Locking the Fifth Wheel Lock Mechanism
- Chock the front and rear of the trailer tires to prevent the trailer from moving.
- The fifth wheel jaw must be fully open. Make sure that the operating rod is in the unlocked position. The fifth wheel must be completely lubricated with chassis or multi-purpose grease. For lubrication instructions, see Group 31 of the Century Class Trucks Maintenance Manual.
- Make sure the fifth wheel top plate is tilted so the ramps are as low as possible. If equipped with an air suspension, make sure the air bags are completely inflated.
- Position the tractor so that the center of the fifth wheel
is in line with the trailer kingpin. The kingpin should be in a position
to enter the throat of the locking mechanism. See Fig.. Adjust the trailer landing gear so that the lower front
trailer edge contacts the top surface of the tilted fifth wheel plate,
approximately 8 inches (20 cm) before the fifth wheel center.
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Locked Position
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Jaw movement compresses spring.
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Fully open.
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Operating Lever
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Safety Latch
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Jaw
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Jaw Eccentric Pin
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Lock
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Spring
Fig. 1, ASF Castloc II and Simplex Series Kingpin Locking Mechanism Operation
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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 enters the throat of the locking mechanism. Continue backward motion until positive lockup occurs.
- Apply the tractor parking brakes.
- Make a visual check (even if equipped with the Touchloc
air-operated system) for positive kingpin lockup. The trailer bed
plate must be flush on the fifth wheel plate surface. When positive
lockup has occurred, the fifth wheel operating rod will have moved
inward to the locked position, and the safety latch will swing freely
over the operating rod. See Fig..
Fig. 2, Simplex Kingpin Locking Mechanism, Safety Latch (locked position)
- Release the tractor parking brakes. Test for kingpin lockup by pulling on the trailer against the chocks.
- 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 system lines.
- Charge the air brake system with air. Make sure that the air connections do not leak.
- With the trailer wheels chocked and the brakes set, check for clearance between the kingpin and the fifth wheel jaws by moving the tractor forward and backward against the locked kingpin. A clearance of approximately 1/16 inch (1.6 mm) between the jaw and kingpin is allowable. When clearance between the jaw and kingpin exceeds 1/8 inch (3 mm), adjust the jaw to restore the 1/16-inch (1.6-mm) clearance between the jaw and kingpin. For instructions, see Group 31 of the Century Class Trucks Workshop Manual.
- 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 ratings 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 pull handle, if so equipped, and the slide locking wedges 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 member 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.
Note: Only when the operating rod is fully retracted in the locked position will the safety latch be freely rotated down.
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.
Warning: Adjust the jaw pin if there is more than 1/8-inch (3-mm) clearance between the kingpin and the lock. Incorrect adjustment could cause the trailer to disconnect, possibly resulting in serious personal injury or death.