Condition

Weak or no power assist.

Cause

Insufficient vacuum volume to operate booster at maximum efficiency.

Repair Procedure

Check vacuum draw available with a gauge connected between engine and booster. At idle, healthy engines draw somewhere between 17 and 22 inHg.

Check vacuum by depressing brake pedal firmly until it stops. The gauge should read a drop to approximately 10 inHg and then quickly recover to a normal reading. If vacuum takes too long to recover, there is a restriction in the volume (i.e., fitting clogged or vacuum hose collapsed). Repair as necessary.

While a defective booster will cause a hard pedal, a spongy or low pedal requires a hydraulic system check.

Courtesy of CARDONE ProTech