p02 C Brake Master

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21 C Series

Wheel Loaders

21C Series Wheel Loaders

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CASE CORPORATION 2002 Case Corporation

700 STATE STREET All Rights Reserved

RACINE, WI 53404 U.S.A.

CASE CANADA CORPORATION

450 SHERMAN AVENUEHAMILTON, ON L8N 4C4 CANADA

Printed in U.S.A.


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Table of Contents

NOTES......................................................................................................................6

BRAKE CIRCUIT FROM PUMP TO TREADLE VALVE..........................................7

BRAKE CIRCUIT TO AXLES...................................................................................8

PARKING BRAKE ...................................................................................................9

PRESSURE TEST POINTS FOR THE ACCUMULATORS AND PILOTCONTROL...............................................................................................................10

BRAKE CIRCUIT....................................................................................................11

ALL "C" SERIES................... .................... .................... .................... ..................... ...... ...... ...... .. 11General description ...............................................................................................................11Circuit Description .......................................................................................................... ...... 11

BRAKE PUMP........................................................................................................12

ALL "C" SERIES................... .................... .................... .................... ..................... ...... ...... ...... .. 12Brake pump description ........................................................................................................ 12

DUAL ACCUMULATOR CHARGING VALVE ASSEMBLY..................................14

ALL "C" SERIES................... .................... .................... .................... ..................... ...... ...... ...... .. 14General description ...............................................................................................................14Circuit description ................................................................................................................. 14Description of the Relief Valve.............................................................................................. 14Description of Cut In and Cut out Spool Function....................................................... ..........14Cut-in spool............................................................................................................................ 14


Cut-out spool..................................................................................................................... .... 15Description of the Filter, Orifice and Check Valve.................................................................15Description of Accumulator Isolation Poppet.........................................................................15


Description of the Accumulator Charging Pressure Switch...................................................16

NOTES....................................................................................................................19

HYDRAULIC MULIT-FUNCTION VALVE..............................................................20

(COMBINATION VALVE).......................................................................................20

ALL "C" SERIES................... .................... .................... .................... ..................... ...... ...... ...... .. 20

General Description............................................................................................................... 20Operation Description............................................................................................................ 20Operation Description (Pressure Switches)........................................................................... 20Flow to the Accumulators and Pressure Switches.................................................................20



Operation Description (Parking Brake).................................................................................. 21


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Flow to the Parking Brake Solenoid Valve..................................................................... .......22Parking Brake Description.................................................................................................... .22Operation Description (Pressure Reducing Valve)................................................................22



Flow to the Pressure Reducing Valve....................................................................................23Pressure Reducing Description..............................................................................................23

Auxiliary Hydraulics Description............................................................................................ 23Operation Description (Pilot Lockout Solenoid) ....................................................................23



Flow to the Pilot Lockout Solenoid........................................................................................ 24Pilot Lockout Solenoid Description........................................................................................ 24

PARKING BRAKE .................................................................................................32

GENERAL DESCRIPTION.............................................................................................................32TESTINGTHE PARK BRAKE........................................................................................................32

TOWING THE WHEEL LOADER...........................................................................33

TROUBLESHOOTING THE PARKING BRAKE....................................................34

PARK BRAKE INFORMATION CENTER OUTPUT CHECK...................................................................34PARK BRAKE SWITCH CHECK.....................................................................................................35REDUNDANT BRAKE PRESSURE SWITCH CHECK..........................................................................36

SERVICE BRAKE FOOT SWITCH CHECK.......................................................................................37REQUESTED GEAR CHECK.........................................................................................................38ACTUAL GEAR STATUS..............................................................................................................39

ACCUMULATORS.................................................................................................40

ALL "C" SERIES................... .................... .................... .................... ..................... ...... ...... ...... .. 40General description ...............................................................................................................40Circuit description ................................................................................................................. 40

BRAKE TREADLE VALVE.....................................................................................42

ALL "C" SERIES.............................. .................... ..................... .................... ........... ...... ...... ... 42General Description .............................................................................................................. 42Operation Description............................................................................................................ 42

Flow to the Brake Pedal.........................................................................................................42NOTES....................................................................................................................45

DISK BRAKE ASSEMBLIES..................................................................................46

621C, 721C,AND 821C............................................................................................................46General Description............................................................................................................... 46Operation Description............................................................................................................ 46



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921C......................... ..................... .................... .................... .................... .................... ...... ... 48General Description............................................................................................................... 48Operation Description............................................................................................................ 48



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NOTES


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Brake Circuit from Pump to Treadle Valve


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Brake Circuit to Axles


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Parking Brake


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Pressure Test Points for the Accumulators and Pilot Control


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Brake Circuit

All "C" Series

General description

On all "C" Series Wheel Loaders, the brake pump provides hydraulic oil for thebrakes, the pilot valve(s), and the optional ride control and/or coupler lockingvalve. The hydraulic oil is drawn through a suction hose from the tube that feedsthe main pumps.

Circuit Description

The pump which is mounted to the auxiliary drive on the front cover on the leftside of the engine, is operational whenever the engine is running. The hydraulicoil is drawn through a suction hose connected to the tube that feeds the mainpump. It then flows through the main components of the brake circuit.

The dual accumulator charging valve assembly controls the maximum pressureand unloads when the maximum pressure is obtained. As the stand-by oil is usedup, the low-pressure side of the dual accumulator charging valve assembly will cutback in and replenish the system pressure.

The accumulators are used to provide a surplus of oil under pressure. Theaccumulators will provide oil for the brakes and pilot valve(s) when the pump isunloaded and dumping oil to the sump or if the engine is dead.

The Hydraulic Mulit-function valve controls the flow of oil to the parking brake andthe pilot valve(s) while at the same time controlling the pressure to the pilot

valve(s).

The brake pedal valve regulates the flow of oil to the brake piston in the axleends.The brakes used on the "C" SERIES are internal wet disk brakes that are locatedinside the axle.


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Brake Pump

All "C" Series

Brake pump description

The brake pump is a Commercial Intertech gear pump. The pump delivers 7.6GPM (28.8 LPM) at a rated engine speed of 2200 RPM. The pump rotates in acounter-clockwise direction as seen from the shaft end. Because the pump is apositive displacement pump, the flow output varies with the engine speed. Thepump is operational whenever the engine is running, and is either charging theaccumulators or returning flow to the reservoir.

The performance of the pump can be determined by installing a flow meterbetween the outlet of the pump and the hydraulic reservoir. The flow rate with andwithout pressure can then be determined.


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621C721C

821C921C Brake Pump


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Dual Accumulator Charging Valve Assembly

All "C" Series

General description

The Dual Accumulator Charging Valve Assembly is mounted on the right sideplate of the rear chassis. It is designed to control the oil pressure from the brakepump and to maintain a supply of oil for the accumulators, brakes, and pilot valvecircuits.

Circuit description

The oil from the brake pump enters Dual Accumulator Charging Valve Assembly.It passes the pressure relief valve; then through the valve cut-in spool, the filter,the orifice, the check valve, the cut-out spool, and the accumulator isolationpoppet spool. Upon leaving the Dual Accumulator Charging Valve Assembly, theoil flows to the Hydraulic Mulit-function Valve.

Description of the Relief Valve

A relief valve at the inlet of the Dual Accumulator Charging Valve Assemblyprotects the system from excessive pressures. In the event something fails in thebrake circuit and the pressure builds to 3000 PSI (20684 kPa), the relief valve willshift and divert all output from the brake pump through the return port. This oilflows through the two 10-micron filters and back to the reservoir.

Description of Cut In and Cut out Spool Function

Cut-in spool

The oil from the brake pump flows through the cut-in spool. It also provides pilotpressure to the cut-in spool on the side opposite of the spring. The oil that flowsthrough the cut-in spool also flows through the cut-out spool and provides pilotpressure on the spring side of the cut-in spool. This equalizes the pressure on thecut-in spool so the spring pressure will hold the spool in a shifted position;therefore, allowing the oil to pass through the spool. When the pilot pressure onthe spring side is allowed to return to the reservoir, because of the cut-out spoolshifting, the cut-in spool will shift and allow the brake pump flow to return to the

reservoir.


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(Cont.)

Cut-out spool

The oil from the brake pump flows through the cut-in spool and provides pilotpressure on the end of the cut-out spool opposite the spring. When this pressurereaches 2800 PSI, the spool will shift and allow the pilot pressure on the springside of the cut-in spool to return to the reservoir.

While both the cut-in and cut-out spools are shifted. The oil is allowed to flowthrough the cut-in spool, but it is blocked from flowing through the cut-out spool.The oil is also blocked from going to the accumulators by the check valve; there is2800 PSI of pressure holding the check valve closed. The cut-out spool remainsshifted until the pilot pressure is reduced to approximately 2000 PSI (13790 kPa);this will occur by applying the brakes or through system leakage. When thepressure falls to 2000 PSI (13790 kPa), the spring shifts the cut-out spool andallows oil to flow through to again, providing pilot pressure on the spring side ofthe cut-in spool. This equalizes the pressure on the cut-in spool, allowing thespring to shift the spool; therefore, preventing the oil from passing through thereturn port.

Description of the Filter, Orifice and Check Valve

Between the cut-in spool and the cut-out spool, the oil passes through the 54-micron filter, the orifice, and the check valve. The 54-micron filter protects thebraking circuit from impurities contained in the oil. The orifice slows the oil and

reduces the shock pressure on the accumulator when they are refilled. The checkvalve blocks oil from the accumulators from flowing back through the cut-in spool,after it shifts, and returning to the reservoir.

Description of Accumulator Isolation Poppet

The poppet has pilot pressure and a centering spring on one end, and pilotpressure only on the other end. An accumulator provides the spring end pilotpressure. Pilot pressure on the opposite end, is provided by the brake pump. Thepoppet does not completely block off the passageway nor does it completely openthe passageway. Their purpose is to isolate one brake circuit if the other fails.

When both brake circuits are working, the poppet will be centered in thepassageway and allow oil to flow between the accumulators. As the pressure in anaccumulator falls it reduces the pilot pressure in that solenoid, this will cause the


(Cont.)

poppet to be moved by the pump pressure, open the passageway, and allow moreoil to the low accumulator. If one brake circuit would fail the pressure and spring


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on the opposite circuit would shift the poppet and act as a check valve; keepingpressure in the working circuit.

Description of the Accumulator Charging Pressure Switch

The accumulator charging pressure switch is set at 1700 PSI (11721 kPa). If the

accumulator charging pressure drops down to this point, the Stop Master Indicator(Red) illuminates and the alarm sounds continuously, indicating a brake systemproblem. This condition will be written into diagnostic memory if the engine isrunning at 700 RPM or above for 15 seconds


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1. 2000 psi Cut-in Spool 6. Brake Pump Inlet2. Outlets to accumulators 7. Accumulator Isolation Poppet Spool3. Check Valve Assembly 8. 3000 psi Relief Valve4. Bronze Filter 9. 2800 psi Cut-out Spool5. 1700 psi Pressure switch Port 10. Brake Pressure Adjustment


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1. 2000 psi Cut-in Spool 6. Brake Pump Inlet2. Outlets to accumulators 7. Accumulator Isolation Poppet Spool3. Check Valve Assembly 8. 3000 psi Relief Valve4. Bronze Filter 9. 2800 psi Cut-out Spool5. 1700 psi Pressure switch Port 10. Brake Pressure Adjustment


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NOTES


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Hydraulic Mulit-function Valve

(Combination Valve)

All "C" Series

General Description

This valve is mounted on the right rear frame near the articulation joint. It controlsthe Parking Brake, the Pilot Valve Lock Out, and the pressure for the Pilot Valves.

At the same time, it provides a passage for filling the brake accumulators andmonitoring the pressure to warn the operator if there is a failure in the brakesystem.

Operation Description

Because this is a dual braking system, the oil going to the Front Brakes flowsdirectly from the Dual Accumulator Charging Valve Assembly into one each of theBrake Accumulators, the Redundant Brake Pressure Switches then the BrakeTreadle Valve. Oil going to the Rear Brakes flows directly to the other Brake

Accumulator, the Redundant Brake Pressure Switch, and then the Brake TreadleValve. Oil for the Rear Brakes also supplies oil for the Parking Brake, and afterpassing through the Pilot Pressure Reduction Valve, supplies oil to the PilotValves and the options Ride Control and/or Coupler Locking Valve.

Operation Description (Pressure Switches)

The Brake Pressure Switch for the front and rear brakes is set for 900 PSI (6205kPa). If both of the accumulators drop below this pressure, a severe brakemalfunction has occurred. The Transmission ECM (Electronic Control Module) willdisconnect the transmission from the engine, and the drive train will beneutralized. At this point, the Parking Brake will be applied, and the ParkingBrake Lamp on the Instrument Cluster will illuminate.

Flow to the Accumulators and Pressure Switches

Oil flows from the Dual Accumulator Charging Valve Assembly into the HydraulicMulit-function Valve through port FB for the front brake circuit and RB for the rearbrake circuit.

Port FB (front brake) is connected directly to ports ACF for the accumulator andPS1F for the pressure switch. Hydraulic tubing connects the accumulator to port

ACF. The Redundant Brake Pressure Switch is threaded directly into the PS1Fport.


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(Combination Valve)

(Cont.)

Port RB (rear brake) is connected directly to ports ACR for the accumulator andPS1R for the pressure switch. Hydraulic tubing connects the accumulator to port

ACR. The Redundant Brake Pressure Switch is threaded directly into the PS1Rport.

Port RB is also connected internally to the other valves and through them to theother outlet ports.

Operation Description (Parking Brake)

The parking brake is spring applied and hydraulically released. When the

machine is turned off, the parking brake is automatically applied. When themachine is started, the parking brake stays on, and the parking brake lamp on theInstrument Cluster will illuminate. The operator must press the service brakepedals and put the machine in gear before the parking brake will release. If theoperator puts the machine in gear before pressing the service brake pedals, theCaution Master Indicator (Yellow) will flash and the alarm will sound for three (3)seconds.

If the machine loses electricalpower, the parking brake activates automatically.

If the machine loses hydraulicpressure, the parking brake will not applybecause the internal check valve will keep the parking brake canister pressurizeduntil the solenoid valve is shifted.


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(Combination Valve)

(Cont.)

Flow to the Parking Brake Solenoid Valve

Oil flows into port RB, past the internal Check Valve (cartridge type), to theParking Brake Solenoid Valve.

Parking Brake Description

The Parking Brake circuit consists of two Solenoid Valves, both are two way, twoposition cartridge valves. One contains a check valve, which controls the

disengagement of the parking brake, and the second one controls the flowdirection during engagement and disengagement. These screw-in hydrauliccartridge valves are installed in the PB port of the valve block body.

When the electrical current is removed, the solenoid's magnetic field collapses,and the spring on the opposite side shifts the valve. When the valve shifts, the oiltrapped in the parking brake canister flows to reservoir, and the spring then setsthe parking brake.

When the electrical current is applied, the solenoid's magnetic field energizes,and the solenoid overcomes the spring pressure and shifts the valve. When thevalve shifts, the oil flows through the valve and out of port PB (parking brake) intothe brake canister, depressing the spring and releasing the parking brake.

Operation Description (Pressure Reducing Valve)

The Pressure Reducing Valve controls the pressure for the auxiliary hydraulicoptions and the Pilot Valves. The valve senses circuit pressure, and when itreaches 550 PSI, the valve shifts and blocks the flow until it senses the pressurehas dropped. The spring shifts the spool, allowing flow to the auxiliary and pilothydraulics. In the cavity beneath the pressure reducing valve there is a flow-limiting orifice disc with a .063 diameter drilled pilot opening. This openingprovides a minimum pressure drop between the Pressure Reducing Valve and the

hydraulic down stream. This difference in pressure allows the pilot valve tooperate without jerking.


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(Combination Valve)

(Cont.)

Flow to the Pressure Reducing Valve

Oil flows into port RB and flows through the Pressure Reducing Valve as long asthe pressure in the circuit is less than 550 PSI.

Pressure Reducing Description

This valve is a spool-type direct acting, hydraulic Pressure Reducing Valve withan internal spring chamber drain. It is a pressure-regulating device for secondarycircuits. This valve is installed in port PR of the valve block body

Auxiliary Hydraulics DescriptionThe auxiliary port (AUX) in the valve block body is blocked unless auxiliaryhydraulics are installed (ride control, coupler locking). If installed, they will havetheir own control valves added between the pressure reducing valve and theoption.

Operation Description (Pilot Lockout Solenoid)

The Pilot Lockout Switch is located on the top left-hand side of the Front Console.Press the left side of the toggle switch disables the Pilot Controls. The PilotControl Lamp, which is located on the left side of the Instrument Panel, will

illuminate.

When activated, the Pilot Lockout Switch disconnects the electrical current to thePilot Lockout Solenoid Valve. The magnetic field in the coil collapses and thespring on the opposite side of the valve shifts the spool blocking all oil flow to thePilot Valves. When the Pilot Valves are disabled, the loader linkage is locked inthe position they were in when the switched was pressed.Pressing the right side of the toggle switch enables the Pilot Controls. The PilotControl Lamp, which is located on the left side of the Instrument Panel, will notilluminate.

When the Pilot Lockout Switch is activated, it connects the electrical current to thePilot Lockout Solenoid Valve. The magnetic field in the coil energizes and over


(Combination Valve)

(Cont.)


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comes the spring on the opposite side of the valve. The spool shifts, allowing theoil to flow to the Pilot Valves. When the Pilot Valves are enabled, the loaderlinkage will operate when the control levers are moved.

Flow to the Pilot Lockout Solenoid

Oil flows in port RB, through the Pressure Reducing Valve and orifice disc, to theblocked port on the Pilot Lockout Valve.

Pilot Lockout Solenoid Description

This is a solenoid-operated, normally closed, two-way, direct-acting spool valve.This valve is installed in port SV1 of the valve block body.


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Parking Brake

General Description

The park brake is activated as soon as the electrical current is turned off. To

release the park brake the operator must; start the machine, step on the servicebrake, and shift into either forward or reverse.

Testing the Park Brake

The operator can test the park brake by using the diagnostics built into theinformation center. The transmission must be in 3rd gear manual mode to performthe test. If the transmission is left in any other gear during the test thetransmission will be disconnected from the engine. To perform the test use thefollowing procedure:

1. Start the machine.

2. Make sure the transmission selector switch is in 3rd neutral, the automaticswitch is in the manual position, and the park brake switch is on.

3. Select the display field number 011 using the programming entry procedurelisted previously.

4. Press the up count switch once so the display reads 1.

5. Shift the transmission selector into 3rd forward and slowly increase the engineRPM's. The park brake should hold the machine at full throttle.

6. Shift the transmission selector into 3rd reverse and slowly increase the engineRPM's. The park brake should hold the machine at full throttle.

7. Reduce the engine RPMs and shift the machine into neutral.

8. Press the reset switch to exit the test mode.

9. Turn off the machine.

If the park brake does not hold the machine at full throttle refer to the brakes

section of the service manual for troubleshooting procedures.


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Towing the Wheel Loader

If you must tow the Wheel Loader, read the following recommendations and usecaution.

NEVER Tow the Wheel Loader from the Front.

If the Wheel Loader cannot be started to release the parking brake, do thefollowing:1. Put blocks in front of and behind each tire.

2. Remove the Parking brake cap (6).

3. Loosen the lock nut (9).

4. Turn the adjusting screw COUNTERCLOCKWISE until the parking brake is

released (10).

If the Wheel Loader is to be towed more than 1/2 mile (0.8 km) you mustdisconnect the front and rear drive shafts.


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Troubleshooting The Parking Brake

If the park brake does not release, perform the following checks.

Park Brake Information Center Output Check

This check will check the wiring from the information center to the park brake relayto make sure that it is functioning properly. This same check will also check tosee that the park brake indicator light is functioning.


2. Press the Program/Reset switch to the program position, advance to displayfield number 019, the park brake light will flash intermittently.

3. Press the Program/Reset switch back to the center position. You should see a01 in the display if the information center is not activating the park brake relayand the park brake is in the on position.

4. Turn the park brake switch in the cab to the off position, place or foot on theservice brake and shift the FNR lever to either forward or reverse. You shouldsee the display read 00 when the park brake releases.

5. Place the FNR lever back in neutral, place the park brake switch in the onposition.

6. Press the Program/Reset switch to the Reset position to exit the monitoring

mode.

7. Turn the key switch to the off position.


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Park Brake Switch Check

This check will check operation of the park brake switch to make sure that it isfunctioning properly. This same check will also check to see that the park brakeindicator light is functioning. This check does not check the wiring from the

information center to the park brake pressure switch.

1. Turn the key switch to the on position, do not start the machine.


3. Press the Program/Reset switch back to the center position. You should see a01 in the display if the park brake switch is in the on position.

4. Toggle the park brake switch to the off position. You should see the display

read 00 when the park brake releases .

5. Press the Program/Reset switch to the Reset position to exit the monitoringmode.



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Redundant Brake Pressure Switch Check

This check will check operation of the redundant brake pressure switch (900 psi)and the wiring from the switch to information center to make sure that it isfunctioning properly. This same check will also check to see that the park brake

indicator light is functioning. This check does not check the wiring from theinformation center to the park brake switch located in the cab.



3. Press the Program/Reset switch back to the center position. You should see a00 in the display if the brake pressure is in the normal operating range. Thedisplay will show 01 if the brake pressure is out of the normal operating range.




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Service Brake Foot Switch Check

This test will check operation of the service brake foot switch to make sure that itis functioning properly. This same check will also check to see that the park brakeindicator light is functioning.



3. Press the Program/Reset switch back to the center position. You should see a00 in the display if the service brake pedals are not activated.

4. Step on the service brake pedal. You should see a 01 in the display when theswitch is activated.




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Requested Gear Check

This test is designed to test the FNR/Shifting lever to see that it is functioningnormally. It tests to see that the information center is reading the same gear thatthe lever is requesting.


2. Press the Program/Reset switch to the program position, advance to displayfield number 028

3. Press the Program/Reset switch back to the center position. You should seethe appropriate code in the table below for the requested gear. The displayshould also flash the appropriate direction selected and gear number in thetransmission display window.

4. Cycle through all gears in all directions (FNR) using the shifter lever and makesure the appropriate code is shown on the display for each gear requested.The correct codes are listed in the table below.

Forward 1 - Code 101 Neutral 1 Code 200 Reverse 1 Code 301

Forward 2- Code 102 Neutral 2 Code 200 Reverse 2 Code 302

Forward 3- Code 103 Neutral 3 Code 200 Reverse 3 Code 303Forward 4- Code 104 Neutral 4 Code 200




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Actual Gear Status

This test will check to determine that the actual gear the transmission is in, is thesame as the gear that the information center is reading. It does not test thereadings that the information center is receiving from the FNR/Shifter lever. To

perform this test the operator must have the transmission in the manual mode, thedeclutch and park brake switch off, and apply the service brake.


2. Press the Program/Reset switch to the program position, advance to displayfield number 030 using the programming entry procedure listed previously.

3. Press the Program/Reset switch back to the center position. You should seethe appropriate code in the table below for the requested gear the transmissionis in. The display should also flash the appropriate direction selected and gear

number in the transmission display window.

4. Cycle through all gears in all directions (FNR) using the shifter lever and makesure the appropriate code is shown on the display for each gear requested.The correct codes are listed in the table below.

Forward 1 - Code 101 Neutral 1 Code 200 Reverse 1 Code 301Forward 2- Code 102 Neutral 2 Code 200 Reverse 2 Code 302

Forward 3- Code 103 Neutral 3 Code 200 Reverse 3 Code 303

Forward 4- Code 104 Neutral 4 Code 200Limp Home Mode 115 Limp Home Mode 215 Limp Home Mode - 315


6. Stop the machine, place it in neutral and apply the park brake.



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Accumulators

All "C" Series

General description

Two accumulators are used in the brake system. One serves the front axlebrakes; the other is used for the rear axle brakes. The accumulators on the brakesystem hold the pressure required to operate the brakes. In addition, they holdreserve pressure to operate the brakes and pilot control valve(s) in the event thebrake system or the engine has a malfunction.

Circuit description

The accumulators are charged to 800 PSI (5516 kPa) with nitrogen. When

hydraulic oil is applied to the opposite side of the accumulator piston at pressuresin excess of 800 PSI (5516 kPa), the accumulator piston moves, compressing thenitrogen while accumulating a supply of oil. The Dual Accumulator ChargingValve Assembly charges the accumulators to 2800 PSI (19305 kPa) when themachine is started or when the accumulator pressures are reduced because ofbrake usage or system leakage. When the brakes are applied, hydraulic pressurein the accumulator is and, the volume of oil in the accumulator is also reduced. Asthe pressure nears 2000 PSI (13790 kPa), the accumulators are resupplied withBrake Pump flow from the Dual Accumulator Charging Valve Assembly.

If the front brakes malfunction in the dual brake system, the rear brakes will stillbe operational. Conversely, if the rear brakes malfunction, the front brakes will

still be operational.


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Brake Treadle Valve

ALL "C" SERIES

General Description

The Brake Treadle Valve consists of two pressure regulating valves that controlthe flow of oil from the accumulators to the brake actuators. Each valve assemblycontrols the brakes on one axle, yet a single pedal actuates both, resulting in theapplication of all four brakes from the single pedal.


The Brake Treadle Valve is actuated as the operator depresses the pedal. Theharder the operator depresses the pedal, the more the brake treadle valve moves.The further the Brake Treadle Valve moves, the higher the brake pressure is atthe wheel. As the pressure in the brake actuators begins build, it is sensedbetween and beneath the spools in the valve. This creates an increase in pedaleffort that provides pedal "feel."

The left brake pedal contains the Brake Treadle Valve and electrical switches forthe brake lamp and the transmission declutch. The right brake pedal is a tag-along. The two brake pedals are attached with a cross shaft. This solidconnection allows the operator to depress either pedal to operate the brakes. Italso allows the operator to declutch the transmission with either pedal afteractivating the declutch switch.

Flow to the Brake PedalThe oil flows from the Dual Accumulator Valve Assembly to the Brake TreadleValve. The accumulators are attached to this circuit also and provide oil pressureas needed when the brakes are applied.


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NOTES


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Disk Brake Assemblies

621C, 721C, and 821C

General Description

The 621C, 721C, and 821C use a ZF limited slip axle. This axle was adopted asupgrade to the wet disc brakes on the "B" Series. The ZF axle model numbers areas follows:

621C 721C 821C

Rear Front Rear Front Rear Front

407 407 407 409 409 411

Each of the four brake assemblies is mounted in the planetary assembly.

The brake pressure can be checked at the quick disconnect fitting. The quickdisconnect fittings are located on the right side of the unit near the pivotconnection of the front and rear chassis. There is one fitting for the front brakeand one fitting for the rear brake.


Hydraulic oil, under pressure from the Brake Treadle Valve, is applied to thepiston, forcing it to move. The movement of the piston compresses the frictionand metal brake disks together, creating the braking force needed by the machine.

Return springs force the piston to retract, which returns the oil from behind thepiston to the tank and provides clearance between the friction and metal disks.

Disassembly of the brake requires the removal of the planetary cover assemblyfirst. Special tools are required for the removal and reassembly of the brakes.


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BRAKES


621C, 721C, and 821C


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BRAKES


921C

General Description

The 921C are the only 21C Series machine using the GKN limited slip axles. Thissame axle has been used since the machines introduction.

Each of the four brake assemblies is mounted in the planetary assembly.

The brake pressure can be checked at the quick disconnect fitting. The quickdisconnect fittings are located on the right side of the unit near the pivotconnection of the front and rear chassis. There is one fitting for the front brakeand one fitting for the rear brake.


Hydraulic oil, under pressure from the Brake Treadle Valve, is applied to thepiston, forcing it to move. The movement of the piston compresses the frictionand metal brake disks together creating the braking force needed by the machine.Return springs force the piston to retract, returns the oil from behind the piston tothe tank, and allows clearance between the friction and metal disks.

Disassembly of the brake first requires the removal of the planetary coverassembly. Special tools are required for the removal and reassembly of thebrakes.


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BRAKES


921C

p02 C Brake Master

Documents

Transcript of p02 C Brake Master