CDL Combination Vehicles TestInspecting Combination VehiclesEasy
You are performing a pre-trip inspection on a combination vehicle. When checking the fifth wheel assembly, you observe that the locking jaws are not fully closed around the kingpin, and there is a visible gap. Which of the following is the most appropriate action?
- AProceed with the trip, but drive at a reduced speed to prevent decoupling.
- BApply more grease to the fifth wheel plate and re-attempt coupling.
- CAttempt to gently rock the trailer back and forth to force the jaws closed.
- DEnsure the kingpin is properly seated, then re-inspect the locking jaws for full closure.
Show answer & explanationAnswer & explanation
Correct answer: D. Ensure the kingpin is properly seated, then re-inspect the locking jaws for full closure.
A visible gap in the locking jaws indicates the kingpin is not securely coupled. The most appropriate action is to ensure proper seating and re-inspect, as an improperly coupled trailer is extremely dangerous.
Why the other options are wrong
- A. Driving with an unsecured trailer is extremely hazardous and illegal.
- B. Grease aids coupling but won't fix an improperly seated kingpin or partially closed jaws.
- C. Forcing the trailer could damage the kingpin or fifth wheel and is not a safe solution.
Fifth Wheel Coupling
The fifth wheel is a coupling device that connects a semi-trailer to a tractor. Proper coupling involves the kingpin locking securely into the fifth wheel jaws.
- Connects tractor to trailer.
- Kingpin must be fully engaged in locking jaws.
- Visual and tug test required for secure connection.
- Proper lubrication is important for operation.
Memory trick: Kingpin in, jaws tight, green light!