CDL Combination Vehicles TestDriving Combination Vehicles SafelyHard
A commercial driver operating a combination vehicle notices that the trailer brakes are locking up frequently during light braking, while the tractor brakes are functioning normally. What is the most likely cause of this issue?
- AThe service brake pedal is being applied too aggressively for the conditions.
- BThe tractor's air compressor is failing, leading to uneven air pressure.
- CThe trailer is empty or very lightly loaded, causing the brakes to be overly sensitive.
- DThe glad hand connections between the tractor and trailer are loose.
Show answer & explanationAnswer & explanation
Correct answer: C. The trailer is empty or very lightly loaded, causing the brakes to be overly sensitive.
When a trailer is empty or very lightly loaded, its brakes can be overly sensitive compared to the tractor's brakes. With less weight pushing down on the wheels, even light braking can cause the tires to lose traction and lock up, especially if the brake adjustment is not optimal for an empty load.
Why the other options are wrong
- A. While aggressive braking can cause lock-ups, the question specifies 'light braking' and indicates the tractor brakes are fine, pointing to an issue specific to the trailer's load condition rather than driver input.
- B. A failing air compressor would likely affect both tractor and trailer braking, or show up as low air pressure warnings, not just trailer lock-up.
- D. Loose glad hand connections would more likely lead to air leaks, which would reduce overall braking effectiveness or cause constant cycling of the compressor, not necessarily frequent trailer lock-ups during light braking.
Trailer Brake Lock-up (Lightly Loaded)
Lightly loaded or empty trailers are prone to brake lock-up during light braking due to insufficient weight for traction.
- Less weight = less traction.
- Trailer brakes become overly sensitive.
- Requires careful brake application and potentially adjustment.
Memory trick: Light Load, Locking Wheels, Lose Control.