Brakes Brake Booster troubleshooting

[UncleMike]

Pretty sure i have a bad booster, but wanted to run through my troubleshooting to be 100%. Hard pedal, hard to stop. Pedal hard when not running, start up, drops a little and softens a bit. I've smoke tested the vacuum system with line to booster plugged....absolutely no leaks. Check valve works as it should. Removed check valve, smoke tested the booster, and had smoke from rear bellow. Vacuum tested booster....does not hold vacuum.
Brake booster, right? Anything else to check? Only other thing i found was the line to booster (pulling off front vac port of edelbrock avs2) only has about 15" of vacuum at idle...i'm reading at various sites 18" is the minimum....i do have one direct port that is plugged on manifold i could pull from, but don't how that would make that much of a difference.

 

[Patrick]

Did you figure it out…

 

[TSB8C]

Pretty sure i have a bad booster, but wanted to run through my troubleshooting to be 100%. Hard pedal, hard to stop. Pedal hard when not running, start up, drops a little and softens a bit. I've smoke tested the vacuum system with line to booster plugged....absolutely no leaks. Check valve works as it should. Removed check valve, smoke tested the booster, and had smoke from rear bellow. Vacuum tested booster....does not hold vacuum.
Brake booster, right? Anything else to check? Only other thing i found was the line to booster (pulling off front vac port of edelbrock avs2) only has about 15" of vacuum at idle...i'm reading at various sites 18" is the minimum....i do have one direct port that is plugged on manifold i could pull from, but don't how that would make that much of a difference.

I believe you found the issue. Those things don't go bad too often, but they do. When I converted to power brakes, the new booster was bad out of the box. Didn't want to believe it and kept looking for something else, since I had installed a new prop valve, master cylinder, and such for the conversion. But it was the booster when I tested and it didn't hold vacuum.

 

[gert]

15 inches of vacuum should be enough, it might not give maximum effort from the booster but if it wont hold vacuum its toast