CDL General Knowledge TestCombination Vehicles (if applicable)Medium
When performing a pre-trip inspection on a combination vehicle, a driver finds that the fifth wheel locking jaws are not fully closed around the kingpin. What is the immediate action the driver should take?
- ARe-couple the tractor to the trailer.
- BLubricate the fifth wheel mechanism to improve closure.
- CAttempt to force the jaws closed with a pry bar.
- DProceed with the inspection, noting it for later adjustment.
Show answer & explanationAnswer & explanation
Correct answer: A. Re-couple the tractor to the trailer.
If the fifth wheel locking jaws are not fully closed around the kingpin, the trailer is not securely coupled. This is an extremely dangerous condition that could lead to the trailer detaching. The only safe action is to uncouple and then re-couple the tractor to ensure a proper connection.
Why the other options are wrong
- B. Lubrication is part of maintenance, but it won't fix an improperly coupled kingpin.
- C. Attempting to force the jaws can damage the mechanism and doesn't guarantee a safe lock.
- D. This is a critical safety defect and cannot be ignored or deferred.
Fifth Wheel Locking Jaws
The fifth wheel locking jaws must be fully closed and secured around the kingpin for a safe connection between the tractor and trailer.
- Prevents trailer detachment.
- Must be visually inspected after coupling.
- An open or partially closed jaw indicates an unsafe condition.
Memory trick: Open jaws mean a re-do, no half-measures.