CDL Combination Vehicles TestCoupling and UncouplingMedium
What is the primary purpose of the 'pull test' performed during the coupling procedure?
- ATo verify that the landing gear is fully retracted.
- BTo ensure the fifth wheel jaws have securely locked onto the kingpin.
- CTo test the functionality of the trailer's lights.
- DTo check the air pressure in the trailer's brake system.
Show answer & explanationAnswer & explanation
Correct answer: B. To ensure the fifth wheel jaws have securely locked onto the kingpin.
The pull test is a critical safety check to confirm that the mechanical connection between the tractor and trailer is secure. By gently tugging the tractor forward against the trailer's set brakes, the driver can verify that the kingpin is firmly locked in the fifth wheel jaws.
Why the other options are wrong
- A. The landing gear is raised after the pull test and air/electrical connections, not verified by the pull test itself.
- C. Light functionality is checked later, after electrical connection and before departure.
- D. Air pressure is checked after connecting the air lines, not during the pull test.
Pull Test
A safety procedure during coupling where the tractor is gently pulled forward against the trailer's set brakes to confirm the kingpin is securely locked in the fifth wheel.
- Confirms mechanical connection.
- Performed after kingpin engagement.
- Crucial safety step.
Memory trick: Pull to prove the lock is true.