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Discussion Starter #1
Hey guys, I could use a little help here... lol. I am having a serious issue with my front left caliper locking up when I stand on the brakes. I have tried 3 master cylinders, 2 boosters, 3 sets of Cobra calipers, and I also tried bleeding the brakes with a pressure bleeder, and also with the conventional foot method. Nothing I do fixes the problem.

The last things I can think of ...

kinked hard line?
rear calipers?

The pressure bleed holds steady at 15psi so I'm fairly confident there are no leaks. The master cylinders were bench bled in a vice and there are no air bubbles coming out from any of the calipers...
 

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The only tip I can offer for bleeding stubborn brakes is to rap on each caliper as you're bleeding it with a mallet to dislodge any trapped air bubbles. I can't remember where I picked it up but it can't hurt, right?
 

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Discussion Starter #3
Hey at this point I am willing to try anything... thanks. I'm going to swap the rear calipers here shortly, will report back with results. I'll tap the front and rear calipers with a rubber mallet when I bleed them.
 

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What's left inside your factory proportioning valve?
 

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His car has my front calipers rear calipers gutted prop valve and master on it right now. When I had all that stuff on my car it stopped really really good had some track days with it never any problems. We put the rear calipers on so only thing I can think of maybe is a kinked line at this point.. Or is it normal for the left front to lock up first? The only difference from the 2 cars besides the hard line is that I used the factory 5.0 booster and he has a 93 cobra booster.
 

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Is there any Chance you could get a pressure gage on each wheel (in particular the fronts)? Ideally, you would have two gages so that you could read them at the same time, but I am sure that checking one at a time would also work.

Have you swapped the front soft lines? Is there any chance that the right one could be restricting flow?

Have you talked to Jack?

Good luck.


--Vince
 

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I've had front lines cause similar issues also, they can almost act as a check valve, pressure will push them open, but when the pressure is released, they collapse.
 

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That's a good reason for brakes to drag, but it doesn't affect the input pressure and therefore doesn't affect one locking up early.
 

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Mine does the same thing. I have the cobra fronts with rear drums.
 

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Could something be causing the outside pad to set to close to rotor when the brakes arent beint applied then once you hit the brake there is less air gap in that side possibly. I know i have taken new bearing hubs from different manufactures and set them side by side and they are different heights. Just a thought.
 

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There's a thread here or cc-com that talks about how it's common for one of the fronts to lock up early, but I thought it was the right side, and I'll be damned if I can find it anyway.
 

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Discussion Starter #14
Could something be causing the outside pad to set to close to rotor when the brakes arent beint applied then once you hit the brake there is less air gap in that side possibly. I know i have taken new bearing hubs from different manufactures and set them side by side and they are different heights. Just a thought.
The car has new Timken hubs on it... which I know many people on this board and over on c-c have used as well. However, I was having the same issue way back when I had untouched 94-95 spindles and Ford hubs, so I'm quite confident that the hubs aren't the problem. I definitely appreciate the insight.

I can't imagine it could be a bad Wilwood valve? I think before anything, my task should be to get a gauge on each caliper and see what the reading is. Will do that tonight (my friend has access to one) and report back.

Very exasperating given that I can drive this car anywhere and the brakes work great around town, yet I've got all these fancy suspension do-da's done and the car is completely not track safe because of the lock-up issue. :livid:
 

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I agree. I would corner weight the car. Most Fox Mustangs will have about 100lbs of extra weight on the LF tire. With you in the car, adjust any spring perches to get the diagonal weights as equal as possible.

To test the behavior of the brake system, put the front end in the air with a jack. Depress the brake pedal 10 or so times to get rid of any vacuum in the power booster. Place a weight on the brake pedal, that can't fall of or move. Put a torque wrench on the LF wheel stud that is at the top of the wheel. You will need a beam style for this. Put the torque wrench parallel to the ground. Push down to see how much torque it takes to move the wheel. Repeat for the RF side of the car. You may need to adjust the weight that is placed on the brake pedal. If the torque for the left and right side of the car is the same, then you probably have some problem with the corner weights.
 

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so we did what you said jack with the tq wrench and the passenger side took 20 more ftlbs than the drivers side and the drivers side is the one locking up. doesnt make any sense to me?
 

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Discussion Starter #19
~30 ft/lbs driver's side, ~50 ft/lbs on the passenger side. Done with me sitting in the car maintaining consistent brake pressure, Matt using a Matco beam-type torque wrench and turning the wheels.
 

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I did it basically how you would set pinion pre load in a rear end constantly turned the wheel and he put the resistance on it we did it several times and each time passenger side was 20 ftlbs more.
 
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