Coupling and Uncoupling
Coupling and Uncoupling
This domain tests the sequence for connecting and separating a tractor and trailer safely. The exam focuses on fifth-wheel and kingpin checks, the tug test, air-line connection, landing gear, and wheel chocks.
Coupling sequence
- Inspect the fifth wheel: jaws open, mounting secure, plate lubricated. Inspect the trailer kingpin for wear or damage.
- Chock the trailer wheels. Back the tractor slowly and squarely so the kingpin enters the fifth wheel.
- After the jaws lock, perform a tug test with the trailer brakes set: pull gently in low gear. If the tractor moves and the trailer does not, the coupling is not secure.
- Visually check that the jaws are closed around the kingpin, the safety latch is engaged, and there is no gap between tractor and trailer.
- Connect the red and blue air lines, open the shut-off valves, charge the trailer, and check for leaks. Connect the electrical cord and test the lights.
- Raise the landing gear fully and secure the crank. Release the trailer brakes.
Uncoupling sequence
Park on firm ground, set the trailer brakes, and chock the wheels. Lower the landing gear until it bears the trailer weight. Disconnect the electrical cord and air lines, then release the fifth-wheel jaws and pull the tractor slowly forward.
Worked example
A driver backs until the fifth wheel clicks, connects the lines, raises the gear, and drives away. The trailer later separates because the jaws never closed around the kingpin. The missing step was the tug test and visual check.
Traps that cost marks
Backing too fast, skipping chocks, forgetting to raise the landing gear, and disconnecting air lines before setting trailer brakes are common failures.
Key points
- Chock wheels before coupling or uncoupling.
- Perform a tug test with trailer brakes set.
- Visually confirm jaws closed and safety latch engaged.
- Red and blue lines must be sealed and leak-free.
- Lower landing gear before uncoupling; raise it fully after coupling.