Pennsylvania CDL Combination cheat sheet

Combination Vehicles: Coupling, Inspection, and Control

• Fifth-wheel jaw check: after coupling, pull the tractor gently forward against the closed trailer brakes; a locked jaw holds, a high or open jaw lets the trailer move and the gap open.

• Tug test plus visual check: get under and confirm the fifth-wheel jaws are closed around the kingpin shank, the release lever is in the locked position, and no gap shows between apron and fifth wheel.

• Landing gear sequence: raise the gear fully before moving; crank it to the ground before uncoupling; after uncoupling, the trailer must rest on the gear, not on the tractor frame.

• Air line routing: connect the emergency (supply) line first and the service line second - the emergency line charges the trailer reservoir and charges faster; the service line only signals brake application.

• Trailer air protection valve: if the emergency line separates, the trailer brakes apply and stay applied (spring brakes), so a broken supply line leaves the trailer braked rather than free-rolling.

• Tractor protection valve: a closed tractor protection valve seals the tractor's air supply when the lines separate, letting the tractor keep enough pressure to stop; the red trailer air supply knob pops out.

• Off-tracking rule: the rear wheels of a tractor-trailer follow a shorter path than the front wheels, so swing wide before turns and watch the trailer's inside rear wheel, not the tractor's.

• Brake test before driving: with a fully charged system, release the parking brake, apply the foot brake and hold - if air pressure drops more than about 3 psi in one minute (single vehicle) or 4 psi (combination), there is a leak to fix.

• Stopping distance grows with weight and speed: a combination vehicle needs much more room than a car, and the heavier the load, the longer it takes to stop, so increase following distance as weight rises.