CDL Combination Vehicles TestCoupling and UncouplingMedium
Before backing the tractor under a trailer for coupling, a driver should ensure the trailer's landing gear is fully extended and supporting the trailer. Why is it important for the landing gear to be fully down and stable, even if the trailer's nose height is already correct?
- ATo prevent brake lock-up during coupling.
- BTo provide a stable platform in case the kingpin or fifth wheel fails during coupling.
- CTo ensure the trailer's weight is not solely on the fifth wheel during the initial connection.
- DTo allow for easier connection of air and electrical lines.
Show answer & explanationAnswer & explanation
Correct answer: B. To provide a stable platform in case the kingpin or fifth wheel fails during coupling.
Even if the trailer's nose height is correct, the landing gear must be fully down and stable. This provides crucial support and prevents the trailer from tipping or falling if there's an issue with the kingpin engaging the fifth wheel, or if the fifth wheel itself fails during the coupling process. It's a critical safety measure.
Why the other options are wrong
- A. Landing gear position does not directly affect brake lock-up during coupling.
- C. The trailer's weight is not on the fifth wheel until coupling is complete. The landing gear supports it beforehand.
- D. While stability helps, the primary reason is safety against trailer collapse, not ease of connection.
Landing Gear Stability for Coupling
Before coupling, the trailer's landing gear must be fully extended and stable to prevent the trailer from tipping or collapsing in case of a kingpin or fifth wheel coupling failure.
- Provides structural support for the trailer.
- Prevents trailer from falling if coupling fails.
- Ensures stability during the coupling sequence.
Memory trick: Gear Down, Ground Firm, Safety's Confirmed.