CDL General Knowledge TestCombination Vehicles (if applicable)Hard
A driver notices that during a full brake application, the trailer brakes lock up before the tractor brakes. What is the MOST likely cause of this issue?
- AThe trailer's service brake chambers are too small.
- BThe trailer is empty or very lightly loaded.
- CThe glad hand seals are worn out.
- DThe tractor's air pressure is too high.
Show answer & explanationAnswer & explanation
Correct answer: B. The trailer is empty or very lightly loaded.
Trailer brakes locking up prematurely is a common issue when the trailer is empty or lightly loaded. The braking system, designed for a full load, applies too much force for the reduced weight, causing the wheels to skid.
Why the other options are wrong
- A. Small brake chambers would result in *less* braking force, making lock-up less likely, not more likely.
- C. Worn glad hand seals would cause air leaks, leading to *reduced* trailer braking or no braking at all, not premature lock-up.
- D. Tractor air pressure being too high would affect both tractor and trailer brakes, not specifically cause trailer lock-up first.
Trailer Brake Lock-up (Light Load)
When the trailer's wheels skid during braking due to excessive braking force for its actual weight, often occurring when the trailer is empty or lightly loaded.
- Common with empty or light trailers.
- Can lead to jackknifing.
- Requires careful brake application and adjustment.
Memory trick: Weight matters, too little makes the trailer slide.