CDL General Knowledge TestAir Brakes (if applicable)Medium
A technician is troubleshooting an air brake system. They find that the brake pedal feels spongy and requires significantly more travel than usual before the brakes engage. What is the most probable cause?
- AA properly functioning air dryer.
- BThe air compressor cut-in pressure is too high.
- CExcessive slack in the brake adjusters.
- DA faulty low air pressure warning alarm.
Show answer & explanationAnswer & explanation
Correct answer: C. Excessive slack in the brake adjusters.
Excessive slack in the brake adjusters means the pushrod has to travel further to move the brake shoes into contact with the drum, resulting in a spongy pedal feel and delayed brake engagement. This also reduces braking effectiveness.
Why the other options are wrong
- A. A properly functioning air dryer removes moisture and would not cause a spongy pedal or excessive travel.
- B. High cut-in pressure would affect when the compressor starts, not the pedal feel or travel once air is available.
- D. A faulty warning alarm affects notification, not the physical feel or function of the brake pedal itself.
Slack Adjuster Maladjustment
When the automatic or manual slack adjusters are not correctly set, leading to too much clearance between the brake shoes and drum.
- Causes excessive brake pedal travel.
- Reduces braking effectiveness.
- Can lead to brake fade.
Memory trick: Slack is too much, brakes don't touch.