CDL Combination Vehicles TestCoupling and UncouplingHard
A driver is performing a pre-trip inspection of their combination vehicle. They notice that the fifth wheel release arm is not fully seated in its locked position, despite the kingpin appearing to be coupled. What is the most likely consequence if the driver proceeds without correcting this issue?
- AThe trailer's air brakes will not function correctly.
- BThe landing gear will not be able to fully retract.
- CThe kingpin could separate from the fifth wheel during operation.
- DThe electrical connection to the trailer will be intermittent.
Show answer & explanationAnswer & explanation
Correct answer: C. The kingpin could separate from the fifth wheel during operation.
If the fifth wheel release arm is not fully seated and locked, it means the fifth wheel jaws are not securely closed around the kingpin. This significantly increases the risk of the kingpin separating from the fifth wheel during turns, bumps, or braking, leading to a catastrophic trailer detachment.
Why the other options are wrong
- A. The fifth wheel release arm's position does not directly affect the air brake system's function.
- B. The landing gear's retraction is a separate mechanical operation, unrelated to the fifth wheel release arm's locked position.
- D. The electrical connection is independent of the fifth wheel's mechanical locking mechanism.
Unsecured Fifth Wheel Release Arm
A condition where the fifth wheel release arm is not fully returned to its locked position after coupling, indicating the kingpin may not be securely held by the jaws.
- High risk of trailer separation.
- Requires immediate correction before driving.
- Often indicates incomplete kingpin engagement.
Memory trick: Lock That Arm, Or Harm Will Come.