Hissing from “Rebuilt” brake booster

[1KoolBee]

So I recently replaced the power brake booster in my 66 Satellite with a “ rebuilt” one. It works fine but it makes a hissing noise when the pedal is not pushed in. The motor is not happy about the vacuum leak. I’ve found if I push the pedal in about 1/8”, the hissing goes away, and the motor is happy. Is there an adjustment that can be made to the master cylinder rod or the pedal linkage to solve this problem? Or is booster hosed?

 

[Dave6T4]

Take it back. Something wrong there.

 

[1KoolBee]

Seems like it would be way easier if there was a simple adjustment.

 

[steve340]

The post #2 is right the booster probably has a fault. Is the pedal pushrod adjustable?
Some can be adjusted but it may be waste of time.
There is an air valve at the back of the booster were the pushrod goes in that is leaking.
It might settle down after a few applications but failing that you would need to take the booster back out.

 

[Ron H]

Kind of odd as in my experiences there’s been issues with a pre-load, can be caused by the pedal ‘home’ position binding against the brake-light switch. These hassles were the reverse of what you mention. I’d check to make sure there is some free play in the home position. Yeah, other check could be the booster to MC gap, this usually calls for around a 10-thou ‘gap’ btw the MC piston and booster rod tip. Suppose booster rod might be – being forced back too far if no gap? Just a quick thought. Had a problem with one booster and everything ‘checked’ good; but damn, it wasn’t, getting another one…problem solved.