Coupling and Uncoupling
What this domain covers
Coupling and uncoupling questions test sequence, not just vocabulary. The examiner wants to see that you verify the fifth wheel, kingpin, air lines, electrical cord, landing gear, and trailer brakes in an order that prevents a dropped trailer.
Core rules
- Chock trailer wheels, set the trailer parking brake, and check that the trailer floor height matches the tractor's fifth wheel.
- Back slowly in a straight line; the kingpin should enter the throat and the jaws should close with a visible latch.
- Do a tug test: set the trailer brake, pull forward gently, and confirm the trailer resists. Then visually check the jaws are closed around the kingpin and the safety latch is in place.
- Connect the emergency (red) and service (blue) air lines, then the electrical cord. Keep the lines from crossing or dragging.
- Charge the trailer air system, release the trailer brake, and raise the landing gear fully. Check trailer lights and brakes before moving.
Worked example
You back under a trailer and hear the jaws close. You connect the lines, raise the gear, and pull out. The trailer drops. Why? No tug test and no visual check. The correct sequence is: back, listen and feel, tug with trailer brake set, visually confirm the latch, then connect lines and raise gear.
Traps that cost marks
Skipping the tug test; forgetting to set the trailer brake before the tug; raising landing gear before the air lines are connected; crossing red and blue lines; and leaving the trailer at the wrong height so the tractor strikes the kingpin plate.