Inspecting Combination Vehicles
Inspecting Combination Vehicles
This domain tests the pre-trip inspection with the combination-specific items single-unit drivers never check. The exam expects a systematic order and a reason for each item.
The coupling area (most-tested)
- Fifth wheel: mounted securely, jaws closed, locking lever secured, plate greased.
- Kingpin and apron: no bends, cracks, or missing bolts.
- Air and electrical lines: no cuts, cracks, or worn spots; glad hand seals present; lines not crossed (blue emergency, red service).
- Landing gear: fully raised, crank handle secured, no missing parts.
Trailer and rear of combination
- Frame, crossmembers, and floor; doors and seals; cargo secured and not overloaded.
- Tires: tread depth, sidewall damage, proper dual spacing, no foreign objects.
- Wheels and rims: cracks, missing lugs, rust streaks.
- Suspension: broken leaves, loose or missing spring hangers, leaking air bags.
- Brakes: cracked drums, loose chambers, pushrod travel within limits, no audible air leaks.
- Lights and reflectors, mud flaps, and the trailer ABS light.
Procedure
Start at the same point every time and work around the vehicle in the same direction so nothing is skipped. With the engine running, apply the brakes and listen for leaks at the chambers and lines. Check the coupling both visually and with the tug test.
Worked example. During a walk-around you find a glad hand seal missing on the emergency line. Without the seal, the trailer will not build or hold pressure, and the trailer spring brakes may not release. That is a reason to reject the vehicle, not a note for later - a combination with an air leak in the supply line is not roadworthy.
Traps that cost marks. Checking tires and lights but skipping fifth wheel and kingpin; inspecting only one side; assuming a trailer coupled yesterday is coupled today; missing the trailer ABS light; inspecting in the dark without a flashlight.