CDL Air Brakes TestAir Brake System PartsMedium
A driver notices that when they apply the service brakes on a commercial vehicle, the brake pedal feels unusually soft and requires excessive travel before the brakes engage effectively. This issue is most likely related to which of the following?
- AExcessive slack in the foundation brakes' adjustment.
- BA clogged air dryer filter.
- CContaminated air in the storage tanks.
- DA malfunctioning air compressor governor.
Show answer & explanationAnswer & explanation
Correct answer: A. Excessive slack in the foundation brakes' adjustment.
Excessive slack in the foundation brakes (due to improper adjustment of slack adjusters or worn linings) means the brake chambers have to push further before the linings contact the drums/rotors, resulting in a soft pedal with excessive travel.
Why the other options are wrong
- B. A clogged air dryer filter would affect air quality and potentially system performance, but not typically cause a soft brake pedal.
- C. Contaminated air could cause component damage over time but doesn't directly cause a soft pedal with excessive travel.
- D. A malfunctioning governor would affect air pressure build-up or cut-out, not pedal feel directly.
Foundation Brakes (Slack Adjustment)
The mechanical components at each wheel end (e.g., brake shoes/linings, drums, slack adjusters, brake chambers) that physically stop the vehicle. Proper slack adjustment is critical for effective braking.
- Slack adjusters maintain correct clearance between linings and drums.
- Excessive slack leads to long pedal travel and reduced braking force.
- Manual and automatic slack adjusters require proper inspection and maintenance.
Memory trick: Soft Pedal = Slack Problem.