CDL Combination Vehicles TestCoupling and UncouplingMedium
When coupling a tractor to a trailer, after backing the tractor until the fifth wheel is under the trailer and the kingpin is locked into the fifth wheel jaws, what is the next step to ensure a secure connection?
- ALower the fifth wheel to its lowest position.
- BPerform a 'pull test' by gently tugging against the trailer brakes.
- CRaise the landing gear completely.
- DConnect the air lines and electrical cable.
Show answer & explanationAnswer & explanation
Correct answer: B. Perform a 'pull test' by gently tugging against the trailer brakes.
After the kingpin is believed to be locked, a 'pull test' is crucial to verify the secure connection before proceeding with further steps like connecting air lines or raising landing gear.
Why the other options are wrong
- A. The fifth wheel height is adjusted during coupling, not typically lowered after the kingpin is locked.
- C. Raising the landing gear completely is done after the pull test and connecting all lines.
- D. Connecting air lines and electrical cable comes after verifying the mechanical lock.
Pull Test (Coupling)
A pull test is a critical safety check during coupling, where the driver gently pulls the tractor forward against the trailer's set brakes to confirm the kingpin is securely locked in the fifth wheel jaws.
- Verifies mechanical lock.
- Performed before connecting air/electrical.
- Prevents trailer separation during driving.
Memory trick: Lock it, Tug it, Check it.