CDL Air Brakes TestAir Brake System PartsHard
A driver notices that when they fully depress the brake pedal, the service brakes are slow to respond and feel 'spongy'. However, the air pressure gauges show normal operating pressure. What is the most likely cause?
- AA clogged air dryer.
- BA malfunctioning air compressor governor.
- CA faulty low air pressure warning system.
- DExcessive slack in the automatic slack adjusters.
Show answer & explanationAnswer & explanation
Correct answer: D. Excessive slack in the automatic slack adjusters.
If the air pressure is normal but the brakes feel 'spongy' and slow to respond, it often suggests that the brake components are not being effectively pushed against the drums/rotors. Excessive slack in the automatic slack adjusters means the brake shoes have to travel too far before contacting the drum, leading to delayed and inefficient braking.
Why the other options are wrong
- A. A clogged air dryer primarily affects moisture removal and can lead to air system contamination, not directly a spongy brake feel with normal pressure.
- B. A faulty governor would affect air pressure build-up or regulation, which is stated as normal.
- C. A faulty warning system would not impact the physical braking performance, only the alerts.
Slack Adjusters
Components that adjust the distance between the brake shoes and the brake drum, ensuring proper brake stroke and efficient braking.
- Automatic slack adjusters maintain proper clearance.
- Excessive slack leads to 'spongy' brakes and longer stopping distances.
- Must be checked during pre-trip inspection.
Memory trick: Slack = Slow Stops.