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Old 06-21-2010, 10:27 PM   #1 (permalink)
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Default Brakes don't release pressure, help

Saturday I was driving and I eventually got the feeling something was holding back my car. Thinking it was a really low, or flat tire I pulled over at a gas station to get air... the tires are fine. So I get in the car and start driving again, and it gets to the point that I was in boost just to keep cruising. I pulled over and found out that all four rotors and/or pads were smoking a little bit. Also the brake pedal was rock hard.

I let the car sit for about 15 minutes, got in the car, started it and it was back to normal. I drove the car home.

It felt/seemed as if while I let the car sit something having to do with the brakes released/adjusted vacuum or pressure levels.

Do these cars have any one way valves or anything that could be failing? What exactly makes the pressure release from the brakes on these cars?

Thanks, -Evan
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Old 06-21-2010, 10:30 PM   #2 (permalink)
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Default Re: Brakes don't release pressure, help

Also, I've had my clutch booster removed for over a year, maybe two at this point. IIRC there is a check valve in the line NEAR the brake booster, but I'm not sure if it has to do with it.
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Old 06-21-2010, 11:43 PM   #3 (permalink)
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Default Re: Brakes don't release pressure, help

I'd start with changing the brake fluid. Flush all the old out with new.

The brake booster check valve is in the hose off the back of the intake manifold to the booster.

If you said one brake rotor was getting hot I would say a collapsed line, but all four, I suspect contaminated fluid boiling causing the brakes to self apply. The 15 minute break gave the fluid time to cool down and contract releasing the brakes.

Jeff
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Old 06-22-2010, 06:31 PM   #4 (permalink)
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Default Re: Brakes don't release pressure, help

Thanks for the reply, and your probably right.

As stupid as this is, a few months ago I added what I thought was brake fluid to the reservoir. It wasn't... it was power steering fluid. I figured since it was a tiny tiny amount I'd be fine. Well, apparently not. Again, stupid stupid stupid.

And you know it took balls to admit that one, but as long as it helps figure out the problem .

-Evan
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Old 06-22-2010, 06:33 PM   #5 (permalink)
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Default Re: Brakes don't release pressure, help

This has been posted about before. Its not boiling fluid. Its either a vacuum issue at the booster, or the master cylinder is causing issues.
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Old 06-22-2010, 07:09 PM   #6 (permalink)
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Default Re: Brakes don't release pressure, help

Looks like I have some searching to do. I hope its not the master cylinder.
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Old 06-23-2010, 04:42 AM   #7 (permalink)
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Default Re: Brakes don't release pressure, help

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Originally Posted by Stealthee View Post
This has been posted about before. Its not boiling fluid. Its either a vacuum issue at the booster, or the master cylinder is causing issues.
How does vacuum at the booster self apply the brakes, and even then only when hot? The worst case scenario I see with the booster is the pedal being firm from a busted diaphram and no vacuum assist, not self applying.

The master cylinder, I could see now that OP has stated he used PS fluid in the brake system, but it doesn't explain why they released when they cooled. A misadjusted pedal maybe but I'm assuming OP didn't have this issue before he added fluid to the system.

An overfilled system WILL do this once the fluid gets hot and expands.

PS fluid in the brake system will swell the seals in the brake system. Flush the system with clean brake fluid.

Jeff
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Old 06-23-2010, 07:38 AM   #8 (permalink)
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Default Re: Brakes don't release pressure, help

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Originally Posted by kywhitelightning View Post
How does vacuum at the booster self apply the brakes, and even then only when hot?
It doesnt and cant.

The clue to the real problem is that the lockup happens when hot.

The reason is that the compensation port is not open when there is no pressure on the pedal. This can be from pedal problems or the pushrod in the booster not being adjusted properly.

-SP
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