Inspecting Doubles and Triples
Inspecting Doubles and Triples
This domain tests a walk-around inspection of the whole combination, not just the tractor. You must show that you check the front trailer, the converter dolly, the rear trailer, and every connection between them.
Core rules
- Inspect from the tractor outward: tractor, front trailer, converter dolly, rear trailer. At each fifth wheel, check mounting bolts, jaws, locking latch, and release handle.
- On the converter dolly, check the frame, fifth wheel, pintle hook or lunette eye, safety chains, air lines, electrical cord, tires, wheels, rims, lights, and mud flaps.
- At the front trailer’s rear coupler, check the pintle hook, safety chains, glad hands, and the dolly drawbar. Confirm the chains are attached and not twisted.
- Check the rear trailer’s kingpin, apron, spring brakes, lights, tires, wheels, rims, and suspension. Confirm the rear trailer’s brake lights and turn signals work through the green cord.
- Check the emergency line breakaway: with the emergency line disconnected, the rear trailer’s spring brakes should apply. Reconnect and recharge before moving.
- Check line routing: no dragging, no chafing on the dolly frame or landing gear, enough slack for turns.
Worked example
The front trailer’s turn signals work, but the rear trailer’s do not. The tractor and front trailer are fine, so the fault is downstream: the green cord at the dolly, a corroded plug pin, or the rear trailer’s lamp. You check the dolly connection first because it is the newest connection and the most likely to be loose after coupling.
Traps
- Inspecting only the tractor and front trailer.
- Skipping the converter dolly because it is just a dolly.
- Not testing the rear trailer’s lights and brakes.
- Assuming the emergency line will set the brakes without checking.
- Missing chafed lines routed over a frame edge.