Coupling and Uncoupling Multiple Trailers
Coupling and Uncoupling Multiple Trailers
This domain tests the order of operations and safety checks for building and breaking down a tractor–trailer–dolly–trailer combination. The examiner looks for a repeatable sequence, a tug test at every fifth wheel, and confirmation that air and electrical lines are routed without kinks or chafing.
Coupling sequence
- Spot the first trailer, chock wheels, and confirm the kingpin and fifth-wheel jaws are serviceable.
- Back the tractor under, listen for the click, perform a tug test, then visually confirm the jaws are closed around the kingpin.
- Connect the service and emergency air lines and the electrical cord; check for chafing.
- Raise the landing gear fully, then connect the converter dolly to the rear of the first trailer at the pintle hook, attaching safety chains and air lines.
- Back the second trailer onto the dolly fifth wheel, tug-test, and connect its lines.
Uncoupling sequence
Reverse the order: set brakes and chock wheels, disconnect lines, lower landing gear, release the fifth-wheel jaw, and pull forward slowly. For a dolly, close the pintle latch and stow the dolly securely.
Worked example
A driver couples a dolly but forgets the safety chains. The air lines hold during a straight pull, but on a tight turn the pintle opens and the dolly separates. The chains are a secondary retention device; without them the combination is illegal and unsafe. The correct fix is to attach chains crossed under the drawbar before the tug test.
Traps
- Skipping the tug test after the second trailer.
- Leaving the dolly's spring brakes released before the lines are connected.
- Pulling forward before landing gear is fully raised.
- Assuming a visual check alone proves jaw lock; the tug test is the proof.