prop valve - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 5 Old 05-12-2011, 10:23 AM Thread Starter
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Unhappy prop valve

Guys I'm trying to fix a brake issue I'm having with my 91 Mustang after I come off the track. The brakes drag bad..... to the point that the car will come to a stop on its own after I let off the gas.

Thanks to the folks from Corral that are helping me fine the problem.

The prop valve was one of the items a fellow corral member said could be the problem. The heat from the LTH is within 1/2 inch of this valve. So before I spend hours and money moving the valve or just removing it from the brake system I hoped for more feedback from the AI/AIX guys.

Last week at the track I know I saw at least two AI/AIX cars with the valve in place with LTH. Of course I don't know if they were having any issues with their brakes but by the way their cars were hauling butt, I don't think so.

Again just trying to see if anyone has had brake dragging issues and they found it to be the prop valve next to their headers????


91 GT
349 A-4
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post #2 of 5 Old 05-12-2011, 12:54 PM
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The next time this happens, loosen the MC off the brake booster by 3 full turns of each nut. Pull the MC out against the nuts, and see if the brakes are still dragging. If not, you know you have to shorten the booster rod and it's nothing to do with the PV.

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post #3 of 5 Old 05-14-2011, 11:19 AM Thread Starter
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MFE, I've tried that at the track....I took the M\C completely off the booster and still the brakes were locked up. Couldn't turm them by hand. Of course I could crank the engine put the car in gear and turn the wheels but as soon as you let off the gas the car would stop on its own. Half hour later, they were fine. I tend to agree that the issue is a heat problem. Could changing out brake fluid help? I'm using DOT 4 right now. Yes I know that high price stuff would be better but I'm not cooking the brakes that much yet I guess it's worth a try to change out the fluid for that 580 stuff, wrap the headers on that side and add more heat shields. If that doesn't fix it I'm back to a bad brake line!!!

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post #4 of 5 Old 05-14-2011, 08:26 PM
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When was the last time you rebuilt the brake calipers? Are you using floating calipers? Seals that are old or heat baked can cause the caliper pistons to stick. The calipers could be cocked on their slides.

"Drag racing is for those people who don't know how to down shift and brake at the same time. "
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post #5 of 5 Old 05-16-2011, 09:45 AM Thread Starter
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All four calipers have less than 200 miles on them. I did replace the rear piston seals last year. I had just completed a dyno pull, got out of the car and the left rear brake was smoking. Looking closer I found that brake fluid that been thrown all over the wheel and under carridge of the car causing the smoke. So I replaced all the piston seals in the back brakes. I've had the car out after that with no issues of the brakes locking or dragging but two weeks ago was the first time I had really punished the barkes and replacing the seals.

If a piston was not seeding correctly on the seal would it not do that all the time? Would a great amount heat have to be introduced before the issue would appear?

I will pull the calipers when I get a chance but the first course of action I think is to heat up the brake really good and see first of all if my rewrap of the headers by the prop valve helped. If the brakes are dragging/locked, next would be to open a bleeder to see if pressure is still in the line. If that is not the case then the rear calipers will come off to check to pistion seals ect....

Thanks for the information

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