CDL Combination Vehicles TestInspecting Combination VehiclesEasy
When inspecting the coupling of a combination vehicle, a driver notices that the fifth wheel locking jaws are open. What is the immediate safety concern?
- AImproper lubrication of the fifth wheel plate.
- BReduced air pressure to the trailer brakes.
- CPotential for trailer uncoupling during operation.
- DExcessive wear on the kingpin.
Show answer & explanationAnswer & explanation
Correct answer: C. Potential for trailer uncoupling during operation.
If the fifth wheel locking jaws are open, it means the kingpin is not securely held in place. This creates a critical safety hazard where the trailer could detach from the tractor while driving, leading to a severe accident.
Why the other options are wrong
- A. Improper lubrication is a maintenance issue that can cause wear, but open jaws mean the connection is already compromised.
- B. Fifth wheel locking jaws are mechanical and do not directly affect the air pressure to trailer brakes.
- D. While kingpin wear is a concern, open locking jaws are a more immediate and direct threat to coupling integrity.
Fifth Wheel Locking Jaws
The mechanism within the fifth wheel that closes around the trailer's kingpin to securely couple the trailer to the tractor.
- Must be fully closed and locked for safe operation.
- Open jaws indicate an unsecured coupling.
- Failure to lock can lead to trailer detachment.
Memory trick: Jaws must bite, or the trailer takes flight!