9 bolt Brakes do not seem to hold
 

This is on an 89 rear with PBR's. New pads and Rotors. Brakes have been bleed several times. When car is in gear and rear end is up tires keep turning even if I put the brakes on. I cant get plates for my car cause they wont test it. Any ideas?

Could well be your proportional valve. Did you change the axle recently? Is a new one? If so and you upgraded from drum then that could be the problem...

If not then it could be a slave cylinder?

Stock rearend. Had it removed 2 years ago to paint it but that was all. What I'm thinking is that in gear , (900 rpm) due to the new motor configiration, the backs are having a hard time holding that but when the old motor was in there at a 550 RPM the brakes held. what ya think/>

This is a common complaint. In fact, I'm dealing with the same issue. I'm installing a new combo valve and master cylinder as part of my 1LE front brake upgrade; it will be interesting to see what kind of improvement I get in the rear brake bias. If I don't see improvement I'm installing a Wilwood adjustable prop valve.

I installed the Baer sport kit in front without changing anything else last year. Maybe thats the problem. Is it hard to install a new valve?

Just so you don't feel lonely, I have the same problem. I'm also installing 1LE fronts as soon as I have a free weekend. I asked the same question probably 8 months ago, and most people think it's the the proportioning valve. It's hard to imagine how that thing can go wrong though, I probably don't understand how they work though.

Could well be. Those bigger and more efficient fronts are taking all the fluid (very basically) The Proportional valve effectively just apportions the fluid to wherever needs it. It isn't a big job to do, but having said that I have never done it myself.

Good luck I think we have found the problem. The 900 rpm may make a bit of a difference but the brakes should still hold. Try lowering your idle and see if that will at least get you your ticket.

Cheers,
Felix

i have an 88 iroc, factory 4 wheel discs.... my rears wont stop rolling either if the car is off the ground. all new brake parts too, rebuilt it all with the new motor that got tossed in the car in 2002. guess im not the only one.

im going to be upgrading to a complete aerospace components kit really soon. so i wont have to worry anymore. hehe.
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