Rock hard break pedal

[blackazz]

I have vac breaks. pedal is great but the min I get under the boost an try to stop the pedal is hard as a rock. an I can't stop only acts like that under boost.I do have vac port. did my booster just cap out on me? Thanks for any help

 

[Phoneguy]

That is exactly why they didnt come factory with vacuum brakes.....there is no vacuum under boost. I would test the check valve at the booster though to see if it is sticking. Once you are out of boost the brakes should return to normal.

Bryan

 

[chopped39]

Check valve has to be bad. Is this a new install?

 

[blackazz]

I'd say about 4yrs new. Just started the other day.I'll look into the check valve.

 

[chopped39]

I'd say about 4yrs new. Just started the other day.I'll look into the check valve.

Start the car and let run for a minute and shut off car. after shutting off wait a minute and pull valve from booster.You should hear vacuum sound if not replace valve. Do you hear any noise in the car when applying brakes?

 

[Buick Mark]

That is exactly why they didnt come factory with vacuum brakes.....there is no vacuum under boost. I would test the check valve at the booster though to see if it is sticking. Once you are out of boost the brakes should return to normal.

Bryan

Yep! But back to your issue, its either the booster itself or the check valve as others have said.

 

[blackazz]

Well I'm not hearing nothing as to air noise inside.going to start her up an see if I can charge the system an see where it goes from there.gabbing a check valve to. I'll report back my findings.

 

[Nick Micale]

That is exactly why they didnt come factory with vacuum brakes.....there is no vacuum under boost........................Bryan

You have stated another "internet myth" Bryan, if that was the case GM would not have used vacuum brakes on the turbo Trans Am, or on the many other models with turbos?

Chrysler built millions of turbo cars with vac brakes as well?

As soon as the throttle is closed there is vacuum, and besides the booster will hold enough vac for more than one stop is it is working properly.

There are a few possible reasons for his issue, if it is a dual diaphragm booster, one or both diaphragms may have a small leak, or the vac plumbing/hoses could be bad, the vac reservoir may not be hooked up, and if the wrong type hose from the vac source is used to supply the booster it could be collapsed on the inside and restricted the vac source.

Having done over 100 of these conversions, the vac system has always outperformed the PM when done properly.

When I was dealing with the GM engineers at the Proving Ground in the '80's, according to them it was NOT the turbo that dictated the PM, as it was also used on the mid-80's Regal station wagons, and their objective was field testing of the forth coming ABS systems which used a very similar system, look at a 1989 Cadillac PM brake booster with ABS sometime!

 

[Phoneguy]

Nick ,
The truth of the matter is that most people do not install a reservoir for vacuum. ..so they don't have a reserve and a faulty valve can be disastrous.
Done properly is a different story

Bryan

Posted from the TurboBuick.Com mobile app

 

[Nick Micale]

Bryan, the factory installed vacuum reservoir is under the core support at the front of the driver fender.

After many years and mods, these canisters are often removed or disabled.

 

[Phoneguy]

Correct. ..
Bryan

Posted from the TurboBuick.Com mobile app

 

[John Larkin]

The easiest way I have found to check the system is start the car, let it idle for a few minutes. Then pull the line out of the brake booster and see if it creates a whoosh of vacuum. If no, then the booster is probably toast. I pulled one from a junkyard and the darn thing still had vacuum in it after sitting for years. Kind of like Nick said, there should be more than enough vacuum in one to stop the car easily even if the engine stops.

 

[blackazz]

The easiest way I have found to check the system is start the car, let it idle for a few minutes. Then pull the line out of the brake booster and see if it creates a whoosh of vacuum. If no, then the booster is probably toast. I pulled one from a junkyard and the darn thing still had vacuum in it after sitting for years. Kind of like Nick said, there should be more than enough vacuum in one to stop the car easily even if the engine stops.

Bingo your the winner.I have no vac built up, its the same running or not.Thanks