Vehicle Inspection and Coupling/Uncoupling
Why the Walk-Around Matters
A combination vehicle fails at the weakest link, and the weakest link is usually a coupling or a connection. Before every trip, and after any long stop, you must inspect the tractor, the trailer, and every point where they meet. The core concepts: the fifth wheel and kingpin, the locking jaws, the safety latch or release handle in its locked position, the air and electrical lines, the landing gear, and the trailer frame and suspension.
Coupling Sequence
Back under the trailer squarely and slowly, with the trailer brakes set and the tractor lined up straight. After the tractor stops against the kingpin, pull forward gently in low gear to test that the jaws have closed and locked. Then tug-test with the tractor brakes released only after confirming the latch is down. Connect the air lines (emergency/red to emergency/supply, service/blue to service), then the electrical cord, then raise the landing gear fully and secure the crank handle.
Uncoupling Sequence
Park on firm, level ground, set the trailer spring brakes, lower the landing gear to the ground, and only then release the fifth-wheel latch and pull out slowly. Traps in questions: which line is red versus blue, whether the trailer brakes must be set before pulling the pin, and whether the landing gear should touch the ground before or after the tractor is released. Another common trap is confusing the tug test with the visual check of the jaws.
Rule of Thumb
"Set, lower, tug, connect, raise, check." If any single step is skipped, treat the vehicle as unroadworthy until re-verified.