CDL Air Brakes TestAir Brake System PartsHard
A driver is operating a commercial vehicle and notices that the service brakes feel 'spongy' or require excessive pedal travel to achieve effective braking, even after adjusting the slack adjusters. What is the most likely cause of this symptom?
- AOver-lubricated brake cam shafts.
- BWorn or damaged brake drums/rotors.
- CContaminated brake linings.
- DA faulty air compressor governor.
Show answer & explanationAnswer & explanation
Correct answer: B. Worn or damaged brake drums/rotors.
If the slack adjusters are correctly set, but braking still feels spongy or requires excessive pedal travel, it often points to issues with the foundation brakes themselves, such as worn, cracked, or out-of-round brake drums/rotors. These conditions prevent the brake shoes/pads from making full, consistent contact.
Why the other options are wrong
- A. Over-lubricated cam shafts could cause brakes to stick, but not typically a spongy feel or excessive pedal travel if slack adjusters are correct.
- C. Contaminated brake linings would likely cause reduced braking power and possibly pulling, but 'spongy' feel and excessive travel are more indicative of drum/rotor issues.
- D. A faulty governor would affect air pressure build-up or cut-out, not the feel of the service brakes at adequate pressure.
Foundation Brakes Wear
Degradation or damage to the fundamental components of the braking system (drums, rotors, shoes, pads) that directly produce friction to stop the vehicle.
- Includes brake drums, shoes, linings, cam shafts, return springs.
- Wear affects braking efficiency and can cause various symptoms.
- Requires regular inspection and maintenance.
Memory trick: Healthy foundation, strong stopping sensation!