how to tell if a booster is bad

[bean]

my 72 sat in a field for some 7+ years. the master cylinder is completely rusted out was going to replace it but what about the booster? how do you tell if it is bad? thanks

[71GMCinTN]

Others can give you a better answer, but one sure sign is an air sound, when you push on the brake pedal. (and a vacuum leak at the same time)

[Fitz]

Originally Posted by 71GMCinTN

Others can give you a better answer, but one sure sign is an air sound, when you push on the brake pedal. (and a vacuum leak at the same time)

Another way to test it is start the motor with the manifold vacuum line attached to the booster. Turn the key off and wait 1/2 hour. Pull the vacuum check valve out of the booster. If you hear a sucking sound the booster is good. If not, either the one way check valve needs to be replaced or the diaphragm in the booster leaks. You can test the check valve bu sucking on the inlet...if it passes air, blow into it...it should close preventing any air passing through it. If it works correctly, you have a bad booster.