Fifth Wheels

Fifth Wheels, General Information

Do not use any fifth wheel that fails to operate properly. Doing so may cause loss of vehicle control, possibly resulting in severe personal injury or death.

Air-Suspension Dump Valve

The air-suspension dump valve may be used to adjust the tractor height to aid with coupling to or uncoupling from a trailer. See Fig. 17.1 . When the switch is set to LOWER, the air-suspension dump valve deflates the air springs to lower the rear of the vehicle. In the AUTO position, the automatic ride-control valves operate for normal driving.

Never exhaust air from the suspension while driving. The suspension will not absorb road shocks, possibly damaging components, and vehicle handling may be compromised. This could result in loss of vehicle control, possibly resulting in severe personal injury or death.

NOTICE

Do not operate the vehicle over uneven ground such as ramps, speed bumps, curbs, etc. with the air springs deflated. Doing this may lead to air bag separation from the piston, preventing the suspension air springs from inflating.

Fig. 17.1, Air-Suspension Dump Valve

Fifth Wheel Lubrication

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 personal injury or death.

The standard fifth wheel plate must be kept well lubricated with chassis grease to prevent friction and binding between the tractor fifth wheel plate and the trailer.

For a low-lube fifth wheel plate, inspect the condition of the low-lube pads. There should be no damaged or missing pieces. Slight puckering at the outside edges is normal.

For lubrication instructions, see Group 31 of the Argosy Maintenance Manual .

Fifth Wheel Coupling

Fifth wheel coupling is activated with the release handle located on either the right side or left side of the fifth wheel. Coupling has successfully occurred when the kingpin has been forced into the jaws and the release handle has moved to the locked position.

NOTICE

Some fifth wheels may be mounted on sliding rails. Before attempting to couple a trailer to a sliding fifth wheel, the slide feature must be locked to prevent the top plate from sliding rapidly forward or rearward, causing damage to the fifth wheel or kingpin.

Coupling, Fontaine or Holland Fifth Wheel

Chock the trailer tires.

Ensure the fifth wheel jaw is fully open and the release handle is in the unlocked position.

Make sure the fifth wheel top plate is tilted so the ramps are as low as possible.

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.

NOTICE

Attempting to couple at the wrong height may cause improper coupling, which could result in damage to the fifth wheel or kingpin.

Adjust the trailer height if required.

For a standard fifth wheel plate , the trailer should contact the fifth wheel approximately 4 to 8 inches (10 to 20 cm) behind the fifth wheel pivot. See Fig. 17.2 .

For a low-lube fifth wheel plate , the fifth wheel must slide freely under the trailer, and the trailer should contact the fifth wheel at the pivot. See Fig. 17.3 .

A. Fifth wheel must lift trailer
B. Adjust trailer height
C. Ramps tilted down
D. 4 to 8 inches

Fig. 17.2, Trailer Connection Point, Standard Fifth Wheel

A. Adjust trailer height
B. Ramps tilted down

Fig. 17.3, Trailer Connection Point, Low-Lube Fifth Wheel

With the fifth wheel lock opening aligned with the trailer kingpin, back the tractor slowly toward the trailer. After sliding under the trailer, STOP to prevent from hitting the kingpin too hard, then resume backing slowly until the fifth wheel locks.

On a standard fifth wheel, the fifth wheel must lift the trailer.

On a low-lube fifth wheel, do not lift the trailer as this may damage the fifth wheel plate.

Apply the tractor parking brakes.

A visual inspection is required by law. Some improper couplings can pass a pull test. Sound is not reliable. Get out of the cab and look. Incorrect coupling could cause the trailer to disconnect, possibly resulting in serious personal injury or death.

Perform a coupling inspection, checking that there is no gap between the bottom of the trailer and the fifth wheel, and that the kingpin is securely locked. See Fig. 17.4 .

When the kingpin is locked securely, the fifth wheel release handle moves to the locked position. Make sure that the safety latch is down over the release handle to hold the release handle in the locked position (the safety latch will only rotate down if the control handle is fully retracted in the locked position).

A. No gap between trailer and fifth wheel
B. Kingpin inside lock

Fig. 17.4, Coupling Inspection

Release the tractor parking brakes. Test for kingpin lock slowly inching the tractor forward, pulling on the trailer against the chocks.

10.

After kingpin lock is completed, connect the tractor-to-trailer air system lines and the electrical cable to the trailer. Take care to prevent dirt or foreign material from entering the air system lines.

NOTICE

Always make sure the connection hanger 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.

11.

Charge the air brake system with air, checking that the air connections do not leak.

Incorrect fifth wheel lock adjustment could cause the trailer to disconnect, possibly resulting in serious personal injury or death.

12.

With the trailer tires 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. If slack is present, uncouple the trailer and have the fifth wheel inspected and adjusted by a certified technician.

Coupling, Jost Fifth Wheel

Tilt the ramp down.

Open the kingpin locks. See Fig. 17.5 .

A. Lock held open by catch mechanism

Fig. 17.5, Jost Release Handle Unlocked

Back the vehicle close to the trailer, centering the kingpin on the fifth wheel.

Chock the trailer tires.

Connect the air lines and electrical cable.

Ensure that the red trailer air supply valve (trailer brake) is pulled out, and that the trailer parking brakes are set. See Chapter 5 in this manual for operation of the dash-mounted brake controls.

NOTICE

Attempting to couple at the wrong height may cause improper coupling, which could result in damage to the fifth wheel or kingpin.

Adjust the trailer height (if required).

For a standard fifth wheel plate , the trailer should contact the fifth wheel approximately 4 to 8 inches (10 to 20 cm) behind the pivot. See Fig. 17.2 .

For a low-lube fifth wheel plate , the fifth wheel must slide freely under the trailer, and the trailer should contact the fifth wheel at the pivot. See Fig. 17.3 .

Back the tractor under the trailer.

On a standard fifth wheel, the fifth wheel must lift the trailer.

On a low-lube fifth wheel, do not lift the trailer as this may damage the fifth wheel plate.

After sliding under the trailer, STOP to prevent from hitting the kingpin too hard, then resume backing slowly until the fifth wheel locks.

10.

Apply the tractor parking brake, then perform a physical check for positive kingpin lock, and that there is no gap between the trailer and the fifth wheel. See Fig. 17.4 .

11.

Ensure that the release handle is in the locked position adjacent to the casting. See Fig. 17.6 .

Fig. 17.6, Jost Release Handle Locked

12.

Release the tractor parking brakes and test for kingpin lock by slowly moving the tractor forward, pulling on the trailer against the chocks.

Fifth Wheel Uncoupling

Manual Uncoupling

Apply the tractor and trailer parking brakes.

Chock the trailer tires.

Lower the trailer landing gear until the weight is removed from the fifth wheel.

Disconnect the tractor-to-trailer air system lines and electrical cable. Plug the air lines to prevent dirt or foreign material from entering the lines.

Verify that both the yellow parking-brake and red trailer-air-supply knobs are out, the tractor and trailer parking brakes are set, and that the trailer is prepared for uncoupling.

Release the kingpin locking mechanism following the instructions for each manufacturer below.

6.1

Fontaine: Lift the safety latch and pull the lock release handle to the unlocked position.

6.2

Holland: In the locked position the safety indicator swings freely over the release handle.

6.2

Pull the release handle out. When the upper release handle shoulder is outside the slot, raise the handle and place the shoulder of the upper rod against the plate casting, above the slot.

6.2

The fifth wheel is now in the lock position and is ready for uncoupling. As the tractor pulls away from the trailer the kingpin forces the jaw to rotate, contacting the lock. Continued rotation of the jaw forces the lock to move outward, and drops the upper rod back into the slot. The wheel is now ready for coupling.

6.3

Jost: Pull the retractable release handle out, then secure it in the open position with the catch. See Fig. 17.5 .

Release the tractor parking brake then drive out slowly, allowing the trailer to slide down the fifth wheel and pick-up ramps.

Air-Actuated Uncoupling

An air-actuated kingpin release valve is optional with any fifth wheel. See Fig. 17.7 .

Fig. 17.7, Air-Actuated Kingpin Release Valve

NOTE: In the event of an air system failure, air-actuated kingpins can be manually released following the instructions for manual unlocking.

Once the kingpin release valve has been pulled the kingpin lock is released. The vehicle MUST NOT be driven with the trailer until the trailer has been uncoupled and coupled again. Failure to do so may result in separation of the trailer from the tractor, possibly causing serious personal injury or death.

Preparing the Trailer for Uncoupling

Before using the air valve to unlock a fifth wheel kingpin, prepare the trailer as follows.

Apply the tractor and trailer parking brakes.

Chock the trailer tires.

Lower the trailer landing gear until the weight is removed from the fifth wheel.

Disconnect the tractor-to-trailer air lines and electrical cable. Plug the air lines to prevent dirt or foreign material from entering the lines.

Air-Activated Kingpin Unlock, Fontaine or Holland Fifth Wheel

Verify that both the yellow parking-brake and red trailer-air supply knobs are out, the tractor and trailer parking brakes are set, and that the trailer is prepared for uncoupling.

NOTE: With a Fontaine or Holland fifth wheel, if the tractor parking brake is not set, the air-actuated kingpin-release valve will not activate.

Pull and hold the kingpin release valve ( Fig. 17.7 ) until the kingpin lock mechanism opens and locks in place.

Release the kingpin release valve.

Release the tractor parking brake.

Drive out from under the trailer.

Air-Activated Kingpin Unlock, Jost Fifth Wheel

Verify that both the yellow parking-brake and red trailer-air-supply knobs are out, the tractor and trailer parking brakes are set, and that the trailer is prepared for uncoupling.

NOTE: With a Jost fifth wheel, if the trailer parking brake is not set the air-actuated valve will not activate.

Release the tractor parking brake.

Pull and hold the kingpin release valve until the kingpin lock mechanism opens and locks in place.

After the trailer has slid down the fifth wheel and pick-up ramps, release the kingpin release valve.

Fifth Wheel Slide

Adjust the fifth wheel slide correctly, and do not overload any tractor axle by incorrectly loading the trailer. Incorrect slide adjustment or improper axle loading could cause erratic steering and loss of vehicle control, possibly resulting in serious personal injury or death.

On sliding fifth wheel assemblies, the fifth-wheel plate is attached to rails that allow forward and rearward movement of the fifth wheel to optimally distribute the load across the axles. Slots are evenly spaced along the slide rails, and retractable wedges are positioned through the slots to hold the fifth wheel in the desired position.

The amount of 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.

Air Slide Operation

The slide feature may be operated with an air switch mounted in the dash, that operates an air cylinder that locks and unlocks the slide. See Fig. 17.8 .

1. Fifth Wheel Air-Slide Switch

Fig. 17.8, Air-Slide Switch

Set the air-slide switch ( Fig. 17.8 ) to UNLOCK.

Ensure the locking plungers have released. See Fig. 17.9 .

For a Jost fifth wheel, the mechanism activates as shown in Fig. 17.10 .

1. Locking Wedge
2. Air Cylinder

Fig. 17.9, Air-Operated Sliding Fifth Wheel (Fontaine shown)

A. Unlocked
B. Locked

Fig. 17.10, Sliding Fifth Wheel, Jost

Lower the trailer landing gear just enough to remove the weight from the tractor.

Pull the red trailer-air-supply knob to set the trailer-parking brakes.

Slowly move the tractor forward or backward until the fifth wheel is in the desired location.

NOTICE

Ensure the trailer landing gear does not come in contact with the tractor frame or other components, and that the front of the trailer will not come in contact with the rear of the cab or other components if they extend beyond the rear of the cab.

Apply the tractor parking brakes.

Check that the locking wedges have seated in the slots. Failure to achieve complete lockup may allow disengagement of the tractor from the trailer, possibly resulting in serious personal injury or death.

Set the air-slide switch to LOCK. Visually inspect the locking wedges or plungers to make sure that they are fully inserted in the slide rail slots. Verify that the plungers have engaged by tugging the tractor forward while the trailer brakes are locked and the tires are chocked.

NOTE: The fifth wheel may need to be moved slightly to enable the locking wedges to fully lock.