CDL Combination Vehicles TestCoupling and UncouplingEasy
During the coupling procedure, after backing the tractor until the fifth wheel is under the trailer and the kingpin is locked, what is the next safety check a driver should perform before raising the landing gear?
- AVisually confirm that there is no gap between the fifth wheel and the trailer apron.
- BAdjust the fifth wheel height to ensure proper weight distribution.
- CConnect the glad hands to the dummy couplers on the tractor.
- DRelease the trailer parking brakes and check for air leaks.
Show answer & explanationAnswer & explanation
Correct answer: A. Visually confirm that there is no gap between the fifth wheel and the trailer apron.
After the kingpin is locked into the fifth wheel jaws, it is crucial to visually inspect that the fifth wheel plate is fully against the trailer apron. This confirms a secure connection and prevents 'high coupling', which can be very dangerous.
Why the other options are wrong
- B. Fifth wheel height is adjusted before backing under the trailer; proper weight distribution is a result of correct coupling, not an immediate next step after kingpin lock.
- C. Connecting glad hands to dummy couplers is done when uncoupling or parking, not during coupling.
- D. Releasing trailer brakes and checking for air leaks occurs after connecting air lines and performing a pull test, not immediately after kingpin lock.
Fifth Wheel to Apron Contact
Ensuring the fifth wheel plate is fully in contact with the trailer's apron after the kingpin is locked, indicating a secure and safe coupling.
- Prevents high coupling.
- Confirms kingpin is seated correctly.
- Essential safety check before moving.
Memory trick: Always Double Check Connections Before You Roll.