Brake Booster Not Working?

[Toner]

Any help Guys...
I don't think my brake booster is working as the pedal does not move when starting the GT. Prior to installing the MC I started the engine for testing, it ran real rough but only to find out air was sucking into the booster where the MC mounts, is this normal? I plugged the hole with piece of cardboard and the engine ran fine(no vac. leak). After installing the MC the car is real hard to stop. What was done: rebuilt MC, new rotors;/disc pads and new front hoses, new rear brake shoes, turned drums, new wheel cylinders, new hose and bleed till no more bubbles. All clean fluid in and clean coming out. Forgot to say I also adjusted the rear pads and e-brake to five clicks.
Any ideas?

[newman27]

I'm no expert (in fact I rarely comment on things like this because others on here know 10,000X what I do) but those symptoms do sound similar to the time I had a brake booster issue. Does the engine rev when you apply the brake pedal? If so, you may have a problem with the booster leaking. Do you have the check valve in-line with the vacuum hose that runs from the booster to the engine? Just a couple simple things to check...

Matt

[David McCollam]

By meaning "car is hard to stop", do you mean the brake pedal requires a great deal of effort? If so, inspect the in-line check valve. If the check valve is reversed you will not get any assist from the manifold vacuum source and it will require additional effort to depress the pedal. Just turn the check valve and hose around from the current installation. If it decreases pedal effort, that was your problem.

[Toner]

Vac. hose installed the way it came out, I get good suction when I pull the hose off the booster. I can pump the pedal and the engine does not change RPM. And yes it requires a great deal of effort to stop the car, worked fine 23 years ago .

[Toner]

Thanks, I will reverse the hose tonight after work and see if it fixes it.
Scott

[BDD]

A failing brake booster will result in a very stiff brake pedal because it's not assisting you in activating the master cylinder. The stock booster probably doubles the force you put into the pedal. This is what my car was like and apparently the booster was not working. The master cylinder was also leaking into the brake booster. This would have caused the booster to fail.

There are some informative posts on how to check the booster to see if it's working, may have brake fluid leaking into it, etc.

With my car, even though the above things were true (per the mechanic who worked on it) pressing the brake pedal did not cause a change in rpm. There was also no white smoke in the exhaust and I saw no brake fluid in the vacuum line. I never got to do the test doing a hard left turn or u-turn to see if a cloud of white smoke resulted.

The big symptom for me was that you really had to apply a lot of force to get the brakes to work.

When my booster was replaced with a new one apparently the last vacuum leak that I was tracking down was fixed. I'll have to drive it more to be sure but when I drove the car home there was no tendency to backfire and I noticed no hesitation on pressing the accelerator pedal. Backfiring is a common symptom of vacuum leaks.