact with the frame.

• Hoist SNUB control

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The operator controls the hoist lever (arrow). The four positions of thehoist lever are RAISE, HOLD, FLOAT and LOWER.

The truck should normally be operated with the hoist lever in the FLOATposition. Traveling with the hoist in the FLOAT position will make surethe weight of the body is on the frame and body pads and not on the hoistcylinders. The hoist control valve will actually be in the SNUB position.

NOTE: If the truck is started with the body raised and the hoist leverin FLOAT, the lever must be moved into HOLD and then FLOATbefore the body will lower.

• Hoist lever (arrow)

• Hoist lever normally inFLOAT position

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The hoist lever controls a Pulse Width Modulated (PWM) position sensor (arrow). The PWM sensor sends duty cycle input signals to theTransmission/Chassis ECM. Depending on the position of the sensor andthe corresponding duty cycle, one of the two solenoids located on thehoist valve is energized.

The four positions of the hoist lever are RAISE, HOLD, FLOAT andLOWER but since the sensor provides a duty cycle signal that changes forall positions of the hoist lever, the operator can modulate the speed of thehoist cylinders.

The hoist lever sensor also replaces the body raise switch (transmissionneutralizer switch) that was located behind the operator’s seat. The hoistlever sensor performs two functions:

- Raises and lowers the body

- Neutralizes the transmission in REVERSE

• Hoist control positionsensor (arrow)

• Hoist lever sensorperforms twofunctions:

- Raises and lowersbody

- Neutralizestransmission inREVERSE

• Sensor energizes twosolenoids on hoistvalve

• Hoist lever sensorprovides modulation

- 191 -

1. Hoist, converter andbrake tank

2. Oil level sight gauges

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3

1

2

Shown is the hoist, converter and brake oil hydraulic tank (1) and the oillevel sight gauges (2). The oil level is normally checked with the uppersight gauge. The oil level should first be checked with cold oil and theengine stopped. The level should again be checked with warm oil and theengine running.

The lower sight gauge is used when filling the hydraulic tank with thehoist cylinders in the RAISED position. When the hoist cylinders arelowered, the hydraulic oil level will increase. After the hoist cylinders arelowered, check the hydraulic tank oil level with the upper sight gauge asexplained above.

Use only Transmission Drive Train Oil (TDTO) with a specification ofTO-4 or newer.

TDTO-4 oil:

- Provides maximum frictional capability required for clutch discsused in the brakes.

- Increases brake holding capability by reducing brake slippage.

- Controls brake chatter.

Check the hydraulic tank breather (3) for restriction. Clean the filter if itis restricted.

- Lower gauge forfilling tank withcylinders RAISED


3. Breather

- 192 -

• Rear of tanks

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Shown is the rear of the transmission and hoist, converter and brake oilhydraulic tanks. The hoist system pumps pull oil from the hydraulic tankthrough the suction screens (arrows) located in the rear of the tank.• Hoist suction screens

(arrows)

- 193 -

1. Two section hoistpump

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12

2

The hoist system oil for the "C" Series Trucks is supplied by a two sectionpump (1) located at the top rear of the pump drive. Oil flows from thehoist pump through two screens to the hoist valve. The hoist systempressure can be tested at the two pressure taps (2).

The hoist system relief pressures are different in the RAISE and LOWERpositions.

The hoist system relief pressure during RAISE is:

17225 + 700 - 0 kPa (2500 + 100 - 0 psi)

The hoist system relief pressure during LOWER is:

3450 + 350 - 0 kPa (500 + 50 - 0 psi)

When the body is in the DOWN position, the hoist valve will be in theSNUB position. The body position sensor rod must be disconnected fromthe body and the sensor must be rotated to the RAISE position before theLOWER relief pressure can be tested.

In the HOLD, FLOAT and SNUB positions, the gauge will show thebrake cooling system pressure, which is a result of the restriction in thecoolers, brakes and hoses (normally much lower than the actual oil coolerrelief valve setting). The maximum pressure is limited by the oil coolerrelief valve, which has a setting of 790 ± 20 kPa (115 ± 3 psi).

2. Hoist systempressure taps

• Hoist pressuresduring LOWER

• Body position sensormust be in RAISE totest LOWER pressure

• Hoist pressuresduring RAISE

• Hoist pressuresduring HOLD, FLOATand SNUB

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21

Oil flows from the hoist pump through the hoist screens (1) to the hoistcontrol valve. Two hoist screen bypass switches (2) provide input signalsto the Transmission/Chassis ECM. The Transmission/Chassis ECM sendssignals to the VIMS, which informs the operator if the hoist screens arerestricted.

1. Hoist screens

2. Hoist screen bypassswitches

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1. Pump supply ports

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6

7

5

4 3

2

Oil flows from the hoist pump through two ports (1) (only one visible inthis view) to the hoist control valve located inside the right frame next tothe hoist cylinder. Two load check valves, one for each pump port, arelocated below the two plugs (2). The load check valves remain closeduntil the pump supply pressure is higher than the pressure in the hoistcylinders. The load check valves prevent the body from dropping beforethe RAISE pressure increases.

The hoist system relief pressures are different in the RAISE and LOWERpositions. The RAISE relief valve (3) controls the pressure in the hoistsystem during RAISE. The LOWER relief valve (4) controls the pressurein the hoist system during LOWER. The relief valve housing must beremoved to install shims (see Slide No. 164).

Oil flows through the drain port (5) to the hydraulic tank. When the hoistvalve is in the HOLD, FLOAT or SNUB position, all the hoist pump oilflows through two ports (6), one on each side of the hoist valve, to thetwo rear brake oil coolers located on the right side of the engine.

Brake cooling oil pressure can be checked at the test port (7) by removingthe plug and installing a pressure tap.

2. Load check valveplugs

3. RAISE relief valve

4. LOWER relief valve

5. Tank return port

6. Oil cooler port

7. Brake oil coolingpressure port

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1 3

6

5

4

7

2

A counterbalance valve (1) is mounted on the left side of the hoist valve.The counterbalance valve prevents cavitation of the cylinders when thebody raises faster than the pumps can supply oil to the cylinders (causedby a sudden shift of the load). The counterbalance valve signal pressurecan be checked at the test port (2) by removing the plug and installing apressure tap. The counterbalance signal pressure is equal to the RAISEpressure.

An oil cooler relief valve is located behind the large plug (3). The oilcooler relief valve limits the rear brake oil cooling pressure when the hoistvalve is in the HOLD, FLOAT or SNUB position. The setting of the oilcooler relief valve is 790 kPa (115 psi).

The hoist valve uses parking brake release pressure as the pilot oil to shiftthe directional spool inside the hoist valve. The parking brake releasepressure is 4700 ± 200 kPa (680 ± 30 psi).

Pilot pressure is always present at both ends of the directional spool. Twosolenoid valves are used to drain the pilot oil from the ends of thedirectional spool, which then allows the spool to move. On the left is theRAISE solenoid valve (4), and on the right is the LOWER solenoid valve(5).

3. Rear brake oil coolerrelief valve

1. Counterbalance valve

2. Counterbalance valvesignal pressure port

4. RAISE positionsolenoid valve

5. LOWER positionsolenoid valve

• Hoist pilot oil suppliedby parking brakesystem

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The RAISE and LOWER solenoid valves are always receivingapproximately 300 millivolts at a frequency of 80 Hz when they are inany position except HOLD. The excitation, referred to as "dither," is usedto keep the solenoids in a ready state for quick response.

When the Transmission/Chassis ECM receives an input signal from thehoist lever sensor, the Transmission/Chassis ECM sends an output signalcurrent between 0 and 1.9 amps to one of the solenoids. The amount ofcurrent sent to the solenoid determines the amount of pilot oil that isdrained from the end of the directional spool and, therefore, the distancethat the directional spool travels toward the solenoid.

Oil flows through two upper ports (6), one on each side of the hoist valve,to RAISE the hoist cylinders. Oil flows through two lower ports (7), oneon each side of the hoist valve, to LOWER the hoist cylinders.

• Hoist solenoidsreceive between 0 and 1.9 amps

6. RAISE port

7. LOWER port

• Hoist solenoids"dither" in HOLD

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• Hoist valve in HOLD

TOHOIST CYLINDER

ROD END

TOHOIST CYLINDER

HEAD END

TO REAR BRAKEOIL COOLERS

REAR BRAKEOIL COOLER

RELIEF VALVE

PARKING BRAKERELEASE PRESSURE

LOWERSOLENOID

RAISESOLENOID


PUMPSUPPLY PORT

TO TANK

LOW PRESSURERELIEF VALVE

HIGH PRESSURERELIEF VALVE

COUNTERBALANCEVALVE

"C" SERIESHOIST CONTROL VALVE

HOLD

DUAL STAGERELIEF VALVESIGNAL STEM

ROD ENDVENT SLOT

LOAD CHECKVALVE

Shown is a sectional view of the hoist valve in the HOLD position. Pilotoil pressure is directed to both ends of the directional spool. The spool isheld in the centered position by the centering springs and the pilot oil.Passages in the directional spool vent the dual stage relief valve signalstem to the tank. All the hoist pump oil flows through the rear brake oilcoolers to the rear brakes.

The position of the directional spool blocks the oil in the head end of thehoist cylinders. Oil in the rod end of the hoist cylinders is connected tothe rear brake cooling oil by a small vent slot cut in the directional spool.

A gauge connected to the hoist system pressure taps while the hoist valveis in the HOLD position will show the brake cooling system pressure,which is a result of the restriction in the coolers, brakes and hoses(normally much lower than the actual oil cooler relief valve setting). Themaximum pressure in the circuit should correspond to the setting of thefront brake oil cooler relief valve. The setting of the oil cooler relief valveis 790 kPa (115 psi).

• Hoist supply oil flowsto rear brake cooling

• Test brake coolingpressure at pumps inHOLD

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• Hoist valve in RAISE

FROM HOIST CYLINDERROD END

TO HOIST CYLINDERHEAD END



RELIEF VALVE

PUMPSUPPLY PORT

TO TANK



COUNTERBALANCEVALVE

RAISE


ROD ENDVENT SLOT

LOAD CHECKVALVE


LOWERSOLENOID


RAISESOLENOID


Shown is a sectional view of the hoist valve in the RAISE position. TheRAISE solenoid is energized and drains pilot oil pressure from the lowerend of the directional spool. The directional spool moves down. Pumpoil flows past the directional spool to the head end of the hoist cylinders.

When the directional spool is initially shifted, the two load check valves(one shown) remain closed until the pump supply pressure is higher thanthe pressure in the hoist cylinders. The load check valves prevent thebody from dropping before the RAISE pressure increases.

The directional spool also sends hoist cylinder raise pressure to the dualstage relief valve signal stem and the counterbalance valve. The dualstage relief valve signal stem moves down and blocks the supply pressurefrom opening the low pressure relief valve.

• Load check valve

• Dual stage reliefsignal stem

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The counterbalance valve is held open by the hoist cylinder raise pressure.Oil from the rod end of the hoist cylinders flows freely to the rear brakeoil coolers. If the body raises faster than the pump can supply oil to thehoist cylinders (caused by a sudden shift of the load) and the raisepressure drops below 2275 kPa (330 psi), the counterbalance valve startsto close and restricts the flow of oil from the rod end of the hoistcylinders. Restricting the flow of oil from the rod end of the hoistcylinders will slow down the cylinders and prevent cavitation. Cavitationin the hoist cylinders can cause the body to drop suddenly when the hoistlever is moved from the RAISE position to the LOWER position.

The pressure in the head end of the hoist cylinders cannot exceed:

17225 + 700 - 0 kPa (2500 + 100 - 0 psi)

The high pressure relief valve will open if the pressure increases abovethis specification. When the high pressure relief valve opens, the dumpspool moves to the left, and pump oil is directed to the rear brake oilcoolers.

The high pressure hoist relief valve setting is checked at the two pressuretaps located on the hoist pump. Check the relief pressures with the hoistlever in the RAISE position and the engine at HIGH IDLE.

• High pressure reliefsetting checkedduring RAISE at HIGHIDLE

• Counterbalance valve

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• Counterbalance valve

RAISE

HEAD ENDSIGNAL PRESSURE

FROMHOIST CYLINDER

ROD END

TO TANK

LOWER AND FLOAT

TOHOIST CYLINDER

ROD END

FROMPUMP

CHECK VALVE

HOISTCOUNTERBALANCE

VALVE

ROD ENDPRESSURE

PISTON

During RAISE, the counterbalance valve prevents the dump body fromrunning ahead of the hoist pumps if the load shifts rapidly to the rear ofthe body and attempts to pull the hoist cylinders. Signal pressure from thehead end of the hoist cylinders holds the counterbalance valve open. Oilfrom the rod end of the hoist cylinders flows unrestricted through thecounterbalance valve to the tank. If the head end pressure decreasesbelow 2270 kPa (330 psi), the counterbalance valve moves down andrestricts the flow of oil from the rod end of the cylinders to the tank.

If no head end signal pressure is present, rod end pressure can still openthe counterbalance valve. If the rod end pressure exceeds 6900 ± 690 kPa(1000 ± 100 psi) at the rod end pressure piston, the valve will move upand allow rod end oil to flow from the cylinders to the tank.

During LOWER and FLOAT, the counterbalance valve allowsunrestricted flow from the pump through a check valve to the rod end ofthe hoist cylinders.

• Head end signalpressure holds valveopen

• Rod end pressure canopen valve

• No restriction inLOWER and FLOAT

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• Hoist valve in LOWER(power down)

TO HOIST CYLINDERROD END

FROM HOIST CYLINDERHEAD END



RELIEF VALVE

PUMPSUPPLY PORT

TO TANK



COUNTERBALANCEVALVE


ROD ENDVENT SLOT

LOAD CHECKVALVE

LOWERSOLENOID

RAISESOLENOID

LOWER (POWER DOWN)




Shown is a sectional view of the hoist valve in the LOWER (power down)position. The LOWER solenoid is energized and drains pilot oil pressurefrom the upper end of the directional spool. The directional spool movesup.

Supply oil from the pump flows past the directional spool, through thecounterbalance valve, to the rod end of the hoist cylinders. Oil in the headend of the hoist cylinders flows to the tank. The supply oil in the rod endof the cylinders and the weight of the body move the cylinders to theirretracted positions.

Just before the body contacts the frame, the body position sensor sends asignal to the Transmission/Chassis ECM to move the valve spool to theSNUB position. In the SNUB position, the valve spool moves slightly torestrict the flow of oil and lower the body gently.

• Body position sensorcontrols SNUBposition

- 203 -

• Dual stage reliefsignal stem

STMG 70611/98

The directional spool also vents the passage to the dual stage relief valvesignal stem. The dual stage relief valve signal stem allows supplypressure to be limited by the low pressure relief valve.

If the pressure in the rod end of the hoist cylinders exceeds 3450 + 350 - 0 kPa (500 + 50 - 0 psi), the low pressure relief valve willopen. When the low pressure relief valve opens, the dump spool movesto the left and pump oil flows to the rear brake oil coolers.

The low pressure hoist relief valve setting is checked at the two pressuretaps located on the hoist pump. Check the relief pressures with the hoistlever in the LOWER position and the engine at HIGH IDLE.

When the body is in the DOWN position, the hoist valve will be in theSNUB position. The body position sensor rod must be disconnected fromthe body, and the sensor must be rotated to the RAISE position before theLOWER relief pressure can be tested.

• Test low pressurerelief setting duringLOWER at HIGH IDLE

• Body position sensormust be in RAISE totest LOWER pressure

168

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• Hoist valve in FLOAT

TO HOISTCYLINDERROD END

FROM HOISTCYLINDERHEAD END



RELIEF VALVE

PUMPSUPPLY PORT

TO TANK



COUNTERBALANCEVALVE

FLOAT


ROD ENDVENT SLOT

LOAD CHECKVALVE

LOWERSOLENOID

RAISESOLENOID




Shown is a sectional view of the hoist valve in the FLOAT position. TheLOWER solenoid is partially energized and drains part of the pilot oilpressure above the directional spool to the tank. The directional spoolmoves up. Because the pilot pressure is only partially drained, thedirectional spool does not move as far up as during LOWER.

Pump supply oil flows past the directional spool, through thecounterbalance valve, to the rod end of the hoist cylinders. Oil in the headend of the hoist cylinders flows to the tank. The directional valve is in aposition that permits the pressure of the oil flowing to the rear brake oilcoolers to be felt at the rod end of the hoist cylinders.

The truck should normally be operated with the hoist lever in the FLOATposition. Traveling with the hoist in the FLOAT position will make surethe weight of the body is on the frame and body pads and not the hoistcylinders. The hoist valve will actually be in the SNUB position.

Just before the body contacts the frame, the body position sensor sends asignal to the Transmission/Chassis ECM to move the valve spool to theSNUB position. In the SNUB position, the valve spool moves slightly torestrict the flow of oil and lower the body gently.

• Operate truck withhoist lever in FLOAT

• Valve moves to SNUBposition

- 205 -

• Two-stage hoistcylinders

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STMG 70611/98

Shown are the twin two-stage hoist cylinders used to raise and lower thebody.

Check the condition of the body pads (arrow) for wear or damage.

To LOWER the body with a dead engine, hoist pilot pressure is required.The towing pump can be used to provide the hoist pilot oil. To lower thebody with a dead engine:

- Turn ON the key start switch so the towing motor and the hoistsolenoids can be energized.

- Move the hoist lever to the RAISE position for 15 seconds, then tothe FLOAT position.

- Depress the brake retraction switch on the dash (see Slide No. 48).

To RAISE the body with a dead engine, connect an Auxiliary Power Unit(APU) to the hoist cylinders. Follow the same procedure used to lowerthe body with a dead engine, except keep the hoist lever in RAISE afterthe 15 seconds interval.

NOTE: For more information on using the APU, refer to the SpecialInstructions "Using 1U5000 Auxiliary Power Unit (APU)"(Form SEHS8715) and "Using the 1U5525 Attachment Group"(Form SEHS8880).

• Body pads (arrow)

• Body lower with deadengine

• Body raise with deadengine

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• Hoist system

TO HOIST CYLINDERHEAD END

TO HOIST CYLINDERROD END

FROM PARKINGBRAKE RELEASE

VALVE

HOIST PUMP HOISTSCREENSSUCTION

SCREENS

HOIST SYSTEMHOLD


REARBRAKES

PILOT OIL

The hoist system pumps pull oil from the hydraulic tank through suctionscreens.

Oil flows from the hoist pump through the hoist screens to the hoistcontrol valve.

The hoist valve uses parking brake release pressure as pilot oil to shift thedirectional spool inside the hoist valve. Two solenoid valves are used todrain the pilot oil from the ends of the directional spool. The solenoidvalve on the left is energized in the RAISE position. The solenoid valveon the right is energized in the LOWER or FLOAT position.

When the hoist valve is in the HOLD or FLOAT position, all the hoistpump oil flows through the rear brake oil coolers to the rear brakes.

- 207 -STMG 70611/98

An oil cooler relief valve is located in the hoist valve. The relief valvelimits the rear brake oil cooling pressure when the hoist valve is in theHOLD or FLOAT position.

Two hydraulic cylinders are used to raise the body away from the frameof the truck. When the hoist lever is held in the RAISE position, supplyoil flows to the head end of the hoist cylinders and moves the two stagecylinders to their extended lengths. The oil from the rod end of thecylinders flows through the hoist valve to the rear brake oil coolingcircuit.

When the hoist lever is moved to the LOWER or FLOAT position and thecylinders are extended, supply oil enters the rod end of the hoist cylindersand lowers the second stage of the cylinders. The oil from the head endof the cylinders flows through the hoist valve to the hydraulic tank.

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AIR SYSTEM AND BRAKES

789C

AIR SYSTEM AND BRAKES

Two separate brake systems are used on the "C" Series trucks. The twobrake systems are: the parking/secondary brake system and theservice/retarder brake system.

The parking/secondary brakes are spring engaged and hydraulicallyreleased. The service/retarder brakes are engaged hydraulically by an air-over-oil brake system.

The "C" Series trucks are also equipped with an air system. An enginedriven air compressor supplies the air and fills two tanks. Air from thetanks provides energy to perform several functions:

- Engine start-up

- Service and retarder brake control

- Secondary and parking brake control

- Automatic lubrication injection (grease)

- Horn, air seat and cab clean-out

• Two brake systems:

- Parking/secondarybrake system

- Service/retarderbrake system

• Air system functions

- 209 -

• Oil cooled brakeassembly

• Seals prevent oil leaksor transfer

172

STMG 70611/98

Shown is a cutaway illustration of an oil cooled brake assembly. Thebrakes are environmentally sealed and adjustment free. Oil continuallyflows through the brake discs for cooling. Duo-Cone seals prevent thecooling oil from leaking to the ground or transferring into the axlehousing. The wheel bearing adjustment must be maintained to keep theDuo-Cone seals from leaking.

The smaller piston (yellow) is used to ENGAGE the secondary andparking brakes. The parking brakes are spring ENGAGED andhydraulically RELEASED.

The larger piston (purple) is used to ENGAGE the retarder/service brakes.The retarder/service brakes are engaged hydraulically by an air-over-oilbrake system.

• Small pistonENGAGES secondaryand parking brakes

• Large pistonENGAGESretarder/servicebrakes

- 210 -

• 789C air compressor

173

STMG 70611/98

Air Charging System

The air system is charged by an air compressor mounted on the left frontof the engine. Shown is the 789C four-cylinder air compressor. The785C has a two-cylinder air compressor.

System pressure is controlled by the governor (arrow). The governormaintains the system pressure between 660 and 830 kPa (95 and 120 psi).

The governor setting can be adjusted with a screw below the cover on topof the governor. Turn the adjustment screw OUT to increase the pressureand IN to decrease the pressure.

The capacity of the air charging system on the 789C truck has beenincreased. The 789C air compressor has been increased from a two-cylinder compressor to a four-cylinder compressor. To handle theincreased air flow, two larger air dryers are used, and the hoses and tubinghave also been increased in size.

• Air compressorgovernor (arrow)

• Air compressorgovernor adjustment

• 789C has increasedair charging capacity

- 211 -

1. 789C air dryers

• 785C has one air dryer

174

STMG 70611/98

1

1

2

On the 789C truck, air flows from the air compressor to two air dryers (1)located behind the left front tire. The 785C has one air dryer located infront of the left front suspension cylinder.

The air system can be charged from a remote air supply through a groundlevel connector (2) inside the left frame.

The air dryers remove contaminants and moisture from the air system.The condition of the desiccant in the air dryers should be checked every250 hours and changed periodically (determined by the humidity of thelocal climate).

When the air compressor governor senses that system air pressure is at thecut-out pressure of 830 kPa (120 psi), the governor sends an air pressuresignal to the purge valve in the bottom of the dryers. The purge valveopens and air pressure that is trapped in the air dryers is exhaustedthrough the desiccant, an oil filter and the purge valve.

An air system relief valve is located on the air dryers to protect the systemif the air compressor governor malfunctions.

A heating element in the bottom of the dryers prevents moisture in thedryers from freezing in cold weather.

• Air system relief valve

• Purge valve

2. Remote air supplyconnector

• Check desiccant

• Heating element

- 212 -

1. Service/retarderbrake tank

175

STMG 70611/98

2

1

Air flows through the air dryers and fills two tanks. The service/retarderbrake tank (1) is located on the right platform. This tank also supplies airfor the air start system.

The second tank is located behind the cab and supplies air for theparking/secondary brake system.

Condensation should be drained from the tank daily through the drainvalve (2).

A relief valve located near the tank drain is installed in theservice/retarder brake tank. This relief valve protects the air system whenthe air dryers have exhausted and the ball check valves in the air dryeroutlet ports close. The check valves separate the air system from the airdryer relief valves.

2. Condensation drainvalve

• Relief valve (notshown)

- 213 -

1. Pressure protectionvalve

176

STMG 70611/98

1

2

Located behind the operator’s station is a pressure protection valve (1).Supply air flows from the large service/retarder brake tank, through thepressure protection valve, to the secondary air system and accessories.The pressure protection valve opens at 550 kPa (80 psi) and closes at482 kPa (70 psi). If the secondary air lines or an accessory circuit fails,the pressure protection valve maintains a minimum of 482 kPa (70 psi) inthe service/retarder brake circuit.

To test the pressure protection valve, drain the air pressure toapproximately 345 kPa (50 psi). Use the VIMS display to observe thebrake air pressure. With the engine running at LOW IDLE, press the hornbutton. Record the air pressure when the horn sounds. This pressurereading is the open setting of the pressure protection valve. Slowly drainthe air pressure and record the air pressure when the horn turns off. Thispressure reading is the setting of the pressure protection valve when itcloses.

The air system pressure sensor (2) provides an input signal to the BrakeECM. The Brake ECM sends a signal to the VIMS, which informs theoperator if a problem exists in the air system.

Also located behind the operator’s station are the service/retarder brakeswitch, the parking/secondary brake switch and the brake light switch (see Slide No. 128).

2. Air system pressuresensor

• Pressure protectionvalve test

• Other air switchesbehind cab

- 214 -

177

STMG 70611/98

The solenoid air valve (arrow) provides a controlled air supply for theautomatic lubrication (grease) system. The solenoid air valve iscontrolled by the VIMS. The VIMS ENERGIZES the solenoid tenminutes after the machine is started. The VIMS keeps the solenoidENERGIZED for 75 seconds and then DE-ENERGIZES it. Every 60 minutes thereafter, the VIMS ENERGIZES the solenoid for 75seconds until the machine is stopped (turned off). These settings areadjustable through the VIMS keypad in the cab.

• Automatic lubricationsolenoid air valve(arrow)

- 215 -

• Parking/secondarybrake tank

178

STMG 70611/98

Located behind the operator’s station is the parking/secondary brake airtank. A drain valve is located on the right side of the cab. Moistureshould be drained from the tank daily through the drain valve (see Slide No. 33).

A check valve (arrow) prevents a loss of air if an air line breaks upstreamof the air tank.

• Check valve (arrow)

179

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• 789C air chargingsystem

AIR COMPRESSORAND GOVERNOR

AIRDRYERS

PRESSUREPROTECTION

VALVE

SERVICE/RETARDERBRAKE TANK

PARKING/SECONDARYBRAKE TANK

LOW AIRSENSORTO AUTO LUBE SOLENOID

TO HORN / SEAT / CLEAN-OUT

TO AIR STARTSOLENOID

789C AIR CHARGING SYSTEM

REMOTESUPPLY

This schematic shows the flow of air through the 789C air chargingsystem. Air flows from the air compressor, through the two air dryers, tothe service/retarder brake tank.

The 785C air charging system is the same as the 789C, but has only oneair dryer.

Air from the service/retarder brake tank enters the pressure protectionvalve. When the pressure in the service/retarder tank reaches 550 kPa (80 psi), the pressure protection valve allows air to flow to theparking/secondary brake tank, the air start system, the automaticlubrication system and the accessory circuits (horn, air seat and cab clean-out).

All tanks have a check valve at the air supply port to prevent a loss of airif a leak upstream of the tank occurs.

• 785C has one air dryer

- 217 -

180

STMG 70611/98

Brake Systems

The manual retarder valve (arrow) is controlled by the retarder lever inthe cab. Normally, the retarder valve blocks air flow to the service brakerelay valve near the brake master cylinders and to the front brake oilcooler diverter valve.

When the retarder lever is pulled down, air flows to the service brakerelay valve and the front brake oil cooler diverter valve [maximumpressure is 550 kPa (80 psi)]. The retarder lever is used to modulate theservice brake engagement by metering the amount of air flow to theservice brake relay valve.

The retarder engages the same brakes as the service brake pedal (see SlideNo. 43), but is easier to control for brake modulation.

• Manual retarder valve(arrow)

- Engages all fourservice brakes

- Modulates brakesbetter than pedal

- 218 -

1. Service brake valve

2. Automatic RetarderControl (ARC) valve

3. Air supply manifold

181

STMG 70611/98

3

5

4

2

681 7

The service brake valve (1) is controlled by the brake pedal in the cab.Supply air for the service brake valve, the manual retarder valve and theAutomatic Retarder Control (ARC) valve (2) is supplied from themanifold (3).

When the service brakes are engaged, air flows from the service brakevalve to the service brake relay valve near the brake master cylinders andto the front brake oil cooler diverter valve [maximum pressure is 825 kPa (120 psi)].

The service brake valve engages the same brakes as the retarder, but doesnot control brake modulation as precisely as the retarder.

Air from the service brake valve and the manual retarder valve flowsthrough the double check valve (4) to the service brake relay valve andthrough the double check valve (5) to the front brake oil cooler divertervalve. If the manual retarder and the service brakes are engaged at thesame time, air from the system with the highest pressure will flowthrough the double check valves to the service brake relay valve and tothe front brake oil cooler diverter valve.

Air from the manual retarder valve also flows through the double checkvalve (6) to the retarder switch (7). The retarder switch turns on theamber retarder lamp on the dash in the operator’s station when the manualretarder is ENGAGED (see Slide No. 47).

4. Double check valveto brake relay

5. Double check valveto front coolerdiverter valve

• System with highestpressure engagesbrakes

6. Double check valve

7. Retarder switch

- 219 -STMG 70611/98

The function of the Automatic Retarder Control (ARC) system is tomodulate truck braking (retarding) when descending a long grade tomaintain a constant engine speed.

When the ARC is engaged, air flows from the ARC valve to a separateARC relay valve located near the brake master cylinders. Air also flowsfrom the ARC valve through the double check valve (6) to the retarderswitch (7) and through double check valve (5) to the front brake oil coolerdiverter valve.

The brake light switch and the service/retarder brake switch (see SlideNo. 128) are located in the supply line to the front brake oil coolerdiverter valve (see Slide No. 102). The service brake valve, the manualretarder valve and the Automatic Retarder Control (ARC) valve send airto these switches when engaged.

The secondary brake valve (8) is controlled by the red pedal in the cab(see Slide No. 43). When the secondary brakes are engaged, air flowsfrom the secondary brake valve to the signal port of an inverter valve (seenext slide). The inverter valve then blocks the flow of air from thesecondary brake tank to the brake release valve (see Slide No. 183).

Blocking the air from the brake release valve positions the spool in thebrake release valve to drain the oil from the parking brakes, which allowsthe springs in the parking brake to ENGAGE the brakes. The secondarybrake valve can be used to modulate parking brake engagement bymetering the amount of air flow to the brake release valve.

The parking brake air valve (see Slide No. 44) on the shift console in thecab also controls the flow of air to the brake release valve, but the parkingbrake air valve does not modulate the parking brake application.

The parking/secondary brake switch (see Slide No. 128) is located in thesupply line to the brake release valve. The secondary brake valve and theparking brake air valve send air to this switch when engaged.

INSTRUCTOR NOTE: The ARC system will be discussed in moredetail later in this presentation.

• ARC engagesseparate relay valve

• Brakes, retarder andARC activate brakeswitches

• Secondary andparking brake valvesactivate brake switch

8. Secondary brakevalve

- Modulates parkingbrake engagement

• Parking brake valvedoes not modulateengagement

- 220 -

182

STMG 70611/98

2

1

When the secondary brakes are engaged, air flows from the secondarybrake valve to the signal port (1) of the inverter valve (2). The invertervalve then blocks the flow of air from the secondary brake tank to thebrake release valve.

Blocking the air from the brake release valve positions the spool in thebrake release valve to drain the oil from the parking brakes, which allowsthe springs in the parking brake to ENGAGE the brakes.

1. Inverter valve signalport

2. Inverter valve

- 221 -

183

STMG 70611/98

1

4

5

2

3

Oil from the parking brake release pump (see Slide No. 98) flows throughthe parking brake release filter (see Slide No. 101) to the brake releasevalve (1) located inside the left frame near the torque converter. Oil flowsfrom the parking brake release valve to the parking brake piston in thebrakes when the parking brakes are released.

Supply air from the parking brake air valve in the cab or the secondarybrake valve flows through the small hose (2) to an air chamber in thebrake release valve. The brake release valve contains an air piston thatmoves a spool. The spool either directs oil to RELEASE the parkingbrakes or drains oil to ENGAGE the parking brakes. A relief valve (3) inthe brake release valve limits the system pressure for releasing the brakes.The setting of the relief valve is 4700 ± 200 kPa (680 ± 30 psi).

Supply oil flows from the brake release valve through an orifice and ascreen (4) to the brake oil makeup tank.

To release the parking brakes for service work or towing, the electricmotor that turns the towing pump (5) can be energized by the brakerelease switch located in the cab (see Slide No. 48). The pump sends oilto the brake release valve to RELEASE the parking brakes. Towingpump pressure is controlled by a relief valve in the towing pump.

4. Brake makeup tanksupply oil screen

1. Brake release valve

2. Brake release valveair supply hose

3. Brake release reliefvalve

5. Towing pump

184

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PARKING BRAKERELEASE VALVE

TOWING PUMPAND MOTOR

PARKINGBRAKE

RELEASEPUMP

TOWING PUMPRELIEF VALVE

CHECKVALVE

TO HOISTPILOT

SYSTEM

RELIEFVALVE

TOTC LOCKUP

VALVEPARKING

BRAKERELEASE

FILTER

FROM CAB SECONDARYOR PARKING BRAKE VALVE

TOWING SYSTEM

Normally, supply oil flows from the parking brake release pump, throughthe parking brake release filter, to the parking brake release valve. If airpressure is present from the parking brake air valve or the secondarybrake valve, supply oil flows past the relief valve, the check valve and thespool to RELEASE the parking brakes. The relief valve limits the systempressure for releasing the brakes, torque converter lockup and for the pilotoil to shift the hoist valve. The setting of the relief valve in the parkingbrake valve is 4700 ± 200 kPa (680 ± 30 psi).

This schematic shows the flow of oil through the parking brake releasesystem when the towing system is activated.

Oil flow from the parking brake release pump has stopped. The towingmotor is energized, and air pressure is present above the parking brakerelease valve piston. The air pressure moves the spool in the parkingbrake release valve down to block the drain port.

• Parking brake releasesystem during towing

• Parking brake reliefvalve limits TC lockupand hoist pilotpressure

• Normal parking andsecondary brakeoperation

- 223 -STMG 70611/98

Oil flows from the towing pump to the parking brake release valve andthe parking brakes. The check valve to the right of the parking brakerelease filter blocks the oil from the towing pump from flowing to theparking brake release pump.

During towing, the parking brake release pressure is limited by a reliefvalve in the towing pump. When the relief valve opens, oil transfers fromthe pressure side to the suction side of the towing pump. The setting ofthe relief valve is approximately 4480 kPa (650 psi).

A check valve in the outlet port of the towing pump prevents oil fromflowing to the towing pump during normal operation.

To check the brake release system used for towing, connect a gauge to theparking brake release pressure tap on the rear axle (see Slide No. 189).Use a long gauge hose so the gauge can be held in the cab. With theparking brake air valve in the RELEASE position and the key start switchin the ON position, energize the parking brake release switch used fortowing (on the dash). The parking brake release pressure should increaseto 4480 kPa (650 psi). Turn off the switch when the pressure stopsincreasing.

The parking brake release pressure must increase to a minimum of 3790 kPa (550 psi). The parking brakes start to release between 3100 and 3445 kPa (450 and 500 psi). During towing, the brake releaseswitch on the dash must be energized whenever the parking brake releasepressure decreases below this level or the brakes will drag. The parkingbrakes are fully released between 3445 and 3860 kPa (500 and 560 psi).

NOTE: A minimum of 550 kPa (80 psi) air pressure must beavailable at the parking brake release valve to ensure full release ofthe brakes for towing.

NOTICE

Activate the brake release switch only when additional pressure isrequired to release the brakes. Leaving the brake release (towing)motor energized continuously will drain the batteries.

The parking brake release pressure setting must not exceed5445 kPa (790 psi). Exceeding this pressure can cause internaldamage to the brake assembly.

• Procedure to checktowing system

• Towing pump checkvalve

• Relief valve in towingpump limits brakerelease pressure

• Parking brake releasepressures

185

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• Parking/secondarybrake system

PARKINGBRAKEVALVE

SECONDARYBRAKEVALVE

PARKINGBRAKE

RELEASEVALVE

PARKING/SECONDARY BRAKES

PARKING BRAKES ENGAGED

TO TC LOCKUP VALVEAND HOIST

PILOT SYSTEM

PARKINGBRAKE

RELEASEPUMP

SECONDARY BRAKES RELEASED

PARKING / SECONDARYBRAKE TANK

PARKING /SECONDARY

BRAKESWITCH

INVERTERVALVE

Shown is the parking/secondary brake hydraulic and air system with thesecondary brakes RELEASED and the parking brakes ENGAGED.Supply air from the parking/secondary brake air tank flows to thesecondary brake valve and is blocked from flowing to the inverter valvesignal port. Supply air is allowed to flow through the inverter valve and isblocked by the parking brake air valve.

No air pressure is present to move the spool in the parking brake releasevalve. Supply oil from the parking brake release pump is blocked by thespool. Oil from the parking brake is open to drain through the parkingbrake release valve, which allows the springs in the parking brake toENGAGE the brakes.

A parking/secondary brake switch is located in the air line between theparking brake valve and the parking brake release valve. The switchprovides an input signal to the Transmission/Chassis ECM. When theparking or secondary brakes are ENGAGED, the switch signals theTransmission/Chassis ECM to allow rapid downshifts.

• Parking/secondarybrake switch input toTransmission/ChassisECM

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1. Service brake andmanual retarder relayvalve

2. ARC relay valve

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1

33 6

4 5 2

The front service brake relay valve (1) receives metered air from only theservice brake valve or the manual retarder valve. The rear AutomaticRetarder Control (ARC) brake relay valve (2) receives metered air fromonly the ARC valve.

When the service brakes or manual retarder brakes are ENGAGED, thefront relay valve opens and metered air flows from the service brake tank,through the double check valves (3), to the three brake cylinders (4). Thebrake relay valves reduce the time required to engage and release thebrakes. The double check valves (3) are used to separate the service andmanual retarder brakes from the ARC brake system.

When the ARC brake system is ENGAGED, the rear relay valve opensand metered air flows from the service brake tank, through a pressureprotection valve (5) and the double check valves (3), to the three brakecylinders (4). The pressure protection valve prevents a total loss of airpressure in the service brake air system if the ARC relay valve fails. Theprotection valve opens to send flow to the ARC relay valve at 380 kPa (55 psi) and closes when the pressure decreases below 310 kPa (45 psi).

The brake cylinders operate by air-over-oil. When the metered air entersthe brake cylinders, a piston moves down and pressurizes the oil in thebottom of the cylinders. One brake cylinder supplies oil to the frontbrakes through the slack adjuster (6). Two brake cylinders supply oil tothe rear brakes through a separate slack adjuster.

5. Pressure protectionvalve

• Relay valves reducebraking time

• Double check valvesseparate systems

3. Double check valves

4. Brake cylinders

6. Front brake slackadjuster

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187

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1

32

5

4

As the brake discs in the brake assemblies wear, more oil is needed fromthe brake cylinders to compensate for the wear. The brake makeup oiltank (1) supplies makeup oil for the brake cylinders. Oil from the parkingbrake release valve flows through an orifice and the screen (2) to providea continuous supply of oil to the makeup tank. Low flow to the makeuptank can cause the makeup oil reserve to decrease and cause the brakecylinders to overstroke.

To check for makeup oil flow, remove the cover from the makeup oiltank. With the engine at HIGH IDLE, a stream of oil filling the tankshould be visible. If a stream of oil is not visible, the filter or hose to thetank may be restricted or pump flow may be low.

Keep the service brake ENGAGED for at least one minute. If air is in thesystem or a loss of oil downstream from the cylinders occurs, the piston inthe cylinder will overstroke and cause an indicator rod to extend and openthe brake overstroke switch (3). The switch provides an input signal tothe Brake ECM. The Brake ECM sends the signal to the VIMS, whichinforms the operator of the condition of the service/retarder brake oilcircuit. If an overstroke condition occurs, the problem must be repairedand the indicator rod pushed in to end the warning.

1. Brake oil makeuptank

2. Brake oil makeuptank supply screen

• Check brake makeupoil flow

3. Brake overstrokeswitch

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Front brake oil pressure can be measured at the pressure tap (4) located onthe front brake slack adjuster.

The oil-to-air ratio of the brake cylinder is approximately 6.6 to 1. To testthe brake cylinder, install a gauge in the fitting on top of the brakecylinder and a gauge on the pressure tap on the slack adjuster. When theservice brakes are ENGAGED, if the air pressure in the brake cylinder is690 kPa (100 psi), the oil pressure measured at the slack adjuster shouldbe approximately 4560 kPa (660 psi). When the brakes are RELEASED,both pressures should return to zero.

Inspect the condition of the breather (5) for the brake cylinders. Oilshould not leak from the breathers. Oil leaking from the breathers is anindication that the oil piston seals in the brake cylinder need replacement.Air flow from the breathers during a brake application is an indicationthat the brake cylinder air piston seals need replacement.

• Brake cylinder test

4. Front brake oilpressure tap

5. Brake cylinderbreather

188

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• Brake cylinderENGAGED

AIRPISTON

RODSPRING

INDICATOR ROD

AIRINLET

BRAKE CYLINDERBRAKES ENGAGED

VALVE

OILPISTON

FROMMAKEUP

TANK

TOSLACK

ADJUSTER

This slide shows a sectional view of the brake cylinder when the brakesare ENGAGED.

Air pressure from the brake relay valve enters the air inlet. The airpressure moves the air piston and the attached rod closes the valve in theoil piston. When the valve in the oil piston is closed, the oil pistonpressurizes the oil in the cylinder. The pressure oil flows to the slackadjuster.

If air is in the system or a loss of oil downstream from the cylindersoccurs, the piston in the cylinder will overstroke, which causes theindicator rod to extend and open the brake overstroke switch. If anoverstroke condition occurs, the problem must be repaired and theindicator rod pushed in to end the warning.

When the air pressure is removed from behind the air piston, the springmoves the air piston and the attached rod opens the valve in the oil piston.Any makeup oil that is needed flows into the passage at the top of the oilchamber, through the valve, and into the oil chamber at the right of the oilpiston.

• Overstroke switchindicates oil loss

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1. Slack adjuster

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1

23 3

The truck is equipped with two slack adjusters--one for the front brakesand one for the rear brakes. The slack adjuster (1) shown is for the rearbrakes. The slack adjusters compensate for brake disc wear by allowing asmall volume of oil to flow through the slack adjuster and remain betweenthe slack adjuster and the brake piston under low pressure. The slackadjusters maintain a slight pressure on the brake piston at all times.

Brake cooling oil pressure maintains a small clearance between the brakediscs.

The service brake oil pressure can be measured at the two taps (2) locatedon top of the slack adjusters.

Air can be removed from the service brakes through two remote bleedvalves (not shown) mounted on the rear axle housing.

The parking brake release pressure can be measured at the two taps (3) onthe axle housing.

NOTE: Air can be removed from the front service brakes throughbleed valves located on each wheel.

• Cooling oil pressuremaintains clearancebetween discs

2. Service brakepressure taps

• Service brake bleedvalves

3. Parking brake releasepressure taps

190

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• Slack adjusterRELEASED andENGAGED

• Large piston moves toENGAGE brakes

• Small piston allowsmakeup oil to brakes

OIL FLOWTO BRAKECYLINDER

OIL FLOWFROM BRAKE

CYLINDER

FROMWHEELBRAKES

TOWHEELBRAKES

TOWHEELBRAKES

BRAKES ENGAGEDBRAKES RELEASED

LARGE PISTON

SMALL PISTON

FROMWHEELBRAKES

BRAKE SLACK ADJUSTER

This slide shows sectional views of the slack adjuster when the brakes areRELEASED and ENGAGED.

When the brakes are ENGAGED, oil from the brake cylinders enters theslack adjusters and the two large pistons move outward. Each large pistonsupplies oil to one wheel brake. The large pistons pressurize the oil to theservice brake pistons and ENGAGE the brakes.

Normally, the service brakes are FULLY ENGAGED before the largepistons in the slack adjusters reach the end of their stroke. As the brakediscs wear, the service brake piston will travel farther to FULLYENGAGE the brakes. When the service brake piston travels farther, thelarge piston in the slack adjuster moves farther out and contacts the endcover. The pressure in the slack adjuster increases until the small pistonmoves and allows makeup oil from the brake cylinders to flow to theservice brake piston.

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When the brakes are RELEASED, the springs in the service brakes pushthe service brake pistons away from the brake discs. The oil from theservice brake pistons pushes the large pistons in the slack adjuster to thecenter of the slack adjuster. Makeup oil that was used to ENGAGE thebrakes is replenished at the brake cylinders from the makeup tank.

The spring behind the large piston causes some oil pressure to be felt onthe service brake piston when the brakes are RELEASED. Keeping somepressure on the brake piston provides rapid brake engagement with aminimum amount of brake cylinder piston travel.

The slack adjusters can be checked for correct operation by opening theservice brake bleed screw with the brakes RELEASED. A small amountof oil should flow from the bleed screw when the screw is opened. Thesmall flow of oil verifies that the spring behind the large piston in theslack adjuster is maintaining some pressure on the service brake piston.

Another check to verify correct slack adjuster operation is to connect agauge to the pressure tap on top of the slack adjuster and another gauge atthe service brake bleed screw location. With system air pressure atmaximum and the service brake pedal depressed, the pressure reading onboth gauges should be approximately the same.

When the brakes are RELEASED, the pressure at the slack adjustershould return to zero. The pressure at the service brake bleed screwlocation should return to the residual pressure held on the brakes by theslack adjuster piston.

The residual pressures at the service brake bleed screw location shouldbe:

785C front: 103 kPa (14.9 psi) 785C rear: 59 kPa (8.6 psi)

789C front: 106 kPa (15.3 psi) 789C rear: 65 kPa (9.5 psi)

Low residual pressure indicates a failed slack adjuster. High residualpressure may indicate a failed slack adjuster or warped brake discs. Tocheck for warped brake discs, rotate the wheel to see if the pressurefluctuates. If the pressure fluctuates while rotating the wheel, the brakediscs are probably warped and should be replaced.

To check for brake cooling oil leakage, block the brake cooling ports andpressurize each brake assembly to a maximum of 138 kPa (20 psi). Closeoff the air supply source and observe the pressure trapped in the brakeassembly for five minutes. The trapped pressure should not decrease.

• Large piston springkeeps pressure onservice brake piston

• Check slack adjusterfor correct operation

• Brakes ENGAGED--pressures should beequal

• Brakes RELEASED--residual pressure atbleed screw

• Check for warpedbrake discs

• Check for brakecooling oil leakage

• Brake springs movelarge pistons to centerof slack adjuster

191

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SERVICERELAYVALVE

SERVICEBRAKE VALVE

RETARDERVALVE

BRAKE CYLINDERS

ARCVALVE

SERVICE/RETARDER BRAKE AIR SYSTEMSERVICE BRAKES ENGAGED

ARCRELAYVALVE

BRAKELIGHTAND

SERVICE /RETARDER

SWITCH

RETARDERSWITCH

FRONT BRAKE COOLERDIVERTER VALVE

PRESSUREPROTECTION

VALVE

This schematic shows the flow of air through the service/retarder brake airsystem when the retarder (manual and automatic) is RELEASED, and theservice brakes are ENGAGED. Supply air pressure flows from the largeservice brake air tank to the relay valves and the service brake valve,manual retarder valve and the ARC valve.

The manual retarder valve and the ARC solenoids block the flow of air.The service brake valve allows air to flow to two double check valves thatblock the passages to the manual retarder and ARC valves. Air pressurefrom the service brake valve flows through the double check valves to theservice brake relay valve and the front brake oil cooler diverter valve.

The service brake relay valve opens and metered air flows from the largeservice brake air tank to the brake cylinders. The relay valves reduce thetime required to engage and release the brakes. A pair of double checkvalves above the brake cylinders prevent the flow of service brake air tothe ARC relay valve.

• Service/retarder brakeair system

• Relay valves reducebraking time

• Double check valvesseparate systems

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Air from the service brake valve also flows to the brake light switch andthe service/retarder brake switch. Depressing the service brake pedalturns ON the brake lights and changes the transmission shift points andanti-hunt timer.

When the manual retarder lever is moved, air flows through three doublecheck valves that block the passages to the service brake valve and theARC valve. Air pressure from the manual retarder brake valve flowsthrough the double check valves to the service brake relay valve and thefront brake oil cooler diverter valve.

Air from the manual retarder brake valve also flows to the retarder switch,the brake light switch and the service/retarder brake switch. Engaging themanual retarder turns ON the retarder dash lamp, the brake lights, andchanges the transmission shift points and anti-hunt timer.

When the ARC is activated, air flows through two double check valvesthat block the passages to the service brake valve and the manual retarderbrake valve. Air pressure from the ARC valve flows through the doublecheck valves to the front brake oil cooler diverter valve.

When the ARC brake system is ENGAGED, the ARC relay valve opensand metered air flows from the service brake tank, through a pressureprotection valve and the double check valves, to the three brake cylinders.The pressure protection valve prevents a total loss of air pressure in theservice brake air system if the ARC relay valve fails. The protectionvalve opens to send flow to the ARC relay valve at 380 kPa (55 psi) andcloses when the pressure decreases below 310 kPa (45 psi).

Air from the ARC valve also flows to the retarder switch, the brake lightswitch and the service/retarder brake switch. Engaging the ARC turnsON the retarder dash lamp, the brake lights, and changes the transmissionshift points and anti-hunt timer.

• Manual retarderoperation

• ARC operation

- Engages ARC relayvalve

• Service brakesactivate two switches

• Pressure protectionvalve prevents air loss

• ARC activates threeswitches

• Manual retarderactivates threeswitches

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• 789C brake oil coolingsystem:

- Three pump sectionsfor rear brakes

- Two pump sectionsfor front brakes

789C BRAKECOOLING SYSTEM

FRONTBRAKES

TORQUECONVERTERCHARGING

FILTER


PARKING BRAKERELEASE VALVE

DIVERTERVALVE

CONVERTEROUTLETFILTER

PARKINGBRAKEFILTER


REAR BRAKES

OUTLETRELIEF VALVE

INLETRELIEF VALVE

HOIST PUMP

HOISTSCREENS

HOISTVALVE

This schematic shows the flow of oil through the 789C brake coolingsystem. Three pump sections provide oil for rear brake cooling: the twosections of the hoist pump and the fourth section of the torque converterpump. Two pump sections provide oil for front brake cooling: the torqueconverter charging and the brake release sections of the torque converterpump. All the pumps pull oil from the hydraulic tank through suctionscreens.

Oil flows from the hoist pump sections through two screens to the hoistvalve. In the HOLD and FLOAT positions, oil from the pump flowsthrough the hoist valve to the rear brake cooling system.

Oil flows from the fourth section of the torque converter pump, joins withthe oil from the hoist valve, and flows to the rear brake oil coolers.

Oil from all three pump sections combines and flows through the screensand rear brake oil coolers located on the right side of the engine. The rearbrake oil coolers are cooled by the engine jacket water cooling system.From the coolers, oil flows through the brakes and returns to the hydraulictank.

• Rear brake cooling

• Hoist pump flow

• Fourth section of TCpump flow

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The pressure in the rear brake cooling system is controlled by the oilcooler relief valve located in the hoist valve. The relief valve setting is790 kPa (115 psi).

Oil flows from the torque converter charging pump through the torqueconverter charging filter, the torque converter, and the torque converteroutlet screen to the front brake oil cooler diverter valve.

Oil flows from the brake release pump through the brake release filter tothe brake release valve. The brake release valve controls the oil pressureto release the parking brakes, lock up the torque converter and shift thedirectional spool in the hoist valve. These functions require minimal oilflow. Most of the oil from the brake release pump flows through thebrake release valve and joins with the torque converter charging pump oilat the front brake oil cooler diverter valve.

When the service or retarder brakes are ENGAGED, the front brake oilcooler diverter valve allows brake cooling oil to flow through the frontbrake oil cooler to the front brakes. When the brakes are RELEASED,the oil bypasses the cooler and flows directly to the brakes. The frontbrake oil cooler is cooled by the engine aftercooler cooling system. Theaftercooler cooling system does not have temperature regulators(thermostats) in the circuit.

Normally, front brake cooling oil is diverted around the cooler and goesdirectly to the front brakes. Diverting oil around the cooler provideslower temperature aftercooler air during high power demands (whenclimbing a grade with the brakes RELEASED, for example).

The brake cooling system on the 785C truck is slightly different from the789C truck. The 785C truck does not have a fourth section on the torqueconverter pump for rear brake cooling. The parking brake release pumpsends oil to the rear brake cooling system, not to the front brake coolingsystem.

• Front brake cooling

• Converter chargingpump flow

• Oil cooler relief valvefor rear brake cooling

• Brake release pumpflow

• Front cooler used onlywith brakesENGAGED

• 785C brake oil coolingsystem

- Three pump sectionsfor rear brakes

- One pump sectionfor front brakes

- 236 -

• Brake cooling oilpressure tap (arrow)

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Shown is the left rear brake housing on a 789C truck. Brake cooling oilpressure can be tested at the two taps (arrow) located in the brake coolingoil tubes. One tap is located on the brake cooling inlet tube and anothertap is located on the brake cooling outlet tube. The pressure measured atthe brake inlet tube (from the oil coolers) will always be higher than thepressure measured at the brake outlet tube.

With the brake cooling oil temperature between 79 to 93°C (175 to 200°F), the pressure measured at the brake inlet tube should beabove 14 kPa (2 psi) at LOW IDLE and below 172 kPa (25 psi) at HIGHIDLE.

Four brake oil temperature sensors, one for each brake, are located in thebrake oil cooling tubes. The brake oil temperature sensors provide inputsignals to the VIMS, which keeps the operator informed of the brakecooling oil temperature.

The most common cause of high brake cooling oil temperature isoperating a truck in a gear that is too high for the grade and notmaintaining sufficient engine speed. Engine speed should be kept atapproximately 1900 rpm during long downhill hauls.

Also, make sure the pistons in the slack adjuster are not stuck andretaining too much pressure on the brakes (see Slides No. 189 and 190).

• Brake cooling oilpressure

• High brake cooling oiltemperature:

- Gear too high

- Engine speed toolow

- Slack adjusterpistons stuck

194

BRAKE ELECTRONIC CONTROL SYSTEM

The "C" Series trucks use an additional Electronic Control Module (ECM)for controlling both the Automatic Retarder Control (ARC) and theTraction Control System (TCS).

The Automatic Retarder Control (ARC) and the Traction Control System(TCS) control modules are replaced with one Brake ECM. The BrakeECM controls both the ARC and the TCS functions. The TCS is now onthe CAT Data Link, and the Electronic Technician (ET) service tool canbe used to diagnose the TCS.

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PROPORTIONAL(SERVO) SOLENOID

TCSENGAGED LAMP TCS SELECTOR SOLENOID

LEFT AND RIGHT

ARC SUPPLYSOLENOID

RIGHT WHEEL SPEED SENSOR

INPUT COMPONENTS

OUTPUT COMPONENTS

ENGINE OUTPUTSPEED SENSOR


ENGINE ECM

SERVICE TOOLCAT DATA LINK

ARC CONTROLSOLENOID

LEFT WHEEL SPEED SENSOR

ARC ON/OFFSWITCH

ON INPUT

OFF INPUT

RETARDERENGAGED LAMPAUTO RETARDER

PRESSURE SWITCH

RETARDERPRESSURE SWITCH

TCS TESTSWITCH

ARC

TCS

ARC

TCS

SHIFT LEVERSWITCH

ACTUAL GEARSWITCH

PARKING/SECONDARYBRAKE SWITCH

TRANSMISSION OUTPUTSPEED SENSOR

SERVICE/RETARDERBRAKE SWITCH

THROTTLESENSOR

ENGINESPEED/TIMING

SENSOR

BRAKE ELECTRONIC CONTROL SYSTEM

VIMS

BRAKE OVERSTROKESWITCH

DIFFERENTIALOIL LEVEL

DIFFERENTIALFILTER

PARKING BRAKE FILTER

DIFFERENTIAL FAN RELAY

LEFT BRAKERELEASE

PRESSURERIGHT BRAKE

RELEASE PRESSURE

DIFFERENTIAL OILTEMP SENSOR

BRAKE AIR PRESSURE

DIFFERENTIALPRESSURE

• Brake ECM

The Brake ECM receives information from various input componentssuch as the Engine Output Speed (EOS) sensor, retarder pressure switch,left and right wheel speed sensors and the TCS test switch.

Based on the input information, the Brake ECM determines whether theservice/retarder brakes should ENGAGE for the ARC or theparking/secondary brakes should ENGAGE for the TCS. These actionsare accomplished by sending signals to various output components.

Output components include the ARC supply and control solenoids, theretarder ENGAGED lamp, the TCS selector and proportional solenoidsand the TCS ENGAGED lamp.

The Brake ECM also provides the service technician with enhanceddiagnostic capabilities through the use of onboard memory, which storespossible diagnostic codes for retrieval at the time of service.

The Engine ECM, the Transmission/Chassis ECM, the Vital InformationManagement System (VIMS) and the Brake ECM all communicatethrough the CAT Data Link. Communication between the electroniccontrols allows the sensors of each system to be shared.

The Electronic Control Analyzer Programmer (ECAP) and the ElectronicTechnician (ET) Service Tools can be used to perform several diagnosticand programming functions.

Some of the diagnostic and programming functions that the service toolscan perform are:

- Display real time status of input and output parameters

- Display the internal clock hour reading

- Display the number of occurrences and the hour reading of the firstand last occurrence for each logged diagnostic code and event

- Display the definition for each logged diagnostic code and event

- Display the supply and control solenoid engagement counter

- Program the ARC control speed

- Perform ARC diagnostic tests

- Upload new Flash files

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• Brake functionscontrolled byelectrical signals

• Benefits of electroniccommunication

• Service tool functions

195

The Brake ECM (arrow) is located in the compartment at the rear of thecab. The Brake ECM does not have a diagnostic window like the ARCand the TCS used on the "B" Series trucks.

All diagnostic and programming functions must be performed with anElectronic Control Analyzer Programmer (ECAP) or a laptop computerwith the Electronic Technician (ET) software installed. ET is the tool ofchoice because the Brake ECM can be reprogrammed with a "flash" fileusing the WinFlash application of ET. ECAP cannot upload "flash" files.

The Brake ECM looks like the Engine ECM with two 40-pin connectors,but the Brake ECM does not have fittings for cooling fluid. Also, theBrake ECM has no access plate for a personality module.

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• Brake ECM (arrow):

- No diagnosticwindow

- Diagnostics andprogrammingrequire ECAP or ET

• Brake ECM looks likeEngine ECM

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AUTOMATICRETARDER

VALVE

SUPPLYSOLENOID

CONTROLSOLENOID

AUTO RETARDERPRESSURE SWITCH

VENT

RETARDERENGAGED

LAMP

CAT DATA LINK

ARC ON/OFFSWITCH

ON INPUT

OFF INPUT

AIR FROMSERVICE BRAKE

RESERVOIR

SERVICEBRAKEVALVE

MANUALRETARDER

VALVE

RETARDERPRESSURE

SWITCH

TO SERVICE /RETARDER BRAKE

RELAY VALVE

VENT

ENGINE SPEEDSENSOR

TO ARCRELAY VALVE

BRAKE ECM(ARC/TCS)


ENGINE ECMSERVICE TOOL

VIMS

AUTOMATIC RETARDER CONTROL

Automatic Retarder Control (ARC)

The Automatic Retarder Control (ARC) system function is to modulatetruck braking (retarding) when descending a long grade to maintain aconstant engine speed. The ARC system engages the service/retarderbrakes. If the ON/OFF switch is moved to the ON position, the ARC willbe activated if the throttle pedal is not depressed and the parking/secondary brakes are RELEASED. The ARC system is disabled when thethrottle is depressed or when the parking/secondary brakes areENGAGED.

The ARC is not connected to the service brakes and the manual retarder.When the ARC is ENGAGED, air flows from the ARC valve to a separaterelay valve located near the brake master cylinders (see Slide No. 182).

• Automatic RetarderControl (ARC)

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The ARC is set at the factory to maintain a constant engine speed of 1900 ± 50 rpm (engine speed setting is programmable). When the ARCinitially takes control of retarding, the engine speed may oscillate out ofthe ± 50 rpm target, but the engine speed should stabilize within a fewseconds.

For proper operation of the ARC, the operator needs only to activate thecontrol with the ARC ON/OFF switch and select the correct gear for thegrade, load, and ground conditions. The ARC is designed to allow thetransmission to upshift to the gear selected by the shift lever. After thetransmission shifts to the gear selected by the operator and the enginespeed exceeds 1900 rpm, the ARC will apply the retarder as needed tomaintain a constant engine speed.

The ARC system also provides engine overspeed protection. If an unsafeengine speed is reached, the ARC will engage the brakes, even if the ARCON/OFF switch is in the OFF position and the throttle is depressed.

Trucks approaching an overspeed condition will sound a horn and activatea light at 2100 rpm. If the operator ignores the light and horn, the ARCwill engage the retarder at 2180 rpm. If the engine speed continues toincrease, the Transmission/Chassis ECM will either upshift (one gear onlyabove shift lever position) or unlock the torque converter (if the shift leveris in the top gear position) at 2300 rpm.

The ARC also provides service personnel with enhanced diagnosticcapabilities through the use of onboard memory, which stores possiblefaults, solenoid cycle counts and other service information for retrieval atthe time of service.

By using an ECAP or a laptop computer with the Electronic Technician(ET) software installed, service personnel can access the stored diagnosticinformation or set the adjustable engine speed control setting.

The Auto Retarder Control receives signals from several switches andsensors. The control analyzes the various input signals and sends signalsto the output components. The output components are two solenoids anda lamp.

INSTRUCTOR NOTE: For more detailed information about theAutomatic Retarder Control (ARC) system, refer to the ServiceManual Module "Automatic Retarder Control System" (FormSENR5683) and the Technical Instruction Module "AutomaticRetarder Control System" (Form SEGV2593).

• ARC providesprogramming anddiagnostic capability

• ARC provides engineoverspeed protection

• ARC set to maintain1900 engine rpm

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STMG 70611/98

2

1

Shown is the location of the Engine Output Speed (EOS) sensor (1) thatprovides the primary input signal used by the ARC. The engine speedinformation is the main parameter that the Brake ECM uses to controlretarding. The engine speed sensor is a frequency sensor that generatesan AC signal from the passing flywheel gear teeth.

The engine speed/timing sensor (2) is also used by the ARC for diagnosticpurposes. If the Brake ECM receives an input signal from the enginespeed/timing sensor, but not the EOS sensor, the Brake ECM will log anengine speed fault. The ARC will not function without an engine speedsignal from EOS sensor (1).

NOTE: The 8T5200 Signal Generator/Counter Group can beconnected to the engine speed sensor wiring harness and be used tosimulate engine speed for diagnostic purposes. To connect the8T5201 Signal Generator to the engine speed sensor wiring harness,fabricate jumper wires and connect the 8T5198 Adapter Cable (partof the 8T5200 Signal Generator/Counter Group) to the speed sensorharness Deutsch DT connector.

8T5198 Adapter Deutsch DT Connector

Pin B J765 BU Pin 2 (ground)Pin C 450 YL Pin 1 (signal)

1. Engine output speedsensor

2. Engine speed/timingsensor

• Use 8T5200 SignalGenerator to simulateengine speed

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1. Retarder pressureswitch

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STMG 70611/98

1

5

4

3

2

Shown is the location of the retarder pressure switch (1). The retarderpressure switch signals the Brake ECM when manual or automaticretarder air pressure is present. The switch is normally open and closeswhen the manual or automatic retarder is engaged.

A fault is recorded when the Brake ECM detects the absence of retarderpressure (switch open) while the supply solenoid and the control solenoidare energized.

The auto retarder pressure switch (2) signals the Brake ECM when airpressure is present and the automatic retarder valve (3) is functioning.The auto retarder pressure switch is located in front of the cab in theoutput port of the automatic retarder valve. The switch is normally closedand opens only when the auto retarder is engaged.

A fault is recorded when the Brake ECM detects the presence of autoretarder pressure (switch open) while the supply solenoid and the controlsolenoid are not energized.

2. Auto retarderpressure switch

3. Automatic retardervalve

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The supply solenoid valve (4) turns ON or OFF to control the flow ofsupply air to the automatic retarder valve (3). The Brake ECM energizesthe supply solenoid valve with +Battery voltage (24 Volts) at 100 rpm lessthan the programmed control speed setting. Normally, the reduced speedwill be 1800 rpm, since the control speed is set to 1900 rpm at the factory.

A fault is recorded if the Brake ECM senses the signal to the supplysolenoid as open, shorted to ground, or shorted to battery.

The control solenoid valve (5) modulates the air flow to the brakes duringautomatic retarding. The control solenoid receives a Pulse WidthModulated (PWM) signal from the Brake ECM. The longer the dutycycle, the more time the control solenoid valve is open, and more airpressure is allowed to the brakes. Voltage to the control solenoidincreases proportionally from zero to approximately 22 Volts with thedemand for more brake pressure.

A fault is recorded if the Brake ECM senses the signal to the controlsolenoid as open, shorted to ground, or shorted to battery.

Normal resistance through the supply and control solenoids is 31 Ohms.An excess resistance of approximately 40 Ohms will prevent the valvesfrom opening and will cause a supply or control valve fault to be logged.Therefore, a measurement of approximately 71 Ohms or more will showthat the solenoid is defective.

The Brake ECM can also determine if the solenoid valves havemalfunctioned (valves leaking). If air pressure is present at the autoretarder pressure switch when the solenoids are DE-ENERGIZED, theauto retarder pressure switch will signal the Brake ECM that the ARCvalve has malfunctioned.

5. Control solenoidvalve

• Supply and controlsolenoid resistance

• ARC valvemalfunction

4. Supply solenoidvalve

199

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BRAKE ECM(ARC/TCS)

TRACTION CONTROL SYSTEM

PROPORTIONALSOLENOID

TCSENGAGED

LAMP

TCS SELECTORSOLENOID

LEFT AND RIGHT

RIGHT WHEELSPEED SENSOR

LEFT WHEELSPEED SENSOR

TCS TESTSWITCH

ELECTRONICSERVICE TOOL

CAT DATA LINK


TRANSMISSIONOUTPUT SPEED

SENSOR

+ 10V TOWHEEL SENSORS

Traction Control System (TCS)

The Traction Control System (TCS) uses the rear parking/secondarybrakes (spring engaged and hydraulically released) to decrease therevolutions of a spinning wheel. The TCS allows the tire with betterunderfoot conditions to receive an increased amount of torque. Thesystem is controlled by the Brake ECM (see Slides No. 194 and 195).

The Brake ECM monitors the drive wheels through three input signals:one at each drive axle, and one at the transmission output shaft. When aspinning drive wheel is detected, the Brake ECM sends a signal to theselector and proportional valves which ENGAGE the brake of the affectedwheel. When the condition has improved and the ratio between the rightand left axles returns to 1:1, the Brake ECM sends a signal to RELEASEthe brake.

• TCS uses rearparking/secondarybrakes

- 246 -STMG 70611/98

The TCS was formerly referred to as the Automatic Electronic TractionAid (AETA). The operation of the system has not changed. The maindifferences are the appearance of the ECM, and the TCS is now on theCAT Data Link. Also, the ECAP and ET Service Tools can communicatewith the TCS.

A service/retarder brake switch (see Slide No. 128) provides an inputsignal to the TCS through the CAT Data Link and performs two functions:

1. When the service brakes or retarder are ENGAGED, the TCS functionis stopped.

2. The service/retarder brake switch provides the input signal needed toperform a diagnostic test. When the TCS test switch and the retarderlever are ENGAGED simultaneously, the TCS will engage each rearbrake independently. Install two pressure gauges on the TCS valve,and observe the pressure readings during the test cycle. The left brakepressure will decrease and increase. After a short pause, the rightbrake pressure will decrease and increase. The test will repeat as longas the TCS test switch and the retarder lever are ENGAGED.

The TCS valve has a left and right brake release pressure sensor. Alaptop computer with the ET software installed can also be used to viewthe left and right parking brake pressures during the test discussed abovein function No. 2. When the proportional solenoid is ENERGIZED, ETwill show 44% when the brake is FULLY ENGAGED.

NOTE: During the diagnostic test, the parking/secondary brakesmust be released.

• Service/retarder brakeswitch:

- Stops TCS function

- Performs diagnostictest

• TCS replaces AETA

• Brake releasepressure sensors

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STMG 70611/98

Shown is the right rear wheel speed sensor (arrow). The TCS monitorsthe drive wheels through three input speed signals: one at each drive axle,and one at the transmission output shaft.

The Transmission Output Speed (TOS) sensor (see Slide No. 127)monitors the ground speed of the machine and provides input signals tothe TCS through the CAT Data Link. The TCS uses the TOS sensor todisable the TCS when ground speed is above 19.3 km/h (12 mph).

• Wheel speed sensor(arrow)

• TOS sensor disablesTCS

- 248 -

• TCS valve

201

STMG 70611/98

4

2

3

1

3

4

The Traction Control System (TCS) valve is mounted inside the rear ofthe left frame rail. Two solenoids are mounted on the valve.

Electrical signals from the Brake ECM cause the selector solenoid valve (1) to shift and select either the left or right parking brake. If theselector valve shifts to the left parking brake hydraulic circuit, the controloil is drained. The left reducing spool of the control valve can then shiftand engage the parking brake.

The Brake ECM energizes the selector solenoid valve with + Batteryvoltage (24 Volts). Normal resistance through the selector solenoid isbetween 18 and 45 Ohms.

The proportional solenoid valve (2) controls the volume of oil beingdrained from the selected parking brake control circuit. The rate of flowis controlled by a signal from the Brake ECM.

The proportional solenoid receives a Pulse Width Modulated (PWM)signal from the Brake ECM. The longer the duty cycle, the more time theproportional solenoid valve is open, and more oil pressure is drained fromthe brakes. Voltage to the proportional solenoid increases proportionallyfrom zero to approximately 10 Volts with the demand for more braking.Normal resistance through the solenoid is between 12 and 22 Ohms.

The pressure taps (3) or pressure sensors (4) can be used to check the leftand right brake release pressures when performing diagnostic tests on theTCS. The pressure at the taps in the TCS valve will be slightly less thanthe brake release pressure measured at the wheels.

1. Selector solenoid

2. Proportional solenoid

3. Left and right brakerelease pressure taps

4. Left and right brakerelease pressuresensors

202

- 249 -STMG 70611/98

• TCS operation withbrakes RELEASED

PARKINGBRAKEVALVE

TRANSMISSIONSPEED SENSOR


SELECTORSOLENOID


SCREEN

ORIFICE

LEFTDRIVE AXLE

RIGHTDRIVE AXLE

TRACTION CONTROL SYSTEM (TCS)ENGINE RUNNING/BRAKES RELEASED

BALL CHECK

OUTPUTSIGNALS

INPUTSIGNALS

TCS ENGAGEDLAMP

TESTSWITCH

Shown is the TCS with the engine running and the brakes RELEASED.

When the machine is started:

- Oil flows from parking brake release pump through the brake releaseoil filter where the flow is divided. One line from the filter directsoil to the parking brake release valve. The other line sends oil to thesignal port (right end of signal piston) of the TCS control valve.

- Oil flow to the TCS control valve signal port causes the ball checkpiston to move to the left and unseat the drain ball check valve.Opening the drain ball check valve opens a drain passage to thehydraulic tank.

- 250 -STMG 70611/98

When the operator releases the parking brakes:

- Air pressure is increased at the parking brake release valve forcingthe valve spool down.

- Parking brake release oil can now flow through the parking brakerelease valve to the TCS control valve.

- In the control valve, oil closes the parking/secondary ball checkvalve and flows through the screen.

- Oil flows through the right and left brake control circuit orifices.

- Oil flows to the ends of the left and right brake reducing valvespools.

- When the control circuit pressure is high enough, the reducingspools shift toward the center of the TCS control valve and parkingbrake release oil flows to release the brakes.

203

- 251 -STMG 70611/98

• CS operation with leftbrake ENGAGED

PARKINGBRAKEVALVE

TESTSWITCH

SELECTORSOLENOID


SCREEN

ORIFICE

LEFTDRIVE AXLE

RIGHTDRIVE AXLE

TRACTION CONTROL SYSTEM (TCS)ENGINE RUNNING/LEFT BRAKE ENGAGED

BALL CHECK

OUTPUTSIGNALS

INPUTSIGNALS

TRANSMISSIONSPEED SENSOR


TCS ENGAGEDLAMP

Shown is the TCS with the engine running and the left brake ENGAGED.When signals from the sensors indicate that the left wheel is spinning 60% faster than the right wheel, the following sequence of events occurs:

- The Brake ECM sends a signal to the selector solenoid valve and theproportional solenoid valve.

- The selector solenoid valve opens a passage between the outer endof the left brake pressure reducing valve and the proportionalsolenoid valve.

- The proportional solenoid valve opens a passage from the selectorsolenoid valve to drain. The proportional solenoid valve alsocontrols the rate at which the oil is allowed to drain.

- Control circuit oil drains through the selector valve and enters theproportional valve.

- 252 -STMG 70611/98

- The reducing valve spool for the left parking brake shifts and blocksthe flow of oil to the parking brake.

- Oil in the left parking brake control circuit begins to drain.

- The left parking brake begins to ENGAGE.

- The left brake orifice restricts the flow of oil from the parking brakerelease valve.

When the signals from the sensors indicate that the left wheel is no longerspinning, the following sequence occurs:

- The Brake ECM stops sending signals to the selector solenoid andthe proportional solenoid.

- The selector solenoid valve and proportional solenoid valve blockthe passage to drain and allow the control circuit pressure toincrease.

- The left brake reducing valve spool shifts to the center position andblocks the passage to drain.

- Parking brake release oil is directed to the left parking brake and thebrake is RELEASED.

INSTRUCTOR NOTE: For more detailed information on theTraction Control System (TCS) refer to the Service Manual module"Automatic Electronic Traction Aid" (Form SENR2986) and theTechnical Instruction Module "Automatic Electronic Traction Aid"(Form SEGV2585).

- 253 -

204

STMG 70611/98

1

3

2

OPTIONAL EQUIPMENT

FlexxaireTM Fan

Shown is a 3516B Engine with a FlexxaireTM Fan installed. TheFlexxaireTM fan provides full control of air movement through the radiatorwith an automatically controlled, variable pitch fan. The fan is designedto help control cooling requirements in specific applications such as coldweather and high altitude. The thermostatic controller automaticallyadjusts the blade pitch to maintain an optimum engine coolanttemperature.

With zero-pitch start-up, the air dam effect prevents air flow through theradiator and the engine reaches the recommended operating temperaturemore quickly. The pitch will vary throughout the day based on the enginecooling temperature and air conditioning requirements. The automaticblade pitch control reduces the horsepower loss when engine cooling isnot required.

The 10 fan blades attach to the hub assembly (1). A coolant temperaturesensor (2) and an air conditioning pressure sensor (see Slide No. 62)provide input signals to an electronic control box located behind the cab(see next page). The electronic control analyzes the input signals andsends an electrical signal to the actuator (3). The actuator rotates andchanges the fan pitch as needed to increase or decrease the engine coolanttemperature.

• Flexxaire fan:- Variable pitch - Temperature

controlled

• Warms engine quickly

• Reduces horsepowerloss

1. Hub assembly

2. Coolant temperaturesensor

3. Fan pitch actuator

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2

3

1

4

The FlexxaireTM Fan electronic control box (1) and the remote display (2)are located in the compartment behind the operator's station. The controlbox is used to set up and calibrate the Flexxaire fan. Remove the coverfrom the control box and follow the instructions on the label inside thecover.

The FlexxaireTM control box provides many features. The customer mustdecide which features he wants to use before setting up the system. Someof the features are:

Timed Auto-Purge, Purge Interval Override, TemperatureDriven Auto-Purge: Off-highway Trucks normally PULL airthrough the radiator. For a PURGE to occur, the fan blades rotateand PUSH air through the radiator. Changing air flow directioncan help clear debris from the radiator.

Actuator Stall Detection: If the fan pitch actuator encountersexcessive resistance (bolt falls into the linkage), the control willsense the increased current and attempt an automatic calibration.If the obstruction continues, as a safety measure, the control willrotate the fan blades to full pitch.

1. Electronic controlbox

2. Remote display

• Control features

- 255 -STMG 70611/98

Second Fluid Temperature Control: A second temperaturesensor can be installed to control the fan pitch in addition to theengine coolant temperature sensor (brake oil temperature).

Blaze Blocker: A fire suppression system can provide an inputsignal to the control that will rotate the fan blades to theNEUTRAL position. In the NEUTRAL position, the fan providesno air flow. Limiting the air flow reduces the amount of oxygen tothe fire, and the fire suppressant is not blown from the enginecompartment.

The following two FlexxaireTM Fan Controls must be set up properly:

Actuator Limits: This procedure sets the travel limits and theNEUTRAL position of the actuator.

Temperature Set Point Calibration: This procedure sets thetemperature range that the controller will try to maintain bychanging the fan pitch.

The remote display (2) can be used to change the air flow from PUSH toPULL by depressing the air flow button (3). The nine LED bar display tothe right of the air flow button indicates the position of the fan. Thebottom four LED's indicate the PULL direction. The center LEDindicates the NEUTRAL position. The top four LED's indicate the PUSHdirection.

The purge button (4) will start the purge cycle if one has beenprogrammed into the control (optional).

INSTRUCTOR NOTE: More detailed information about theFlexxaireTM Fan System can be found in the Service Manual module"FlexxaireTM Fan Installation And Maintenance Manual" (Form SEBC1152).

• Fan setuprequirements:

- Actuator limits

- Temperature setpoints

2. Remote display

3. Air flow button

- LED bar display

4. Purge button

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CONCLUSION

This presentation has provided a basic introduction to the Caterpillar785C and 789C Off-highway Trucks. All the major component locationswere identified and the major systems were discussed. When used inconjunction with the service manual, the information in this packageshould permit the serviceman to analyze problems in any of the majorsystems on these trucks.

1. 789C model view2. Right side 789C truck3. Front of 789C truck4. Truck body options5. Walk around inspection6. Maintenance checks7. Front wheel bearing8. Front suspension cylinder9. Air filter housing

10. Right side engine11. Transmission charging filter12. Transmission hydraulic tank13. Final drive14. Differential oil level15. Safety cable16. Fuel tank17. Primary fuel filter18. Parking brake and torque converter19. Brake cylinder breathers20. Front air dryer21. 789C engine oil filters22. 785C engine oil filters23. Oil change connector24. Secondary fuel filters25. Engine shutdown switch26. Air filter restriction indicators27. 789C cooling system28. Air cleaner indicators29. Ether cylinders30. Batteries31. Lubrication tank32. Steering system tank33. Air tank drain valve34. Windshield washer reservoir35. Daily checks36. Operator's station37. Operator and trainer seats38. Hoist control lever39. Dash (left side)40. Operator controls 41. Switches and signals42. Manual retarder lever43. Brake and throttle pedals44. Shift console45. Overhead switches

46/ Circuit breaker panel47. Center dash panel48. Rocker switches49. VIMS message center module50. VIMS interface modules51. VIMS main module52. VIMS diagnostic connector53. Electronic Technician (ET)54. 3516B engine model view55. Electronic control system component

diagram56 Engine ECM57. Atmospheric pressure sensor58. Engine speed/timing sensor59. Throttle position sensor60. EUI fuel injector solenoid61. Input switches and sensors62. Air conditioner compressor switch63. Crankcase pressure sensor64. ECM logged events65. Additional ECM logged events66. Systems controlled by ECM67. Engine oil pre-lubrication68. Speed fan control69. Oil renewal system components70. Oil level switches71. Cooling system72. Radiator73. Water pump74. Coolant 75. Engine (right side)76. Jacket water coolant flow77. Auxiliary (aftercooler) water pump78 Rear aftercooler temperature sensor79. 789C air charging system80. Lubrication system81. Oil filters82. 785C engine oil filters83. Engine oil system84. Primary fuel filter85. Fuel transfer pump86. Secondary fuel filters87. Fuel injectors88. Fuel system circuit89. Air induction and exhaust system

SLIDE LIST

STMG 706 - 257 -11/98

90. Turbocharger inlet pressure sensor91. 351B turbochargers92. Exhaust temperature sensor93. 3512B air induction and exhaust system94. Power train components95. Torque converter96. Torque converter (converter drive)97. Torque converter drive (direct drive)98. Torque converter pump (four sections)99. Torque converter charging filter100. Torque converter inlet relief valve101. Torque converter outlet screen102. Brake oil cooler and diverter valve103. Parking brake release valve104. Torque converter lockup clutch valve (iron)105. Torque converter lockup clutch control

(direct drive)106. Torque converter hydraulic system107. Transfer gears108. Transmission lube supply hose109. Power shift planetary transmission110. Transmission pump111. Transmission scavenge screens112. Transmission charging filter113. Transmission oil cooler bypass valve and oil

cooler114. Transmission charging pump115. Transmission clutch pressures116. ICM transmission controls (sectional view)117. Transmission hydraulic system118. Rear axle pump119. Pump supply hose120. Oil filter bypass switch121. Rear axle oil cooling and filter system122. Double reduction planetary gear final drives123. Transmission/Chassis ECM124. Transmission/Chassis electronic control

system125. Shift lever switch126. Transmission gear switch127. Transmission Output Speed (TOS) sensor128. Service/retarder brake switch129. Body position sensor130. Steering system

131. 789C steering system (no steer/maximumflow

132 785C steering system (hold)133. Steering tank and filter134. 785C steering pump135. 785C steering pump (maximum flow)136. Pump compensator valve137. 785C steering pump (minimum flow)138. 789C steering pump 139. 789C steering pump supply oil 140. 789C steering pump operation (maximum

flow)141. 789C steering pump (low pressure standby)142. Accumulator charging valve143. Load sensing controller144. 789C solenoid and relief valve manifold145. 785C solenoid and relief valve manifold146. Solenoid and relief valve manifold

(sectional view)147. 789C steering directional valve148. Steering directional valve (no turn)149. Steering directional valve (right turn)150. 785C solenoid and relief valve manifold and

crossover relief valves151. 785C crossover relief system (external

impact)152. 789C Hand Metering Unit (HMU)153. 789C steering accumulators154. Shutdown control155. Hoist control system156. Hoist lever157. Hoist control position sensor158. Hoist, converter and brake tank159. Hydraulic tanks (rear)160. Two section hoist pump161. Hoist screens162. Pump supply ports163. Counterbalance valve164. Hoist control valve (hold)165. Hoist control valve (raise)166. Hoist counterbalance valve (raise, lower and

float)167. "C" Series hoist control valve (lower)168. "C" Series hoist control valve (float)

SLIDE LIST

STMG 601 - 258 -5/91

169. Two-stage hoist cylinders170. Hoist system (hold)171. Air and brake systems172. Oil cooled brake assembly (cutaway)173. Air charging system174. 789C air dryers175. Service/retarder brake tank176. Pressure protection valve177. Automatic lubrication solenoid air valve178. Parking/secondary brake tank179. 789C air charging system180. Manual retarder valve181. Service brake valve182. Inverter valve signal port183. Brake release valve184. Normal parking and secondary brake

operation185. Parking/secondary brakes released and

parking brakes engaged186. Service brake and manual retarder relay

valve187. Brake oil makeup tank188. Brake cylinder (engaged)189. Slack adjuster (iron)190. Slack adjuster (released and engaged)191. Service/retarder brake air system (engaged)192. 789C brake oil cooling schematic193. Brake cooling oil pressure tap194. Brake electronic control system 195. Brake ECM (iron)196. Automatic Retarder Control (ARC)

schematic197. Engine Output Speed (EOS) sensor198. Retarder pressure switch199. Traction Control System (TCS) schematic200. Wheel speed sensor201. Traction Control System (TCS) valve202. Traction Control System (TCS) operation

(brakes released)203. Traction Control System (TCS) operation

(left brake engaged)204. Flexxaire fan205. Flexxaire fan electronic control box206. Model rear view

SLIDE LIST

STMG 601 - 259 -5/91

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Serviceman's Handout No. 1

"C" SERIES TRUCK SERVICE TOOLS

MAINTENANCE

2P8250 Filter Strap Wrench4C5084 Filter Cutting Tool4C9301 Coolant Conditioner Test Kit4C4911 Battery Load Tester1U9921 Battery Post Cleaner5P0957 Coolant and Battery Tester (°F)5P3514 Coolant and Battery Tester (°C)9U5617 Suspension oil fill unit7S5437 Nitrogen Charging Group5P8610 Nitrogen Charging Adapter (for charging two suspension cylinders)1U5551 Valve Extension (for charging steering accumulators)7S9394 Tire Fill Air Hose 7F8240 Tire Valve Repair Tool1P0545 Tire Gauge6V4040 Nitrogen Tire Inflation Kit5P1720 Seal Pick

ENGINE

9U7400 Multitach II Group9S9082 Engine Turning Tool1U5470 Engine Pressure Gauge Group1U5440 Fuel Flow Monitor Group (3400/3500)147-5482 3500/3500B Valve Lash Setting Group147-2056 Dial Indicator (inches) (need with 147-5482)147-5537 Dial Indicator (metric) (need with 147-5482)148-7211 Bridge Nut Socket (need with 147-5482)9U5132 Injector Height Tool Group

ELECTRONIC CONTROL DIAGNOSTICS

Laptop Computer for VIMS and ETIBM Compatible Computer with DB-9 or DB-25 Pin RS-232 Serial Port

Vital Information Management System (VIMS)JERD2093 Caterpillar Common Services SoftwareJERD2137 VIMS Software LicenseJERD2138 VIMS Software SubscriptionJERD2139 VIMS Software Subscription (additional copies)127-9797 VIMS Computer to Truck Adapter Cable (same as TPMS)

- 261 -STMG 70611/98


ELECTRONIC CONTROL DIAGNOSTICS (continued)

Electronic Technician (ET)JEBD3003 ET Getting Started Book and CDJERD2124 Electronic Technician (ET) Software LicenseJERD2129 ET Software Subscription (Engines and Machines)JERD2142 ET Software Subscription (Machines Only)7X1700 Communication AdapterNEXG4523 Service Program Module (SPM) for Communication Adapter139-4166 ET Universal Cable (connects Communication Adapter to machine;

for CAT Data Link and ATA Communication)7X1425 ET Adapter Cable (connects Laptop to Communication Adapter)7X1695 Timing Probe Cable (for timing calibration)6V2197 Timing Probe Magnetic Pickup (for timing calibration)6V3093 Timing Probe Adapter Sleeve (for timing calibration)LERQ3133 HyperACCESS/5--Flash File Download Software

ELECTRICAL

4C3406 Deutsch Connector Kit (HD10 with crimp tool)9U7246 Deutsch Connector Kit (DT no crimp tool)1U5804 Deutsch Connector Crimp Tool (part of 4C3406)6V3000 Sure Seal Repair Kit1P2305 Terminal and Connector Repair Kit8T0900 AC/DC Clamp-on Ammeter146-4080 Digital Multimeter (reads PWM and Frequency)9U7330 Fluke 87 Digital Multimeter (reads PWM and Frequency)8T3224 Multimeter Probes (for checking CE connectors)7X1710 Signal Reading Probe Group (spade slides in connectors)4C9024 Service Tool and Soldering Iron Battery9U7560 Field Soldering Iron Group (used with 4C9024)5P4205 5/32 T-handle Allen wrench for DRC connectors121-9587 Deutsch Connector (HD10/DRC)--Blue removal tool4C4074 CE Connector--Black removal tool

- 262 -STMG 70611/98


POWER TRAIN

8T5200 Signal Generator (substitutes transmission/engine speed signals)6V4157 Transmission/Hydraulic System Pressure Gauge Group6V6064 Test Cover (top of ICM transmission)

TEMPERATURE MEASUREMENTS

4C6500 Digital Thermometer Group8T2844 Temperature Recorder Stickers4C6090 Multichannel Temperature Selector Group6V9130 Temperature Adapter Group (for Digital Multimeter)8T5334 Surface Temperature Probe123-6700 Infrared Thermometer with Laser Sight148-2400 Compact Infrared Thermometer with Laser sight

MISCELLANEOUS

FT1114 7H1447 Vacuum Cap Assembly--7H1447 Hydraulic CapFT1115 4J3754 Vacuum Cap Assembly--4J3754 Hydraulic Cap5P0306 Transducer6V4142 Open nipple 1/8-27 NPTF5K5068 Pipe Nipple 1/8-27 x 1/8-27 NPTF male union3B6488 Black Pipe Coupling 1/4-18 NPTF both ends5P1750 to 5P1756 Thin plates slide in hose ends to block oil5P1750 Blocker Plate 1.25 in ID Line5P1756 Blocker Plate 4.00 in ID Line6V7830 Tetragauge1U5481 Pressure Gauge Group1U5482 Pressure Adapter Group for 1U54814C4892 ORFS Fitting and Gauge Group8T5320 Hydraulic Test Group (contains blocker plates)5P1404 Adapter (7/8-14 male x 9/16-18 female) for brake bleed port2P8421 Adapter (1 1/16-12 male x 9/16-18 female) for brake cooling pressure

at hoist valve1U5000 Auxiliary Power Unit (gas engine powered pump for dumping or towing)1U5525 Auxiliary Power Unit Attachment Group146-1738 Precision Borescope1U8869 Digital Dial Indicator6V6042 Dial Indicator Contact Group8T5096 Magnetic Dial Indicator Group8T1000 Digital Positioner GroupFT1975 Suspension Gauge Block

Stop Watch

- 263 -STMG 70611/98

785C/789C TRANSMISSION/CHASSIS ECM PIN IDENTIFICATION

Pin Number Chassis Control Function Type Of Pin

J1- 1 Battery+ (24V) PowerJ1- 2 Battery- (ground) PowerJ1- 3 CAT Data Link- CAT Data Link-J1- 4 Dash Body Up Lamp Proportional Driver No. 2J1- 5 Battery- (ground) PowerJ1- 6 Battery+ (24V) PowerJ1- 7 Solenoid Return Solenoid ReturnJ1- 8 Start Relay ON/OFF Driver No. 13*J1- 9 CAT Data Link+ CAT Data Link+J1-10 Secondary Steering Relay Proportional Driver No. 1J1-11 Lockup Clutch Solenoid Proportional Driver No. 4J1-12 Upshift Solenoid Proportional Driver No. 11J1-13 Transmission Charge Filter Switch Switch To Ground 8J1-14 Shift Lever 1 Switch To Ground 16J1-15 Switch and Sensor Ground Return Switch and Sensor GroundJ1-16 Switch and Sensor Ground Return Switch and Sensor GroundJ1-17 Unused Proportional Driver No. 3J1-18 Downshift Solenoid Proportional Driver No. 12J1-19 Shift Lever 4 Switch To Ground 7J1-20 Transmission Lube Filter Switch Switch To Ground 3J1-21 Location code 1 (open) Switch To Ground 26J1-22 Location code 0 (grounded) Switch To Ground 25J1-23 Shift Lever Ground Verify Switch To Ground 6J1-24 Shift Lever 2 Switch To Ground 2J1-25 Service Brake Pressure Switch Switch To Ground 12J1-26 Secondary Brake Pressure Switch Switch To Ground 13J1-27 Shift Lever 5 Switch To Ground 28J1-28 ECM Location Enable (+Battery) Switch To Battery 3J1-29 Transmission Gear 1 Switch To Ground 4J1-30 Transmission Gear 2 Switch To Ground 1J1-31 Transmission Gear 3 Switch To Ground 10J1-32 Transmission Gear 4 Switch To Ground 14J1-33 Transmission Gear 5 Switch To Ground 29J1-34 Unused Switch To Battery 2J1-35 Shift Lever 3 Switch To Ground 5J1-36 Transmission Gear Ground Verify Switch To Ground 15J1-37 Low Steering Pressure Switch Switch To Ground 11J1-38 Location Code 2 (open) Switch To Ground 27J1-39 Hoist Screen Switch Switch To Ground 9J1-40 Key Switch Input Switch To Battery 1*

* The J1-8 driver receives power from the J1-40 input.


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785C/789C TRANSMISSION/CHASSIS ECM PIN IDENTIFICATION


J2- 1 Hoist Enable Relay Proportional Driver No. 6J2- 2 Unused Proportional Driver No. 8J2- 3 Solenoid Return Solenoid ReturnJ2- 4 Transmission Oil Temperature Sensor PWM 4/Switch To Gnd 33J2- 5 Unused PWM 2/Switch To Gnd 31J2- 6 T/C Oil Temperature Sensor PWM 6/Switch To Gnd 35J2- 7 Float Solenoid Proportional Driver No. 5J2- 8 Autolube Solenoid Proportional Driver No. 7J2- 9 Unused No ConnectionJ2-10 Unused PWM 5/Switch To Gnd 34J2-11 Hoist Lever PWM 1/Switch To Gnd 30J2-12 +8V Sensor Power Supply +8V Sensor Power SupplyJ2-13 Raise Solenoid Proportional Driver No. 10J2-14 Unused Timer In No. 4J2-15 +10V Sensor Power Supply +10V Sensor Power SupplyJ2-16 Unused No ConnectionJ2-17 Unused No ConnectionJ2-18 Body Position Sensor/Body Up Switch PWM 3/Switch To Gnd 32J2-19 Lower Solenoid Proportional Driver No. 9J2-20 Unused UnusedJ2-21 Unused No ConnectionJ2-22 Unused Open Collector Output 3J2-23 Engine Output Speed Timer In No. 2J2-24 Unused UnusedJ2-25 Unused UnusedJ2-26 Unused No ConnectionJ2-27 Unused No ConnectionJ2-28 Neutral Output Open Collector Output 1J2-29 Unused No ConnectionJ2-30 Unused Timer In No. 3QJ2-31 Unused Timer In No. 4QJ2-32 Unused No ConnectionJ2-33 Unused No ConnectionJ2-34 Body Raise Output Open Collector Output 4J2-35 Converter Output Speed Timer In No. 3J2-36 Unused UnusedJ2-37 Back-up Alarm ON/OFF Driver No. 14J2-38 Transmission Output Speed Timer Input No. 1J2-39 Unused No ConnectionJ2-40 Low Steering Warning Output Open Collector Output 2


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785C/789C BRAKE CONTROL PIN IDENTIFICATION


J1- 1 Battery+ (24V) PowerJ1- 2 Battery- (ground) PowerJ1- 3 CAT Data Link- CAT Data Link-J1- 4 Retarder Lamp Proportional Driver No. 2J1- 5 Battery- (ground) PowerJ1- 6 Battery+ (24V) PowerJ1- 7 Solenoid Return Solenoid ReturnJ1- 8 TCS Dash Lamp ON/OFF Driver No. 13*J1- 9 CAT Data Link+ CAT Data Link+J1-10 TCS Right Brake On/Off Solenoid Proportional Driver No. 1J1-11 TCS Left Brake On/Off Solenoid Proportional Driver No. 4J1-12 ARC Control Solenoid Proportional Driver No. 11J1-13 ARC On/Off Switch N/O when Off Switch To Ground 8J1-14 ARC On/Off Switch N/C when Off Switch To Ground 16J1-15 Switch and Sensor Ground Return Switch and Sensor GroundJ1-16 Switch and Sensor Ground Return Switch and Sensor GroundJ1-17 TCS Proportional Servo Valve Proportional Driver No. 3J1-18 ARC Supply Solenoid Proportional Driver No. 12J1-19 TCS System Test Switch Switch To Ground 7J1-20 ARC Pressure Switch Switch To Ground 3J1-21 Location Code 1 (grounded) Switch To Ground 26J1-22 Location Code 0 (open) Switch To Ground 25J1-23 Retarder Switch Switch To Ground 6J1-24 Unused Switch To Ground 2J1-25 Brake Cooling Filter Switch (793C only) Switch To Ground 12J1-26 Brake Overstroke Switch Switch To Ground 13J1-27 Unused Switch To Ground 28J1-28 ECM Location Enable (+Battery) Switch To Battery 3J1-29 Unused Switch To Ground 4J1-30 Unused Switch To Ground 1J1-31 Rear Diff Level Switch Switch To Ground 10J1-32 Rear Diff Filter Switch Switch To Ground 14J1-33 Park Brake Filter Switch Switch To Ground 29J1-34 Unused Switch To Battery 2J1-35 Unused Switch To Ground 5J1-36 Unused Switch To Ground 15J1-37 Unused Switch To Ground 11J1-38 Location Code 2 (open) Switch To Ground 27J1-39 Unused Switch To Ground 9J1-40 +Battery Input Switch To Battery 1*

* The J1-8 driver receives power from the J1-40 input.


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785C/789C BRAKE CONTROL PIN IDENTIFICATION


J2- 1 Rear Diff Fan High Solenoid Proportional Driver No. 6J2- 2 Unused Proportional Driver No. 8J2- 3 Solenoid Return Solenoid ReturnJ2- 4 Left Brake Retract Pressure Sensor PWM 4/Switch To Gnd 33J2- 5 Right Brake Retract Pressure Sensor PWM 2/Switch To Gnd 31J2- 6 Rear Diff Oil Pressure Sensor PWM 6/Switch To Gnd 35J2- 7 Unused Proportional Driver No. 5J2- 8 Unused Proportional Driver No. 7J2- 9 Unused No ConnectionJ2-10 Rear Diff Oil Temperature Sensor PWM 5/Switch To Gnd 34J2-11 Brake System Air Pressure Sensor PWM 1/Switch To Gnd 30J2-12 +8V Sensor Power Supply +8V Sensor Power SupplyJ2-13 Unused Proportional Driver No. 10J2-14 Unused Timer In No. 4J2-15 +10V Sensor Power Supply +10V Sensor Power SupplyJ2-16 Unused No ConnectionJ2-17 Unused No ConnectionJ2-18 Unused PWM 3/Switch To Gnd 32J2-19 Unused Proportional Driver No. 9J2-20 Unused UnusedJ2-21 Unused No ConnectionJ2-22 Unused Open Collector Output 3J2-23 RR Wheel Speed Sensor Timer In No. 2J2-24 Unused UnusedJ2-25 Unused UnusedJ2-26 Unused No ConnectionJ2-27 Unused No ConnectionJ2-28 Unused Open Collector Output 1J2-29 Unused No ConnectionJ2-30 Unused Timer In No. 3QJ2-31 Unused Timer In No. 4QJ2-32 Unused No ConnectionJ2-33 Unused No ConnectionJ2-34 Unused Open Collector Output 4J2-35 Engine Speed Sensor Timer In No. 3J2-36 Unused UnusedJ2-37 Rear Diff Fan Low Solenoid ON/OFF Driver No. 14J2-38 LR Wheel Speed Sensor Timer Input No. 1J2-39 Unused No ConnectionJ2-40 Unused Open Collector Output 2


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MODULE IDENTIFICATION CODES

MID ELECTRONIC CONTROL

36 Engine ECM

27 Transmission/Chassis ECM

116 Brake ECM or Automatic Retarder Control (ARC) orTraction Control System (TCS)

49 VIMS Main Module

57 Interface Module No. 1

58 Interface Module No. 2

FAILURE MODE IDENTIFIER LIST

FMI FAILURE DESCRIPTION

00 Data valid but above normal operational range

01 Data valid but below normal operational range

02 Data erratic, intermittent or incorrect

03 Voltage above normal or shorted high

04 Voltage below normal or shorted low

05 Current below normal or open circuit

06 Current above normal or grounded circuit

07 Mechanical system not responding properly

08 Abnormal frequency, pulse width or period

09 Abnormal update

10 Abnormal rate of change

11 Failure mode not identifiable

12 Bad device or component

13 Out of calibration

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ELECTRONIC UNIT INJECTION (EUI) ENGINE (MID 36)

COMPONENT and SIGNAL CODES

CID FMI DESCRIPTION

01 F05 Cylinder 1--Open Circuit

01 F06 Cylinder 1--Short































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CID FMI DESCRIPTION

91 F08 Throttle Output Signal--Abnormal

100 F03 Oil Pressure Signal--Open/Short to +Battery

100 F04 Oil Pressure Signal--Open/Short to Ground

100 F13 Oil Pressure Sensor--Calibration

101 F03 Crankcase Pressure Signal--Open/Short to +Battery

101 F04 Crankcase Pressure Signal--Open/Short to Ground

101 F13 Crankcase Pressure Sensor--Calibration

110 F03 Coolant Temperature Signal--Open/Short to +Battery

110 F04 Coolant Temperature Signal--Open/Short to Ground

168 F00 Battery Voltage--Above Normal

168 F01 Battery Voltage--Below Normal

168 F02 Battery Voltage--Intermittent

190 F02 Engine Speed/Timing Signal--Lost/Erratic

190 F03 Engine Speed/Timing Signal--Open/Short to +Battery

190 F07 Engine Speed/Timing Sensor--Misinstalled

190 F08 Engine Speed/Timing Signal--Abnormal

248 F09 CAT Data Link--Communication Error

253 F02 Personality Module Mismatch

254 F12 Internal ECM Problem

261 F13 Speed/Timing Sensor--Calibration

262 F03 Analog Supply--Short to +Battery

262 F04 Analog Supply--Short to Ground

263 F03 Digital Supply--Short to +Battery

263 F04 Digital Supply--Short to Ground

267 F02 Ground Level Shutdown Inputs--Incorrect

268 F02 Check Programmable Parameters

273 F00 Turbocharger Outlet Pressure Signal--Above Normal

273 F01 Turbocharger Outlet Pressure Signal--Below Normal

273 F03 Turbocharger Outlet Pressure Signal--Open/Short to +Battery

273 F04 Turbocharger Outlet Pressure Signal--Short to Ground

273 F13 Turbocharger Outlet Pressure Sensor--Calibration

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CID FMI DESCRIPTION

274 F03 Atmospheric Pressure Signal--Open/Short to +Battery

274 F04 Atmospheric Pressure Signal--Short to Ground

274 F13 Atmospheric Pressure Sensor--Calibration

275 F03 Right Turbocharger Inlet Pressure Signal--Open/Short to +Battery

275 F04 Right Turbocharger Inlet Pressure Signal--Short to Ground

275 F13 Right Turbocharger Inlet Pressure Sensor--Calibration

276 F03 Left Turbocharger Inlet Pressure Signal--Open/Short to +Battery

276 F04 Left Turbocharger Inlet Pressure Signal--Short to Ground

276 F13 Left Turbocharger Inlet Pressure Sensor--Calibration

291 F05 Engine Fan Solenoid--Open Circuit

291 F06 Engine Fan Solenoid--Short to Ground

296 F09 CAT Data Link Communications Error with Transmission Control

338 F05 Pre-lubrication Relay--Open Circuit

338 F06 Pre-lubrication Relay--Short to Ground

338 F11 Pre-lubrication Relay--Timeout

526 F05 Wastegate Solenoid--Open Circuit (793 only)

526 F06 Wastegate Solenoid--Short to Ground (793 only)

542 F03 Unfiltered Oil Pressure Signal--Open/Short to +Battery

542 F04 Unfiltered Oil Pressure Signal--Short to Ground

542 F13 Unfiltered Oil Pressure Sensor--Calibration

544 F08 Engine Fan Speed Signal--Abnormal

545 F05 Ether Injection START Relay--Open/Short to +Battery

545 F06 Ether Injection START Relay--Short to Ground

546 F05 Ether Injection HOLD Relay--Open/Short to Ground

546 F06 Ether Injection HOLD Relay--Short to +Battery

569 F05 Oil Renewal Solenoid--Open/Short to +Battery

569 F06 Oil Renewal Solenoid--Short to Ground

800 F09 VIMS Communications Error

827 F08 Left Exhaust Temperature Abnormal

828 F08 Right Exhaust Temperature Abnormal

829 F03 Rear Aftercooler Temperature Signal--Open/Short to +Battery

829 F04 Rear Aftercooler Temperature Signal--Short to Ground

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TRANSMISSION/CHASSIS ECM (MID 27)


CID FMI DESCRIPTION

168 F01 System Voltage--Low

177 F03 Transmission Oil Temperature Sensor--Open/Shorted to +Battery

177 F04 Transmission Oil Temperature Sensor--Shorted to Ground

190 F02 Engine Output Speed (EOS) Signal--Lost/Erratic

248 F09 CAT Data Link Communication Error

269 F00 Sensor Power Supply--Shorted to +Battery

269 F01 Sensor Power Supply--Shorted to Ground

378 F03 Auto Lube Solenoid (grease)--Shorted to +Battery

378 F05 Auto Lube Solenoid (grease)--Open

378 F06 Auto Lube Solenoid (grease)--Shorted to Ground

444 F03 Start Relay--Short to +Battery

444 F05 Start Relay--Open Circuit

444 F06 Start Relay--Short to Ground

590 F09 Engine Control Module--Missing on Data Link

590 F12 Engine Control Module--Device Bad

627 F03 Parking/Secondary Brake Pressure Switch--Open/Short to +Battery

627 F04 Parking/Secondary Brake Pressure Switch--Short to Ground

672 F02 Converter Output Speed (COS) Signal--Lost/Erratic

700 F02 Transmission Gear Switch--Invalid

701 F02 Transmission Output Speed (TOS) Signal--Lost

701 F08 Transmission Output Speed (TOS) Signal--Erratic

701 F11 Transmission Output Speed (TOS) Signal--Not Identifiable

702 F02 Gear Selector Lever--Invalid

704 F03 Service Brake Pressure Switch--Open/Short to +Battery

704 F04 Service Brake Pressure Switch--Short to Ground

707 F03 Upshift Solenoid--Shorted to +Battery

707 F05 Upshift Solenoid--Open

707 F06 Upshift Solenoid--Shorted to Ground

708 F03 Downshift Solenoid--Shorted to +Battery

708 F05 Downshift Solenoid--Open

708 F06 Downshift Solenoid--Shorted to Ground

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TRANSMISSION/CHASSIS ECM (MID 27)


CID FMI DESCRIPTION

709 F03 Lockup Solenoid--Shorted to +Battery

709 F05 Lockup Solenoid--Open

709 F06 Lockup Solenoid--Shorted to Ground

724 F03 Hoist Raise Solenoid--Shorted to +Battery

724 F05 Hoist Raise Solenoid--Open

724 F06 Hoist Raise Solenoid--Shorted to Ground

725 F03 Hoist Lower Solenoid--Shorted to +Battery

725 F05 Hoist Lower Solenoid--Open

725 F06 Hoist Lower Solenoid--Shorted to Ground

773 F03 Hoist Lever Sensor--Open/Shorted to +Battery

773 F04 Hoist Lever Sensor--Shorted to Ground

800 F09 VIMS--Missing on Data Link

800 F12 VIMS--Device Bad

826 F03 Torque Converter Oil Temperature Sensor--Open/Shorted to +Battery

826 F04 Torque Converter Oil Temperature Sensor--Shorted to Ground

967 F02 Machine Application Identity--Erratic

967 F09 Machine Application Identity--Missing on Data Link

1175 F03 Body Position Sensor--Open/Shorted to +Battery

1175 F06 Body Position Sensor--Shorted to Ground

1236 F03 Body Up Dash Lamp--Short to +Battery

1236 F06 Body Up Dash Lamp--Short to Ground

1326 F02 Location Code--Incorrect

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BRAKE ECM (MID 116)

AUTOMATIC RETARDER CONTROL (ARC)

TRACTION CONTROL SYSTEM (TCS)


CID FMI DESCRIPTION

84 F02 Ground Speed Signal--Lost/Erratic

84 F09 Ground Speed Signal--Missing on Data Link

91 F09 Throttle Sensor--Missing on Data Link

100 F03 Engine Speed Cross Check--Incorrect

168 F01 System Voltage--Low

190 F02 Engine Output Speed (EOS) Signal--Lost/Erratic

190 F08 Engine Output Speed (EOS) Signal--Abnormal

190 F09 Engine Output Speed (EOS) Signal--Missing on Data Link

248 F09 CAT Data Link--Communication Error269 F00 Sensor Power Supply--Shorted to +Battery

269 F01 Sensor Power Supply--Shorted to Ground

296 F09 Transmission Control--Missing on Data Link

541 F03 Differential (Axle) Oil Pressure Sensor--Open/Shorted to +Battery

541 F04 Differential (Axle) Oil Pressure Sensor--Shorted to Ground

607 F02 Left Rear Wheel Speed Sensor Signal--Lost/Erratic

608 F02 Right Rear Wheel Speed Sensor Signal--Lost/Erratic

627 F09 Parking/Secondary Brake Pressure Switch--Missing on Data Link

689 F03 TCS Left Solenoid--Shorted to +Battery

689 F05 TCS Left Solenoid--Open

689 F06 TCS Left Solenoid--Shorted to Ground

690 F03 TCS Right Solenoid--Shorted to +Battery

690 F05 TCS Right Solenoid--Open

690 F06 TCS Right Solenoid--Shorted to Ground

700 F09 Transmission Gear Switch--Missing on Data Link

702 F09 Gear Selector Lever--Missing on Data Link

704 F09 Service/Retarder Brake Pressure Switch--Missing on Data Link

710 F03 ARC Supply Solenoid--Shorted to +Battery

710 F05 ARC Supply Solenoid--Open

710 F06 ARC Supply Solenoid--Shorted to Ground

710 F12 ARC Supply Valve--Malfunction

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BRAKE ECM (MID 116)

AUTOMATIC RETARDER CONTROL (ARC)

TRACTION CONTROL SYSTEM (TCS)


CID FMI DESCRIPTION

711 F03 ARC Control Solenoid--Shorted to +Battery

711 F05 ARC Control Solenoid--Open

711 F06 ARC Control Solenoid--Shorted to Ground

711 F07 ARC Control Valve--Mechanical Response Malfunction

711 F12 ARC Control Valve--Malfunction

712 F03 Retarder Dash Lamp--Shorted to +Battery

712 F06 Retarder Dash Lamp--Shorted to Ground

713 F03 ARC ON/OFF Switch--Open or Shorted to +Battery

713 F04 ARC ON/OFF Switch--Shorted to Ground

714 F03 ARC Pressure Switch--Open or Shorted to +Battery

715 F03 Retarder Pressure Switch--Open or Shorted to +Battery

719 F03 TCS Proportional Solenoid--Shorted to +Battery

719 F05 TCS Proportional Solenoid--Open

719 F06 TCS Proportional Solenoid--Shorted to Ground

966 F03 TCS Dash Lamp--Shorted to +Battery

966 F06 TCS Dash Lamp--Shorted to Ground

796 F03 Differential Fan HI Solenoid--Shorted to +Battery

796 F05 Differential Fan HI Solenoid--Open

796 F06 Differential Fan HI Solenoid--Shorted to Ground

800 F09 VIMS--Missing on Data Link

835 F03 Differential (Axle) Oil Temperature Sensor--Open/Shorted to +Battery

835 F04 Differential (Axle) Oil Temperature Sensor--Shorted to Ground

849 F03 System Air Pressure Sensor--Open/Shorted to +Battery

849 F04 System Air Pressure Sensor--Shorted to Ground

967 F02 Machine Application Identity--Erratic

967 F09 Machine Application Identity--Missing on Data Link

1225 F03 Left Park Brake Oil Pressure Sensor--Open/Shorted to +Battery

1225 F04 Left Park Brake Oil Pressure Sensor--Shorted to Ground

1226 F03 Right Park Brake Oil Pressure Sensor--Open/Shorted to +Battery

1226 F04 Right Park Brake Oil Pressure Sensor--Shorted to Ground

1326 F02 Location Code--Incorrect

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VIMS KEYPAD OPERATIONS

The keypad allows the operator or a service technician to interact with the VIMS. Some of thefunctions that can be performed by the keypad are:

PAYCONF 7292663 Configure Payload Monitor

PAYCAL 729225 Calibrate Payload Monitor

TOT 868 Show Payload Cycle Resettable Totals

RESET 73738 Reset Displayed Data

SVCLIT 782548 Reset Service Light

SVCSET 782738 Service Light Set

TEST 8378 Self Test Instrumentation

MSTAT 67828 Show Machine Statistics (source and configuration codes)

LUBSET 582738 Set Lube Cycle Times

LUBMAN 582626 Manual Lube

EACK 3225 Show Acknowledged Events (Active)

ESTAT 37828 Show Event Statistics

ELIST 35478 Show Event List (Intermittent)

EREC 3732 Start Event Recorder

ERSET 37738 Configure 1 Event Recorder(requires VIMS PC connection)

DLOG 3564 Start/Stop Data Logger

DLRES 35737 Reset Data Logger

LA 52 Change Language

UN 86 Change Units

ODO 636 Odometer Set/Reset(requires VIMS PC connection)

BLT 258 Change Backlight

CON 266 Change Display Contrast

OK Key: Used to complete keypad entries and to acknowledge events. Acknowledging an event willremove the event from the display temporarily. Severe events cannot be acknowledged.

GAUGE Key: Displays parameters monitored by the VIMS. Depressing the arrow keys will scrollthrough the parameters. Entering the parameter number and the GAUGE key selects that parameter.

F1 Key: Provides additional information on the current event being displayed. For MAINTENANCEevents, the MID, CID, and FMI are displayed. For DATA events, the current parameter value isdisplayed (temperature, pressure, rpm).

SESV1706 Printed in U.S.A.11/98

manual 789c - 785c

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