CDL Combination Vehicles TestCoupling and UncouplingMedium
During the uncoupling process, after the landing gear is firmly on the ground, what action must be taken with the trailer's brakes before pulling the fifth wheel release handle?
- APump the tractor's brake pedal to build air pressure.
- BRelease the trailer's emergency brakes.
- CEnsure the trailer's emergency brakes are engaged.
- DApply the trailer's service brakes.
Show answer & explanationAnswer & explanation
Correct answer: C. Ensure the trailer's emergency brakes are engaged.
Before pulling the fifth wheel release handle, it is absolutely crucial to ensure that the trailer's emergency brakes are engaged. This prevents the trailer from rolling away freely once it is disconnected from the tractor, which could lead to a runaway trailer incident.
Why the other options are wrong
- A. Pumping the brake pedal builds air pressure for the service brakes, but the emergency brakes are the primary means of securing an uncoupled trailer.
- B. Releasing the emergency brakes would be extremely dangerous, allowing the trailer to roll.
- D. The service brakes are controlled by the foot pedal and are not typically used to hold a parked, uncoupled trailer.
Trailer Brake Engagement (Uncoupling)
The critical step of ensuring the trailer's emergency brakes are set and holding the trailer firmly before the tractor is disconnected.
- Prevents runaway trailer.
- Emergency brakes engage automatically on air loss.
- Must be verified before releasing fifth wheel.
Memory trick: Brakes firmly set, no trailer regrets.