CDL-10 Section 7 - Doubles and Triples
CDL-10 Section 7, Doubles and Triples, covers combination vehicles with two or three trailers, including the converter dolly. Questions focus on coupling, uncoupling, air and electrical connections, and the handling effects of multiple trailers.
Core rules
- Coupling: check the fifth wheel and kingpin, back under squarely, confirm the jaws lock, perform a tug test, connect air lines and electrical cord, and raise the landing gear.
- Converter dolly: secure the dolly to the lead trailer, connect safety chains, and make sure shut-off valves are open only on connected lines. Close unused valves.
- Air lines: connect glad hands correctly, listen for leaks, and check that trailer brakes release and apply.
- Uncoupling: chock wheels, lower landing gear, disconnect lines, and pull out slowly. Never leave a trailer without chocks or brakes.
- Driving: multi-trailer units off-track more, surge back and forth, and amplify lateral movement toward the rear. Steer smoothly, turn wide, brake early, and avoid sudden lane changes.
Worked example
A driver backs under a converter dolly but forgets the tug test. The jaws may look closed but not be locked. The correct sequence is to back under, check the jaws, tug against the brakes, then connect the air lines and electrical cord. Only after the dolly is secure should the landing gear be raised.
Traps
Do not rely on a visual check alone; do not leave shut-off valves open on unused lines; and do not treat a triple like a single trailer when turning or stopping. Rearward amplification means the last trailer swings wider and reacts more sharply.