Preventing Master Cylinder Damage During Service

Problem: "No pedal" condition after brake pad replacement or foot bleeding a vehicle



Cause: The primary cup seals operate in a small area in the master cylinder bore. The area where normal piston travel occurs is cleaned with every brake apply.



The unused area of the master cylinder bore accumulates with sludge and corrosion over time. (See Figure 71.1) This buildup is accelerated by a lack of periodic brake fluid flushing. If the brake pedal travel is great enough to push the primary cup seals into the unused area of the bore cup seal damage could occur.



 Figure 71.1



Solution: Excessive brake pedal travel can take place when pumping the caliper pistons out after a simple friction reline or during foot bleeding. A generally accepted rule of thumb is to NEVER exceed 3/4 pedal travel when applying the brake pedal.



TIP: Some shops require the technicians to place a 2x4 under the brake pedal to make sure the brake pedal travel doesn't exceed 3/4.