Jost Fifth Wheel Coupling

P4 DM Ch21; CasGen5 DM Ch20

Fifth wheel coupling is activated with the lock control 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 lock control 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.

  1. Tilt the ramp down.
  2. Open the kingpin locks. See Fig..

    • When the kingpin locks are opened, they will be held open by the catch mechanism.

    Fig. 1, Jost Release Handle Unlocked

  3. Back the vehicle close to the trailer, centering the kingpin on the fifth wheel.
  4. Chock the trailer wheels.
  5. Connect the air lines and electrical cable.
  6. Ensure that the red trailer air supply valve (trailer brake) is pulled out, and that the trailer parking brakes are set. See Ignition Switch in this manual for operation of the dash-mounted brake controls.

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

  7. 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..

    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..

    A proper connection for a standard fifth wheel trailer is ensured by all of the following:

    • The fifth wheel is lifting the trailer.

    • The trailer height is adjusted with the crank.

    • The ramps are tilted down.

    • The trailer is connected 4 to 8 inches behind the fifth wheel pivot.

    Fig. 2, Trailer Connection Point, Standard Fifth Wheel

    A proper connection for a low-lube fifth wheel trailer is ensured by both of the following:

    • The trailer height is adjusted with the crank.

    • The ramps are tilted down.

    Fig. 3, Trailer Connection Point, Low-Lube Fifth Wheel

  8. 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.

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

    10. Warning: 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.

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

    A successful inspection of the trailer coupling requires both of the following:

    • There is no gap between the trailer and fifth wheel.

    • The kingpin is securely locked.

    Fig. 4, Coupling Inspection

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

    Fig. 5, Jost Release Handle Locked

  12. Release the tractor parking brakes and test for kingpin lockup by slowly moving the tractor forward, pulling on the trailer against the chocks.
Note:
Parent topic: Fifth Wheel Coupling
Document Number: 0000112046
Manual Publication Date: 2025-02-11
Topic Publication Date: 2025-03-07