Locking the Fifth Wheel Mechanism
- Chock the front and rear of the trailer tires to prevent the trailer from moving.
- The kingpin lock mechanism must be fully open, and the fifth wheel plate must be completely lubricated with chassis grease. For lubrication instructions, see of the Century Class Trucks Maintenance Manual.
- Position the tractor so that the fifth wheel lock opening
is in line (both vertically and horizontally) with the trailer kingpin.
The kingpin should be in a position to enter the throat of the locking
mechanism, to prevent a false lockup. See Fig.. Adjust the trailer landing gear to give enough alignment height
so that the fifth wheel picks up the trailer on the fifth wheel ramps.
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Locks open.
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Locks closed.
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Kingpin correctly entering the lock. Note how the depressed tongue allows lock halves to close completely around the neck and shoulder of the kingpin.
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Kingpin incorrectly entering the lock. Note how the steel tongue prevents lock halves from closing, preventing false lockup.
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Fifth Wheel Plate
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Trailer
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Kingpin
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Lockguard
Fig. 1, Lockguard Mechanism (rear view)
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- With the fifth wheel lock opening aligned with the trailer kingpin, back the tractor slowly toward the trailer, making sure that the kingpin correctly enters the throat of the locking mechanism. When the trailer is picked up by the fifth wheel, stop the tractor, then continue slow backward motion until positive lockup occurs.
- Apply the tractor parking brakes.
- Make a visual check for proper kingpin lockup. Release the tractor parking brakes. Test for kingpin lockup by pulling on the trailer against the chocks. Check for correct maximum clearance between the lock halves. If more than 1/8-inch (3.2-mm) clearance exists between the lock halves, the lock must be adjusted. See Group 31 of the Century Class Trucks Workshop Manual for adjustment procedures.
- After lockup is completed, connect the tractor-to-trailer air system lines and electrical cable to the trailer. Take care to prevent dirt or foreign material from entering the air lines.
- Charge the air brake system with air. Make sure that the air connections do not leak.
- Retract the trailer landing gear and secure the ratchet handle.
- Remove the chocks from the trailer tires.
- The load distribution on the front steering axle and rear
drive axle(s) will have a direct effect on the steering control of
the vehicle.
Determine the front and rear axle weights by weighing the vehicle on scales designed for this purpose.
The maximum axle weight ratings are shown on the Federal Motor Vehicle Safety Standard (FMVSS) label or Canadian Motor Vehicle Safety Standard (CMVSS) label attached to the left rear door post of the tractor. The desired load on the axle is no less than 80 percent of the maximum axle weight rating, but in no instances should the axle load exceed the maximum axle weight rating given on the FMVSS or CMVSS label.
Warning: Do not overload any tractor axle by improperly loading the trailer. This could cause erratic steering and loss of vehicle control, possibly resulting in serious personal injury or death.
Notice: Before attempting to lock or unlock the fifth wheel lock mechanism of a sliding type fifth wheel, the slide release plungers must be in the locked position. This prevents the sliding member from moving rapidly to the far forward or rearward position, which could damage the fifth wheel or kingpin.
Warning: Keep the fifth wheel plate lubricated to prevent binding between the tractor and trailer. A binding fifth wheel could cause erratic steering and loss of vehicle control, possibly resulting in serious personal injury or death.
Warning: Adjust the locks correctly to a maximum clearance of 1/8 inch (3 mm). Incorrect adjustment of the lock could cause the trailer to disconnect, possibly resulting in serious personal injury or death.
Notice: Always make sure the connect-hanger/support keeps the trailer air hoses and electrical cables positioned so that they do not rub on anything. Rubbing may wear through hoses or cables, resulting in air leaks, or exposed or broken wires, potentially affecting trailer brake or electrical systems.