CDL Combination Vehicles TestCoupling and UncouplingHard
A driver is preparing to back under a trailer. What is the correct position for the fifth wheel to ensure safe coupling?
- ATilted down towards the rear of the tractor with the jaws open.
- BTilted fully backward with the jaws closed and locked.
- CFlat against the tractor frame with the jaws open.
- DTilted fully forward with the release handle pulled out.
Show answer & explanationAnswer & explanation
Correct answer: A. Tilted down towards the rear of the tractor with the jaws open.
For safe and proper coupling, the fifth wheel should be tilted down towards the rear of the tractor. This allows the trailer's apron plate to slide up onto the fifth wheel, guiding the kingpin into the open jaws. The jaws must be open, meaning the release handle should be pulled out, to accept the kingpin.
Why the other options are wrong
- B. Jaws must be open to receive the kingpin; if closed and locked, coupling cannot occur.
- C. While the jaws should be open, the fifth wheel should be tilted, not flat, to aid coupling.
- D. A fully forward tilt would prevent the trailer from sliding onto the fifth wheel.
Fifth Wheel Tilt Position
The angle of the fifth wheel plate, typically tilted down towards the rear, to facilitate the entry of the trailer's kingpin during coupling.
- Aids smooth coupling.
- Prevents damage to components.
- Requires jaws to be open.
Memory trick: Tilt it down, jaws apart, ready for the start.