CDL General Knowledge TestCombination Vehicles (if applicable)Medium
A driver is coupling a tractor to a semi-trailer on a slight incline. After backing under the trailer, what is the most critical step to perform BEFORE raising the landing gear?
- APerform a 'tug test' to ensure the kingpin is locked.
- BApply the trailer parking brakes.
- CConnect the emergency (red) air line to the trailer.
- DConnect the electrical cable to the trailer.
Show answer & explanationAnswer & explanation
Correct answer: A. Perform a 'tug test' to ensure the kingpin is locked.
After backing under, the tug test is essential to confirm the kingpin is securely locked into the fifth wheel. If not locked, raising the landing gear could cause the trailer to fall, especially on an incline.
Why the other options are wrong
- B. The trailer parking brakes should already be applied before backing under, as part of securing the trailer for coupling.
- C. Connecting air lines is crucial, but the mechanical lock must be confirmed before removing the landing gear's support.
- D. Electrical connection is important but secondary to mechanical coupling security.
Coupling Tug Test Importance
The 'tug test' is a vital step after backing under a trailer to physically verify that the fifth wheel locking jaws have securely engaged the kingpin before raising the landing gear.
- Prevents trailer separation.
- Should be done before raising landing gear.
- Especially critical on uneven or sloped ground.
Memory trick: Tug before you lift, or your trailer might drift.