Inspecting Combination Vehicles
Inspecting Combination Vehicles
This domain tests the combination-vehicle pre-trip inspection. The exam expects you to check the tractor, the trailer, and the connection between them, not just the power unit.
What to inspect
- Coupling system: fifth-wheel jaws closed around the kingpin, safety latch engaged, mounting bolts tight, no gap between tractor and trailer.
- Air and electrical connections: glad-hand seals present, lines not cracked or chafed, shut-off valves open, electrical cord secure, lights working.
- Landing gear: fully raised, crank secured, no damaged legs or missing pins.
- Trailer structure and securement: frame, crossmembers, floor, doors, mud flaps, cargo tie-downs.
- Tires and wheels: proper inflation, tread depth, no cuts or bulges, lug nuts tight, rust streaks checked.
- Brakes: slack adjuster and pushrod travel, chamber condition, air leaks, trailer brake operation.
Worked example
During a pre-trip, a driver finds the blue service line chafed through the outer layer near the glad hand. Although the brakes still apply, the line can fail under pressure and cause a loss of trailer service brakes. The correct action is to place the vehicle out of service until the line is replaced.
Traps that cost marks
Inspecting only the tractor, missing the trailer brake test, failing to check the landing gear crank, and assuming a light works because the tractor lights work are common errors. Do not overlook the fifth-wheel mounting bolts or the kingpin.
Key points
- Inspect the coupling, air lines, electrical cord, and landing gear.
- Confirm fifth-wheel jaws and safety latch are secure.
- Check trailer brakes, lights, tires, and securement.
- Chafed or cracked air lines are out-of-service defects.
- A combination inspection must cover tractor, trailer, and connection.