CDL General Knowledge TestCombination Vehicles (if applicable)Hard
A driver is driving a combination vehicle and notices that the trailer wheels are locking up prematurely during moderate braking. Which of the following is the most likely cause?
- AImproperly adjusted trailer brakes.
- BExcessive weight on the tractor's drive axles.
- COverloaded trailer.
- DInsufficient air pressure in the tractor's tanks.
Show answer & explanationAnswer & explanation
Correct answer: A. Improperly adjusted trailer brakes.
Improperly adjusted trailer brakes, especially if they are too tight, can cause the trailer wheels to lock up prematurely before the tractor's brakes have fully engaged or before effective braking occurs.
Why the other options are wrong
- B. Excessive weight on the tractor's drive axles would reduce the likelihood of the tractor's drive wheels locking, but wouldn't directly cause premature trailer wheel lock-up.
- C. An overloaded trailer would typically require more braking force, making it less likely for wheels to lock up prematurely unless the brakes are severely over-adjusted.
- D. Insufficient air pressure would lead to weak braking overall, not premature lock-up of only the trailer wheels.
Trailer Brake Premature Lock-up
When trailer wheels lock before tractor wheels during braking, often due to brake adjustment or loading issues.
- Can lead to trailer jackknife.
- Often caused by improperly adjusted brakes.
- More common with empty or light trailers.
Memory trick: Locking early means adjustment's not pearly.