Coupling and Uncoupling
What this domain tests
This domain tests the safe sequence for connecting and separating a tractor and trailer, including fifth-wheel inspection, kingpin engagement, air and electrical connections, landing gear and the tug test. The exam focuses on preventing dropped trailers and brake-line damage.
Core rules
- Before coupling, check the fifth wheel: jaws open, locking lever in place, mounting secure, no cracks, and the apron free of debris. Check the kingpin for wear and the trailer height so the kingpin will enter the throat, not ride over it.
- Back slowly and squarely. After the jaws close, perform a tug test: pull gently forward and confirm the trailer moves with the tractor and the coupling does not pull apart. Then inspect visually for a gap between the fifth wheel and trailer apron.
- Connect the service and emergency air lines in the correct glad hands, open the shut-off valves, and connect the electrical cord. Check trailer lights and brake operation.
- Raise the landing gear fully and secure the crank. Release the trailer parking brake only after the coupling and air connections are verified.
- To uncouple, park on firm level ground, set the tractor parking brake, chock trailer wheels if needed, lower the landing gear to the ground, disconnect the air lines and electrical cord, release the fifth wheel, and pull forward slowly.
- Never raise the landing gear before the tractor is securely coupled, and never disconnect the air lines before the trailer is supported and braked.
Worked example
A driver backs under a trailer, hears the fifth wheel click, connects the air lines and starts to raise the landing gear. A tug test then shows the trailer separating from the tractor. The cause is likely a high hook: the kingpin was above the fifth wheel and the jaws never closed. The driver must lower the trailer, pull forward, adjust trailer height, back under again, confirm jaw closure and repeat the tug test before raising the gear.
Traps
Skipping the tug test, trusting the click alone, raising the landing gear too early, and disconnecting air lines before setting trailer brakes are frequent mistakes. Also check that the locking lever is secured, not just that the jaws look closed.