Coupling and Uncoupling Procedures
What the exam checks
This domain tests the sequence for connecting and separating a tractor, converter dolly, and trailers without rolling, dropping, or damaging equipment. The examiner looks for chocks, brakes, landing gear, lines, and a final tug test.
Core rules
For coupling, secure the trailer being left, position the dolly squarely, back under or connect the pintle eye, and confirm the latch. Connect the emergency and service lines and electrical cord, raise the landing gear fully, and pull-test against set trailer brakes. For uncoupling, park on firm level ground, set the parking brakes, chock wheels, lower the landing gear until it bears weight, then disconnect lines and electrical cord. Release the fifth wheel only after the trailer is supported. With a dolly, lower the second trailer's landing gear, disconnect its lines, release the dolly fifth wheel, then secure and store the dolly. Never leave a trailer on the kingpin without support.
Worked example
A driver lowers the landing gear just enough to touch the ground, then releases the fifth wheel. The trailer may sink or tip because the gear is not carrying weight. The correct reasoning is to crank the gear down until it is firmly loaded, check that the trailer is stable, and only then pull the release handle. A tug test before departure confirms the coupling, but it does not substitute for proper landing gear support during uncoupling.
Traps that cost marks
Do not uncouple on a slope without chocks. Do not disconnect air lines before setting trailer brakes. Do not forget to raise and secure the dolly landing gear or crank handle. Do not pull away with the electrical cord still connected.