CDL General Knowledge TestDriving SafelyMedium
You are driving a commercial vehicle equipped with hydraulic brakes and notice the brake pedal feels 'spongy' or goes to the floor. What is the most likely cause of this issue?
- AWorn brake linings.
- BAir in the hydraulic lines.
- CLow air pressure in the brake system.
- DOver-adjusted brakes.
Show answer & explanationAnswer & explanation
Correct answer: B. Air in the hydraulic lines.
A spongy brake pedal in a hydraulic system is typically caused by air trapped in the hydraulic lines. Air compresses, unlike brake fluid, leading to a soft or unresponsive pedal.
Why the other options are wrong
- A. Worn brake linings would cause the pedal to travel further, but might not feel 'spongy' unless accompanied by other issues.
- C. Low air pressure affects air brake systems, not hydraulic systems.
- D. Over-adjusted brakes would likely cause the pedal to be high and hard, not spongy.
Spongy Hydraulic Brakes
A brake pedal that feels soft, spongy, or goes to the floor, most often caused by air in the hydraulic lines.
- Air in the system compresses, fluid does not.
- Reduces braking effectiveness.
- Requires bleeding the brake system to resolve.
Memory trick: Spongy pedal? Air in the Fluid, not good!