Combination Vehicle Inspection and Coupling/Uncoupling
Combination Vehicle Inspection and Coupling/Uncoupling
This domain tests the pre-trip inspection of the tractor-trailer connection and the exact order for safe coupling and uncoupling. The examiner looks for a systematic walk-around, correct fifth-wheel engagement, and proof that you verified the connection rather than assumed it.
Inspection priorities
Inspect the fifth wheel jaws, kingpin, mounting bolts, safety latch, and pivot pins for cracks or wear. Check that the trailer kingpin plate is greased and the trailer height is set so the tractor’s fifth wheel will contact the plate without striking the kingpin or the trailer frame. Air lines and the electrical cord must have intact seals, no cracks, and enough slack to turn without dragging. Landing gear must be fully raised, crank secured, and mud flaps and lights undamaged.
Coupling sequence
Chock the trailer wheels and set the trailer brakes. Back slowly with the tractor aligned; stop just before contact and recheck height and alignment. Continue backing until the fifth wheel locks; listen for the click, then do a tug test by pulling gently forward with the trailer brakes still set. Secure the tractor, connect the service and emergency air lines and the electrical cord, and check for leaks. Raise the landing gear fully. Release the trailer brakes and do a pull test with the trailer brakes applied to confirm the coupling holds.
Uncoupling
Park on firm, level ground, set the tractor parking brake, chock the trailer wheels, and lower the landing gear to the ground. Disconnect the air lines and electrical cord, release the fifth-wheel latch, and pull forward slowly.
Worked example
If the trailer is too high, the tractor may pass under and the fifth wheel can strike the kingpin or trailer frame; if too low, the tractor can hit the trailer. Set the trailer so the fifth wheel slides under the plate and the kingpin enters the throat.
Traps
Relying on the click without a tug test, failing to check that the jaws closed around the kingpin, crossing service and emergency lines, leaving landing gear partly down, and forgetting to set trailer brakes before coupling.