Tractor-Trailer Coupling, Uncoupling, and Tiller Operation
Tractor-Trailer Coupling, Uncoupling, and Tiller Operation
This domain tests the mechanical handshake between tractor and trailer and the technique of steering the trailer once they are joined. The exam favors sequence questions: what happens first, and what proves the step actually worked.
Coupling sequence
- Chock the trailer wheels. Check the kingpin and fifth-wheel plate for damage and lubrication.
- Back the tractor squarely; the fifth wheel should contact the trailer slightly below the kingpin so the jaws ride up and lock.
- After the jaws close, check the release handle is in the locked position and the safety latch is engaged.
- Pull test: set the trailer spring brakes and pull gently against them in low gear. If the trailer holds and the tractor will not move away, the coupling is sound.
- Connect the air lines to the correct glad hands, connect the electrical cord, test trailer lights and brakes, then raise the landing gear fully and secure the crank.
Uncoupling sequence
Chock, lower the landing gear to take the weight, disconnect and stow the lines in their dummy couplers, release the fifth-wheel handle, then pull forward slowly and stop.
Worked example
The pull test that fails. You set the trailer brakes and the trailer slides forward with the tractor while the landing gear is still on the ground. Reasoning: a locked kingpin holds the trailer against its own set brakes; if both move, the jaws are not around the pin - a high hook. Shut down, re-chock, inspect, and re-couple rather than driving with an unproven connection.
Tiller technique
Steering response varies between builders, so verify on your own rig in the drill yard whether wheel rotation moves the bogie left or right; do not import car-steering logic. Corrections are small at speed and larger at walking pace, and the trailer rear swings opposite the direction of the turn.
Traps
Skipping the pull test; forgetting to lower the landing gear before uncoupling; leaving the electrical cord in the dummy coupler for the next shift.