Pvette76

The brake booster was disconnected when I bought the car (1976). So I connected it back up and the brakes seem to work fine but I hear a hissing sounds like a vacuum leak. So when I plug up the vacuum hose the noise stops but the car idle does not change. I thought the idle would get worse if it is leaking. So is the hissing sound normal or should I replace the brake booster?

gingerbreadman1977

a hissing sound made from dispelling air is normal when pressing the pedal but if its a continual noise that never stops then you have a bad booster/vacum leak.

Pvette76

I just found the leak. I did replace the master cylinder and it didn't have a gasket. The old one didn't either so I didn't think much of it. But if I put my hand on the bottom I can feel the leak. Some web sites show the gasket and other do not. So I will buy some gasket material or gasket in a tube and see what happens.

Thanks for the help.

anonymizer

I'm going through this right now with my '82. Idle drops with leaky (or bad) PB, but when I open the vac hose (release from PB check valve), idle increases.

'75

The area between the booster and master cylinder needs to breathe. A vacuum leak there indicates the front seal of the booster is leaking. If you seal the two together, you take a chance of sucking brake fluid from the rear of the master into the booster. You either need a new front seal for the booster(which is not readily available) or a new booster.