CDL General Knowledge TestCombination Vehicles (if applicable)Medium
During the uncoupling process, after you have lowered the landing gear and disconnected the air lines and electrical cable, what is the next step before pulling the tractor forward?
- AVisually check that the trailer's parking brakes are applied.
- BCompletely retract the landing gear.
- CRemove the kingpin from the fifth wheel.
- DRelease the tractor's parking brakes.
Show answer & explanationAnswer & explanation
Correct answer: A. Visually check that the trailer's parking brakes are applied.
After lowering the landing gear and disconnecting the lines, it's crucial to ensure the trailer parking brakes are set. If they are not, the trailer could roll away when the tractor is pulled forward. The trailer's parking brakes are typically applied automatically when the air lines are disconnected.
Why the other options are wrong
- B. Retracting the landing gear would cause the trailer to fall if it's not supported by the tractor.
- C. The kingpin is released by pulling the fifth wheel release handle, which happens after checking the trailer brakes and before pulling away.
- D. Releasing the tractor's parking brakes is done just prior to pulling away, but after confirming the trailer is secure.
Uncoupling: Trailer Brake Check
Verifying that the trailer's parking brakes are set and holding the trailer stationary before moving the tractor away.
- Prevents trailer runaway.
- Usually automatic when air lines are disconnected.
- Must be visually confirmed.
Memory trick: Park, Lower, Disconnect, Check, Pull, Clear.