Coupling and Uncoupling Doubles and Triples
Coupling, step by step
- Inspect the fifth wheel first: jaws open, plate greased, mounting bolts tight, kingpin and apron undamaged.
- Set the trailer spring brakes (or chock the wheels) and line up squarely.
- Back under slowly and steadily; the trailer lifts slightly as the jaws close.
- Tug test: with the trailer brakes set, pull gently forward in a low gear. If the combination moves, the jaws are not locked - stop and start over.
- Get out and check: release handle pushed in, jaws closed around the kingpin, no gap between the trailer apron and the fifth wheel, safety latch engaged.
- Connect the air lines and electrical cord, seat the couplers, and support the lines so they cannot drag. The emergency (blue) line must be connected to charge the trailer and release its spring brakes.
- Raise the landing gear fully and stow the crank handle.
- Build air pressure, check for leaks, and test trailer brakes and lights before moving.
Uncoupling
Park on firm, level ground. Set the parking brakes and chock the wheels. Lower the landing gear to the ground before releasing anything, so the trailer has support. Disconnect the air lines and cord and hang them up. Pull the fifth wheel release handle, then pull the tractor slowly forward and stop to confirm the trailer is stable.
Traps
Question writers love reversed order - "raise the landing gear, then connect the lines" or "pull the release handle, then lower the gear." Also common: what the tug test actually proves (that the jaws are locked, not that the air lines are right).
Rule of thumb
Couple: back, tug, check, connect, raise. Uncouple: gear down, lines off, handle out, pull away.