Coupling and Uncoupling Twin Trailers
Coupling and Uncoupling Twin Trailers
The exam tests the order of operations and the checks that prove each connection is locked. With twin trailers you build the combination from the tractor forward: tractor to lead trailer, converter dolly to the lead trailer, then the second trailer to the dolly. You never couple the rear trailer first.
Coupling checks
- Fifth wheel jaws fully closed around the kingpin; tug test with the tractor in a low gear.
- Landing gear fully raised and crank handle secured.
- Air lines connected, glad hands sealed, electrical cord plugged; shut-off valves open between trailers.
- Converter dolly safety chains attached and crossed so the dolly cannot drop to the pavement.
- Dolly fifth wheel locked on the second trailer's kingpin; safety latch engaged.
Uncoupling
Reverse the order: drop the rear trailer first, then the dolly, then the lead trailer. Lower landing gear before releasing the fifth wheel, and never pull out from under a trailer with the landing gear still up.
Worked example
You must leave the rear trailer at a terminal. Lower its landing gear, disconnect its air lines and electrical cord, open the dolly fifth wheel, and pull the tractor and lead trailer forward slowly. Then uncouple the dolly from the lead trailer. Dropping the lead trailer first would leave the dolly and rear trailer unsupported.
Traps
Skipping the tug test, leaving shut-off valves closed (no air to the rear brakes), and forgetting that safety chains must be crossed. Also, lowering landing gear after releasing the fifth wheel instead of before.