Automobile & Light Truck Certification Test A5 BrakesHydraulic System Diagnosis and RepairMedium
A technician is inspecting a vehicle with a complaint of a squealing noise during braking. They find that the front brake pads are severely worn, and the brake fluid reservoir is noticeably low. What is the most appropriate immediate action regarding the brake fluid?
- AAdd fluid only after replacing the worn brake pads.
- BFill the reservoir to the MAX line with new fluid.
- CDo not add fluid, as the level will rise when new pads are installed.
- DAdd fluid until the warning light turns off.
Show answer & explanationAnswer & explanation
Correct answer: A. Add fluid only after replacing the worn brake pads.
When brake pads wear, the caliper pistons extend, drawing fluid from the reservoir and causing the level to drop. Adding fluid before replacing the pads would result in an overfilled reservoir once the new, thicker pads are installed and the pistons retract.
Why the other options are wrong
- B. Filling the reservoir now would likely cause an overflow once new pads are installed and pistons are retracted.
- C. While the level will rise, it's possible it won't be sufficient after pad replacement. The best practice is to add fluid *after* pad replacement to the correct level.
- D. Adding fluid until the warning light turns off without addressing the pad wear is a temporary fix and will lead to overfilling later.
Brake Fluid Level and Pad Wear
The brake fluid level in the reservoir naturally drops as brake pads wear because the caliper pistons extend, drawing fluid into the calipers. Adding fluid before replacing pads can lead to overfilling.
- Low fluid due to pad wear is normal
- Add fluid AFTER pad replacement
- Overfilling can cause overflow or issues
Memory trick: Pads wear down, fluid goes low, replace the pads, then let the fluid flow!