CDL Combination Vehicles TestCoupling and UncouplingMedium
When uncoupling a combination vehicle, after disconnecting the air and electrical lines, what is the next correct action to ensure safety and prevent damage?
- ARelease the tractor's parking brake.
- BEngage the trailer's emergency brakes.
- CDrive the tractor slowly forward to clear the trailer.
- DCrank the landing gear down until it firmly supports the trailer.
Show answer & explanationAnswer & explanation
Correct answer: D. Crank the landing gear down until it firmly supports the trailer.
After disconnecting the air and electrical lines, the landing gear must be cranked down until it firmly supports the trailer. This prevents the trailer from falling when the tractor is pulled away, which could cause significant damage or injury.
Why the other options are wrong
- A. Releasing the tractor's parking brake is done just before pulling away, after the trailer is supported.
- B. The trailer's emergency brakes should already be engaged from earlier steps in the uncoupling process to hold the trailer in place.
- C. Driving away prematurely without proper landing gear support will cause the trailer to drop.
Landing Gear Deployment
The process of lowering and stabilizing the trailer's landing gear to support its weight when uncoupled from the tractor.
- Critical for trailer stability.
- Prevents trailer from dropping.
- Done before moving the tractor away.
Memory trick: Air and Electric off, then Legs down, then Tractor away.