Chapter 34 Fifth Wheels and Coupling Systems. Objectives (1 of 3) Describe the different types of...
-
Upload
tristin-iddings -
Category
Documents
-
view
253 -
download
3
Transcript of Chapter 34 Fifth Wheels and Coupling Systems. Objectives (1 of 3) Describe the different types of...
Chapter 34
Fifth Wheels and
Coupling Systems
Objectives (1 of 3)
• Describe the different types of fifth wheels used on tractors.
• Outline the operating principles of the Holland, Fontaine, and ConMet fifth wheels.
• Understand the importance of correctly locating the fifth wheel on the tractor.
• Describe the locking principles of each type of fifth wheel.
Objectives (2 of 3)
• Outline the procedure required to couple and uncouple a fifth wheel.
• Service the common types of fifth wheels.
• Describe the procedure required to overhaul a fifth wheel.
• Identify the overhaul procedure required of some common fifth wheels.
Objectives (3 of 3)
• Define high hitch and outline what is required to avoid it.
• Describe the operating principle of a pintle hook and draw bar.
• Outline the function of the kingpin and upper coupler assembly.
Semi-oscillating Fifth Wheel
Shop Talk
• Most truck and trailer coupling mechanisms are simple in design and operating principles.
• However, because of the extreme consequences of a trailer breakaway, care must be practiced when doing any work on coupling devices.
• Always consult OEM service literature and ask questions when you are unsure of a procedure.
Sliding Fifth Wheel
Compensating Fifth Wheel
Compensating Fifth Wheel
Elevating Fifth Wheel
Shop Talk
• The fifth wheel location on the tractor affects the bridge formula, that is, how the load is distributed over the tractor and the trailer axles.
• Double-check that the fifth wheel is correctly located when installing. – Incorrectly placed fifth wheels can result in
weight-over-axle infractions and severely imbalanced dynamic braking.
Caution
• Installing a jaw set into a fifth wheel is a simple, everyday shop procedure.
• However, because of the serious consequences that result from a fifth wheel separation, it is essential that you carefully observe the OEM service literature during assembly and testing.
• Double-check every step in the procedure. Test the operation of a completed fifth wheel rebuild by coupling and uncoupling a couple of times to a trailer.
A-Lock
B-Lock
Conmet (now Holland) 400
Fontaine No-Slack
Locking Mechanism Adjustment
Slide Mechanism Adjustment
Shop Talk
• Do not attempt to inspect a fifth wheel without removing the grease.
• The best way to do this is to first scrape off as much as possible, and then apply some solvent before hot pressure washing.
• Check the turntable plate, throat, and saddle/pivot assembly for cracks.
• Check the dynamic action of the locking mechanism and the secondary lock integrity.
• Check all the mounting fasteners and welds.
Caution
• Installation welding on fifth wheel assemblies should be performed by a qualified welder.
• Improper welding procedures can result in a trailer separation—the consequences of this can be fatal!
Caution
• The trailer must be stationary with its parking brakes applied to prevent damage to the tractor or trailer by uncontrolled sliding of the fifth wheel.
Shop Talk
• On a sliding model fifth wheel, after locating it in the desired position, visually inspect the locking plungers to be sure that they are properly engaged.
• Also, set the trailer brakes and rock the tractor fore and aft.
• Do not attempt to shift a sliding fifth wheel when a trailer is in motion!
Caution
• Proper adjustment of the sliding bracket locking plungers must be performed at installation and maintained at regular intervals by use of the adjusting bolts provided on both sides.
• Proper adjustment is required for proper operation and for proper load transfer and distribution.
Caution
• Rebuilding of fifth wheels is a common shop practice.
• Although it is a simple procedure, each type of fifth wheel uses distinct locking mechanisms.
• Always use the manufacturer procedure included in every rebuild kit. A fifth wheel failure can have fatal consequences!
Air Slide
Manual Slide
Caution
• Always consult the manufacturer for the correct procedure when welding kingpins to upper coupler assemblies.
• Welding diagrams often are provided with replacement kingpins.
Pintle Hook
Drawbar
Summary (1 of 5)
• The purposes of the fifth wheel are both to permit the truck/tractor to articulate around the trailer kingpin when turning corners and to support a percentage of the weight of a semi-trailer.
• The semi-oscillating fifth wheel is the most common highway tractor fifth wheel.
• A semi-oscillating fifth wheel articulates or oscillates about an axis perpendicular to the vehicle centerline: that is, on a fore-aft plane.
Summary (2 of 5)
• Compensating fifth wheels are designed to provide both front-to-rear and side-to-side oscillation between the tractor and semi-trailer. – Side-to-side oscillation occurs below the fifth wheel
plate surface and lessens the effect of trailer torque or twist acting on the frame of the tractor or lead trailer.
• Fully-oscillating fifth wheels articulate on all planes and are used with gooseneck, low-bed trailers, especially those operated on rough, off-highway terrain.
• Elevating fifth wheels are used on yard shunt tractors. They may be equipped with either air or hydraulic lift mechanisms.
Summary (3 of 5)
• Many fifth wheels are built with a sliding mechanism that permits longitudinal adjustment placement of the fifth wheel on the tractor frame. – This allows the point at which the weight of the trailer
is supported by the tractor to be altered according to load and legislative requirements.
• Relocation of a sliding fifth wheel alters the weight-over-axle distribution on a tractor when coupled to a trailer. – As a fifth wheel is moved forward, the percentage of
weight carried by the tractor steer axle increases.
Summary (4 of 5)
• Fifth wheel mountings may be plate-mounted or angle-on-frame mounted.
• The fifth wheel should be inspected every 30,000 miles or 3 months, whichever comes first.
• Proper lubrication of the fifth wheel includes keeping a water-resistant, lithium-based grease applied to the fifth wheel plate, lubricating all moving parts with a light oil, and applying chassis grease to the grease zerks at the pivot points and the cam.
Summary (5 of 5)
• Kingpins are usually welded to the trailer upper coupler unit and are used to couple a trailer to the fifth wheel.
• Kingpins come in two SAE standard sizes, 2- inch and 3.5-inch. – They are manufactured in special alloy steels and
usually are welded to the upper coupler assembly. Bolted and removable kingpins also are used.
• A pintle hook and drawbar assembly is used to couple a full trailer to a truck or lead trailer.