Pulling Doubles/Triples and Inspecting the Combination
This domain tests whether you inspect the combination as one vehicle rather than a tractor plus cargo. A fault anywhere behind the tractor still belongs to you.
What the combination inspection covers
- Coupling devices: fifth wheel jaws, locking pins, safety latches, and the dolly's tow bar or drawbar.
- The converter dolly itself: frame, eye or pintle connection, safety devices, its own brakes.
- Air lines and electrical cords between every unit, routed and secured so they clear the ground and the frame.
- The rear of the last trailer: lights, reflectors, mud flaps, splash guards.
- Tires and wheels on each unit, including the dolly.
- Brakes on every unit: pushrods, slack adjusters, no audible leaks.
- Cargo securement and weight distribution, since the rearmost trailer's load changes handling most.
In-service checks
Recheck coupling, lines, and load after the first few miles and at every stop. Rough pavement and tight turns pull on cords and couplers more than straight highway running does.
Worked example
Thirty miles out, the last trailer's marker lights are dead while the first trailer's lights work. Reasoning: the shared circuit from the tractor is fine, so the break is downstream - a chafed cord, a pulled plug, or a loose connection at the dolly. Inspect the connection at the dolly first, not the bulbs.
Traps that cost marks
Inspecting only the tractor; assuming the last trailer's lights work because the first trailer's do; forgetting the dolly has its own brake and light connections; missing mud flap or splash guard defects on the final trailer; ignoring a load shift in the rear unit because the tractor still steers normally.