CDL Combination Vehicles TestCoupling and UncouplingEasy
A driver is preparing to uncouple a combination vehicle. After ensuring the landing gear is fully down and supporting the trailer, what is the next critical step before pulling the tractor forward?
- AEngage the trailer's emergency brakes manually.
- BRelease the tractor's parking brake.
- CDisconnect the air lines and electrical cable.
- DRaise the landing gear slightly to relieve pressure.
Show answer & explanationAnswer & explanation
Correct answer: C. Disconnect the air lines and electrical cable.
After ensuring the landing gear is supporting the trailer, the air lines and electrical cable must be disconnected to allow the tractor to move away freely. Failing to do so would damage these connections.
Why the other options are wrong
- A. The trailer's emergency brakes are already applied by the red glad hand; manual engagement is typically not a 'next critical step' here.
- B. Releasing the tractor's parking brake is done after all disconnections and the fifth wheel release.
- D. The landing gear should be firmly on the ground, not raised slightly, before disconnecting.
Air/Electrical Disconnection (Uncoupling)
The step in uncoupling where the air lines (service and emergency) and the electrical cable are physically separated from the trailer's connections.
- Performed after landing gear is down.
- Prevents damage to lines/cables.
- Ensures full separation capability.
Memory trick: Landing Gear Down, Then Lines Out!