ASE A5 Master Cylinder

Question 1

A vehicle's brake pedal slowly sinks toward the floor while steady pressure is held. There are no external leaks and the reservoir level has not dropped. What is the most likely cause?

Accepted Answer

Worn or damaged piston cups inside the master cylinder bore

Answer

A pedal that sinks with no external leak and no fluid loss points to fluid bypassing the master cylinder piston cups internally.

Question 2

During a master cylinder replacement, the pushrod is adjusted too long so that it holds the primary piston forward with the pedal released. Which symptom is most likely?

Accepted Answer

Brakes that drag and overheat because the compensating port stays covered

Answer

A pushrod that is too long keeps the primary cup over the compensating port, so pressure cannot release and the brakes drag.

Question 3

When bench bleeding a master cylinder, why are the bleed tubes or fittings routed back into the reservoir with their ends below the fluid level?

Accepted Answer

To prevent air from being drawn back into the bore on the piston's return stroke

Answer

Keeping the tube ends submerged means that only fluid, not air, is drawn back into the bore when the piston returns.

Question 4

A technician finds brake fluid on the firewall and inside the vacuum booster behind the master cylinder, and the reservoir level keeps falling. What is the most likely cause?

Accepted Answer

A leaking rear (primary piston) seal in the master cylinder

Answer

Fluid at the booster and firewall points to the master cylinder's primary piston rear seal leaking out of the back of the bore.

Question 5

A customer complains that the brake fluid level in the reservoir is slightly lower than at the last service. The vehicle has front disc brakes, and the pads are about half worn. A thorough inspection finds no leaks. What should the technician conclude?

Accepted Answer

The level drop is normal because fluid fills the caliper pistons as the pads wear

Answer

As disc pads wear, the caliper pistons extend farther and take up fluid, so the reservoir level falls gradually.

ASE A5 Practice Test

ASE A5 Practice Test

ASE A5 Master Cylinder