My brakes lock up after accelerating... - Subaru WRX Forum
 
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post #1 of 6 Old 07-02-2010, 11:52 PM Thread Starter
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My brakes lock up after accelerating...

After I put my foot into it and build full boost in any gear, then try to hammer the brake pedal, it's totally locked. It takes a full second to two for it to release so my foot depresses it and then I have control. Only after acceleration, it's a little softer if I don't build full boost, but basically any accelerating. Also, when I shut the car off the pedal gets stiff and pushes back into it's regular position immediately.

The only other changes are I did the pads right before this happened, and opened the bleeder valves to push the pistons out a bit for space, then closed the valves. I didn't think they got air, and so didn't bleed them. And they don't seem to be spongy...
I changed some vacuum lines to pretty up the engine bay, vac leak?
The only other thing is about when this started the airbag light came on.


I was going to bleed them before posting, but that hardly seems likely to cause this...

*be out of town for the weekend, get back to you guys after, thanks in advance for the help*

355 awhp fp green six speed wagon in Corvette Atomic Orange
-Brandon

Last edited by Chase; 07-03-2010 at 02:22 AM.
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post #2 of 6 Old 07-03-2010, 12:01 PM
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well your brake booster/assist works off engine vacuum to allow easier braking. Sounds to me like you either have a problem with your booster or there may be a check valve that you removed from the system. The booster is designed to hold a reserve of engine vacuum to allow one maybe two assisted brakings after the engine has been shut off or when under boost, no eng. vacuum(not sure why you would be braking under boost anyhow). This is either achieved by an internal check valve on the booster itself of one on the vacuum supply line to the booster. I'd check your vacuum line delete that you mentioned first. If you had a leak, you'd have other issues as well, car would not run well.
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post #3 of 6 Old 07-05-2010, 02:18 PM
 
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If you removed the booster hose, then yeah, you're missing the check valve. It's in the line, and is directional. If you put the hose in backwards it will make for an extremely firm pedal (barely drivable). I learned that the hard way on a basket case impreza I rebuilt. It took me a while to figure that one out, and why the hose was backwards, I'll never know....
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post #4 of 6 Old 07-05-2010, 09:39 PM Thread Starter
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Hey thanks guys, I got to thinking about it camping this weekend, and ya, I think I put that valve in backward. Just a little plastic double nipple, one end more restrictive right?

And yes, it's running crappy. I had 2 people ask me if I did my cams because the idle sounds so lobey, lol.

355 awhp fp green six speed wagon in Corvette Atomic Orange
-Brandon
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post #5 of 6 Old 07-06-2010, 10:20 AM
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Quote:
Originally Posted by Chase View Post
Just a little plastic double nipple, one end more restrictive right?
A check valve allows flow in one direction but not the other, 100% restrictive in one direction 0% restrictive in the other (it's actually a little more than 0 since it has to have enough force to overcome the mechanism that closes the line).

Ryan
2009 STi - Cobb Stage 2
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post #6 of 6 Old 07-06-2010, 12:42 PM Thread Starter
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Got ya, I think I know which line had it. I'm going to put it back in today, I'll let you know if that cures it.

355 awhp fp green six speed wagon in Corvette Atomic Orange
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