CDL General Knowledge TestAir Brakes (if applicable)Medium
A driver notices that the brake pedal on their air brake equipped vehicle feels 'spongy' or has excessive travel before the brakes engage properly. They also observe inconsistent braking performance. Which of the following is the most probable cause?
- AA seized air compressor.
- BExcessive moisture in the air tanks.
- CA clogged air dryer filter.
- DImproperly adjusted slack adjusters.
Show answer & explanationAnswer & explanation
Correct answer: D. Improperly adjusted slack adjusters.
A 'spongy' pedal with excessive travel and inconsistent braking performance are classic symptoms of improperly adjusted slack adjusters. When slack adjusters are out of adjustment, the pushrod has to travel further than normal before the brake shoes contact the drum, leading to poor braking.
Why the other options are wrong
- A. A seized air compressor would result in a loss of air pressure, not a spongy pedal.
- B. Excessive moisture can cause freezing or corrosion, but a spongy pedal is not its primary symptom.
- C. A clogged air dryer would primarily affect moisture removal, potentially leading to system contamination, but not directly a spongy pedal feel.
Slack Adjuster Maladjustment Symptoms
Improperly adjusted slack adjusters lead to excessive brake pedal travel, a 'spongy' feel, and reduced, inconsistent braking performance.
- Excessive pushrod travel.
- Brakes engage late.
- Reduced braking force.
- Increases risk of brake fade.
Memory trick: Slack too long, the pedal feels wrong.