Combination Vehicle Inspection and Coupling/Uncoupling
New York's CDL Combination knowledge test checks whether you can inspect a tractor-trailer as a system and couple or uncouple it without relying on luck. The exam favors sequence questions: what must be true before the tractor moves, and what proves the fifth wheel is locked.
Pre-trip items that matter most
- Fifth wheel: jaws open before coupling, no cracks, mounting bolts tight, plate greased.
- Kingpin and apron: no bends, wear, or missing bolts.
- Landing gear: fully raised, crank secured, no damaged shoes.
- Air lines: red emergency/supply, blue service; glad hand seals present; electrical cord secure.
- Trailer brakes: spring brakes set with no air; pushrod travel and slack adjusters within limits.
Coupling sequence
- Chock trailer wheels, check trailer height so the tractor will not strike the landing gear, and open the fifth wheel jaws.
- Back slowly and squarely; stop before contact; back under until you hear the lock.
- Tug test: with trailer spring brakes applied, pull gently in low gear. The trailer must not move; a click or movement means the jaws are not locked.
- Visually check that the jaws are closed around the kingpin and the safety latch is over the handle.
- Connect red and blue lines and the electrical cord; test trailer brakes and lights; raise landing gear fully and secure the crank.
Uncoupling
Park on level ground, chock the trailer, lower the landing gear to the ground, disconnect the lines and cord, pull the fifth wheel release handle, then pull forward slowly and confirm the trailer stays put.
Worked example: A driver backs under, hears a click, and immediately raises the landing gear. The tractor later pulls out from under the trailer. Reasoning: the click only means the lock may have engaged; the missing tug test and visual check allowed an unlocked fifth wheel to pass. Correct order is tug test and visual check before raising gear or moving.
Traps
- Treating the click as proof of coupling.
- Raising landing gear before the tug test.
- Crossing red and blue lines.
- Forgetting to chock or check trailer brakes.