pg
Posts: 1066
Joined: 8/7/2006
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Why is the pedal harder to push when there is no vacuum?
The booster has 2 chambers seperated by a diaphragm. When the motor is running both chambers get vacuum. When you step on the brake pedal you allow atmospheric air pressure to enter the rear chamber, the vacuum is greater than the AAP and pulls the mechanical parts foward and the car slows and stops.
What if the motor stalls?
The check valve will hold some vacuum. Each time you pump the brakes you use up some of the reserve vacuum. Once all the vacuum is gone you can still stop the car with the mechanical parts in the booster. There are springs in the booster that must be compressed by extra pressure on the brake pedal, and thats why the pedal seems harder when there is no vacuum.
An easy test to see if a power booster is working:
With the motor off pump the brake pedal 5 or 6 times to bleed off all vacuum. Release the brake pedal than apply light pressure. Than hold that light pressure and start the motor, if the booster is working the pedal will go down a little. PG.
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my Vettes birthday, May 1, 1974
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RE: Brake Issues - 
