Power Brake Issue

Is any member a brake expert? I have power brakes and have a hard pedal. The power booster does not seem to be working. It is getting vacuum. When I pump the brake several times and then start the car, the pedal does not move so it indicates there is a problem within the booster (Kelsey Hayes unit). I disconnected the booster from the pedal and there is no difference in the pedal hardness, which tells me the booster is defective in some way. When I put a vacuum pump on the unit, the vacuum pressure holds, so it doesn't appear there are any leaks. What parts inside the bellows could fail that would cause the unit not to work properly? Would a failed vacuum valve, a failed air valve or a failed vacuum balancing diaphragm cause the unit to malfunction? Has anyone rebuilt a Kelsey Hayes unit? Any help is greatly appreciated.

I am not an expert. I don't know if this will help or not, but I saved this info (probably got if from this forum at one time) just in case I ever needed it. It may have the info you're looking for.

https://ranchwagon.wordpress.com/tag...brake-booster/

Thanks. That information will be helpful.