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View Full Version : Might have a failing brake booster



quick35th
09-01-2007, 11:49 PM
Guys my brake booster on my race car might be leaking vaccum. I bled the crap outta the brakes today and all I got was a somewhat decent peddal but after the engine ran for a little bit the peddal went completely soft again.

What I'd like to know is if there is a way to test if I actually do have a failing brake booster. Its important to note that I am not running the Teves master cylinder but I am using the conventional setup that people run.

If I find that the booster is good could it be that the engine is not putting out enough vaccum to power the brakes? I only have a TFS stage one cam so I can see that being the issue. Would the tune of the carb make it produce less vaccum?

I am just trying to think of all the possibilities so I can run down the list tomorrow.

Shane

blown94cougar
09-01-2007, 11:59 PM
Get a vacuum hand pump type tester pump it up let it set for 10 minutes hook the tester pump to the big vaccum line ....if the press bleeds off its a bad booster if it does not its something else ...that cam isnt enough to lower vaccuum to where the booster dont work check for a vaccum leak at the vacuum "tree" driver side under the firewall if the booster was bad you'd get a hard pedal anyway not a soft one

blown94cougar
09-02-2007, 12:01 AM
I'd look for leaks in the brake lines...did you make the lines yourself? if so did you double flare them? could be a bad master cylinder did it set long without lines? could be water moisture in them

racecougar
09-02-2007, 01:09 AM
Would the tune of the carb make it produce less vaccum?

Absolutely...that's how you tune a carb (with a vacuum gauge).

-Rod

quick35th
09-02-2007, 09:05 AM
blown94cougar,

I dont have a vacuum tree, the big vacuum line from the booster goes straight to the back of the intake manifold. I bet autozone has one of those hand pumps so I'm going to have to stop by there today.

Yes it did sit for a while (over six months) without lines connected to the master since last time it was used. I know Sean pushed on the pedal a few weeks ago before I had any lines connected to it and obviously no brake fluid in it. Ever since then its made a funny noise.

Shane

ps, On the rear caipers is the bleeder value above or below the brake line?

CMac89
09-02-2007, 09:36 AM
If you push on the pedal without any fluid in the reservoir then the master cylinder draws air. This is part of the reason why you need to bleed the master cylinder, anyways. Been through this many times and that may be your problem. Does the pedal start out soft, but gets firm the more you push it?

Bleeding the master cylinder is a little different then bleeding brakes.

birds4us
09-02-2007, 09:48 AM
Sounds to me like you have air in the system. Sometimes it can be a pain in the you know what.

quick35th
09-02-2007, 10:20 AM
Well after looking at Sean's cougar I've realized that Lawrence put the rear caipers on oposite sides :rolleyes: So I am going to fix that really fast and see if it clears up my issue.

Shane

deepbluesc
09-02-2007, 10:26 AM
to put both calipers on the same side?:eek: LOL.

Anyway, I would suggest your problem has more to do with the hydraulics and little to do with the booster.

You can bleed the master on the car a couple of different ways. Ask if your not sure.

quick35th
09-02-2007, 01:15 PM
to put both calipers on the same side?:eek: LOL.

Anyway, I would suggest your problem has more to do with the hydraulics and little to do with the booster.

You can bleed the master on the car a couple of different ways. Ask if your not sure.

No actually the brakes are working now. The calipers being on the wrong sides made it so that air was getting trapped inbetween the brake line and the bleeder. The bleeder needs to be above the line to get all the air out of the lines. So after swapping the calipers and rebleeding the brakes they work now.

Thanks guys for the help.

Shane