Inspecting Combination Vehicles
Inspecting Combination Vehicles tests whether you can find the defects that actually take a combination out of service: coupling, air lines, brakes, tires, lights, and the trailer's running gear.
What to check and why
- Coupling system: jaws, kingpin, safety latch, mounting bolts, grease. A worn or unlatched fifth wheel drops trailers.
- Air lines and electrical cord: cuts, chafing, weather cracks, seals in the gladhands. Route the cord and lines so they cannot rub or be pinched on turns.
- Landing gear: fully raised, crank handle secured, legs straight.
- Trailer structure: frame cracks, sliding tandem locking pins fully seated, mud flaps, rear impact guard.
- Tires: at least 4/32 inch tread on steer tires and 2/32 inch elsewhere; no cuts, bulges, or exposed cord; duals matched and not touching.
- Brakes: slack adjusters, pushrod travel, hoses, chambers, drums; ABS lamp behavior.
- Lights: headlights high and low, clearance and marker lamps, turn signals, four-ways, brake, tail, plate light, reflectors - confirmed working at the trailer, not just at the switch.
- Cargo: securement, weight distribution, and nothing blocking lights or the plate.
The brake tests
Do the static leak test (3 psi single / 4 psi combination per minute, released and applied), confirm the low-pressure warning before 60 psi, check that the spring brakes set and release, and test the tractor protection valve and trailer emergency brakes by pulling the red knob and confirming the trailer brakes apply.
Worked example
During a walk-around, a driver finds the blue service line's outer jacket scuffed through to the reinforcement and one sliding-tandem locking pin only half engaged. Both are defects, not cosmetic issues. The line can burst under a hard application and leave the trailer without service brakes; the half-seated pin can let the tandem shift under load, changing axle weights and possibly dropping the trailer. The correct answer is that the unit does not dispatch until both are corrected.
Traps
- Inspecting the tractor thoroughly and waving at the trailer.
- Checking that the lights are on rather than that each individual lamp works.
- Skipping the brakes-applied leak test.
- Calling an ABS lamp that comes on at key-on a defect; it should go out after the self-test.