vacuum booster Archives - Brake & Front End
Failed Brake Booster Seal Causes Master Cylinder Leak

Chronic master cylinder failure due to fluid leaking past secondary seal in the master cylinder bore. A defective master cylinder pushrod seal in the power brake booster allows vacuum to draw fluid past secondary seal of the master cylinder.

Vacuum Power Assist Service

Most late-model vehicles use a vacuum booster to help apply the brakes. The booster is usually located behind the master cylinder on the firewall. A leak in the vent valve can cause a reduction in the performance of the booster and increase pedal travel. A manifold vacuum of 20 inHg or greater can be achieved during deceleration. The booster chambers can be evacuated and retained at this pressure by a properly operating check valve.