CDL Combination Vehicles TestCoupling and UncouplingEasy
During the coupling process, after backing the tractor under the trailer and connecting the air and electrical lines, a driver performs a 'tug test'. What is the specific purpose of this test?
- ATo check the trailer brake functionality.
- BTo confirm the kingpin is locked into the fifth wheel jaws.
- CTo verify the landing gear is fully retracted.
- DTo ensure the glad hands are securely attached.
Show answer & explanationAnswer & explanation
Correct answer: B. To confirm the kingpin is locked into the fifth wheel jaws.
The 'tug test' or 'pull test' is performed by gently pulling forward against the trailer's set brakes to confirm the kingpin is securely locked in the fifth wheel jaws.
Why the other options are wrong
- A. Trailer brake functionality is checked through separate test procedures.
- C. Landing gear retraction is a visual check done after the tug test.
- D. Glad hand security is visually checked, not primarily by a tug test.
Pull Test (Kingpin Lock)
A test performed during coupling by gently pulling the tractor forward against the trailer's set brakes to ensure the kingpin is securely locked in the fifth wheel jaws.
- Verifies proper kingpin engagement.
- Done after air/electrical connections.
- Prevents trailer separation while driving.
Memory trick: Tug to confirm the connection is snug.