Coupling and Uncoupling Procedures
Coupling and Uncoupling Procedures
The coupling and uncoupling domain tests a sequence: secure the trailer, align the tractor, back under, lock the fifth wheel, connect lines, test, and raise the gear. Uncoupling reverses it safely. Exam questions often turn on order and on the checks that prove the connection is real.
Coupling sequence
- Chock the trailer wheels and check the trailer parking brake.
- Inspect the fifth wheel: jaws open, safety latch released, mounting secure, grease present.
- Align the tractor squarely and back slowly; stop when the fifth wheel contacts the trailer apron.
- Listen for the jaws to close, then pull forward gently in a low gear: the tug test.
- Visually check that the jaws are closed around the kingpin and the safety latch is engaged.
- Connect the emergency and service lines, then the electrical cord. Check for chafing and secure the lines.
- Charge the trailer, test trailer brakes, raise the landing gear, and remove the chocks.
Uncoupling sequence
Park on level ground, apply the parking brake, chock the wheels, lower the landing gear to firm contact, disconnect the electrical cord and air lines, release the fifth-wheel jaws, and pull forward slowly. Do not leave the trailer on the landing gear alone.
Worked example
A driver backs under a trailer, hears the jaws close, connects the lines, and drives away. At the first bump the trailer separates. The missing step was the tug test and the visual check. Hearing a click is not proof: the jaws may have closed on the apron, not the kingpin. A pull test with the trailer brakes set, plus a look at the jaws from under the trailer, would have exposed a high hook.
Traps
- Skipping the tug test.
- Leaving the safety latch open.
- Connecting lines before the fifth wheel is locked.
- Raising the landing gear before the trailer is charged.
- Forgetting to chock wheels on a slope.
Key points
- Secure, align, back, lock, test, connect.
- Tug test and visual check are mandatory.
- Lines before gear-up; gear down before pull-out.
- Chock wheels whenever the trailer is unattended.
- A high hook is a separation waiting to happen.