Hairy W Bush

My booster was replaced last year from the previous owner. But I have a very stiff petal with difficult stopping force. I checked the booster and it does not hold any vacuum when i checked it from the valve. The valve itself will hold a vacuum and pressing it against the booster does not make a difference. BUT, when I do the test where you hold down the pedal and start it, it does drop a couple inches.
If it is the booster I think this is what is contributing to my running issues.

Cliff Harris

The diaphragm inside the booster might be leaky but not completely ruptured. The volume inside the booster is pretty large, so it would take quite a while to pump it down with a Mity-Vac or similar tool.

I would try plugging the vacuum line from the plenum and see if the car runs better.

You didn't put in the year, so this might not apply. You might have an ABS issue:

http://forums.corvetteforum.com/1570563275-post316.html

cudamax

Don't get all the things ur complaining about but if a booster goes bad from what I've seen the brake pedal will be rock hard and u will have a hissing noise from the booster thats heard from inside under the dash and when u hit the brake pedal with the engine off and then when u start up, it will not make a difference and the brake pedal does not drop at all So another thing to check for is a frozen caliper piston. Throw it up on jack stands take off all the wheels tighten a few lugs down on each rotors and start pumping on the brakes and make sure each calipers pistons are moving as far as the motor running problem, Dude fix the brakes first then move on. You got to stop before u can go

Hairy W Bush

It's a 95 and I did try those panic stops one day. It might have made a slight difference at the moment, but I am back here with my problem.

no hissing sound and can you elaborate on that test? I don't understand what you're trying to say. there is no pull to the car. my motor running problem is actually a cold stumble for several minutes and a decreased mpg so that's why I thought maybe the booster holding no vacuum would be it.

DanielRicany

Actually, I just had an interesting thing happen to me the other day. This is my first car older than 1999. So I wasn't really sure how the brake pedal felt when this car was made. Cliff Harris posted in another thread to hold the brake pedal and then start the engine, and if it goes down more the booster is working. My pedal was pretty hard and my brakes weren't very good. I did what Cliff said, which worked and then I pumped the pedal and it felt like a modern pedal after that. Which surprised me. Now I'm wondering if something is wrong with mine because maybe over time it will go back to being hard?

cudamax

If when u start it up and the brake pedal goes down. The booster is good and if u pump up the pedal while its running and it gets harder. Air in the system or worn linings/pads or any of the caliper pistons hanging up and not pushing the pads to rest on the rotors

cudamax

Sure if ur pedal is rock hard and does not drop while pushing on it with the engine running. The booster is not holding vacuum and will be leaking somewhere around inside its large drum that usually can be herd while the motors running from the inside of the car somewhere up close by the brake pedal if nothing is herd leaking with a rock hard brake pedal sometime its the little plastic angle connector that the main engine vacuum line connects to that goes into the booster to make it work and or the rubber gorment that that slides into
Also a frozen caliper piston thats not moving or hardly moving with a noticeable pull or not.

Hairy W Bush

I can check to see brake operation then with the car off the ground and turn the wheels and see how they brake I guess. But yes there is a rock hard pedal feel when engine running. The only time it changes is when I do that 'test' I talked about or when I slam on that pedal to stop but the feel does not last long at all. There is also no hissing at all.
I wonder if I can double check the vacuum because Cliff said the diaphragm is huge.

Cliff Harris

I have had a diaphragm rupture and did not hear any hissing. That one happened as I was driving through Santa Barbara on highway 101. I stepped on the brake and it was VERY hard.

The second time was a cracked booster housing, so any hissing was going on in the engine compartment and I did not hear it. That one happened in my garage. I started the engine and as I started to back out I put my foot on the brake pedal and it was VERY hard. I could stop pretty well if I used both feet on the brake pedal.

hooked073

Is the check valve good going to the booster. Something that is offen forgoton

Hairy W Bush

probably my issue then...Is there a way I can be 100% sure before I do this job I'd rather not do? I'm going to check the wheels this weekend but probably wont get to doing it till next weekend.
I believe so. I took it off and itself holds a vacuum. The air also goes out but I cannot blow past it.

Hairy W Bush

Well I checked the booster again tonight. With the hose off it is even harder than I thought a pedal could be. And the idle is actually the same when i plug off the vacuum line and when it's into the booster sooo now I'm thinking it's ok. I kinda figured a vette would have a harder pedal but that doesn't explain my stopping issue. I jacked up the car, spun ALL wheels and they all stopped instantly when the brakes were applied. I'm not sure right now...