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Old 09-21-2012, 09:14 AM   #1
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What would cause brakes to lock up?

I had my car at the track a few weeks ago, I was on a pass and could feel the car slow up and could hear the motor was under a load. I knew something was up cause the car usually traps 6,500 rpms and this pass it went through around 6,200. As soon as I crossed the stripe, I let off the throttle, I hadn't even hit the brake pedal and the car was slowing way down, I had to down shift to second and give it throttle just to get it up to speed. By the time I had for my slip and was heading back to the trailer I had it in 1st gear around 1/2 throttle just to get it to move.

When I got to the trailer all you could smell was burning brakes, i walked around the car and touched all 4 wheels and all of them would burn the tips of your fingers.

I loaded it up on the trailer and took it home.

When I got home, I unloaded the car to put it into the garage the brakes had freed up, came of the trailer fine, and went into the garage fine.

The only 2 things I noticed was the MC was empty and i saw a leak line leak in the rear.

I am running 94/95 brake booster and master cylinder, 94/95 spindles, PBR dual piston calipers, on the rear I am running north race car brackets with 94/95 calipers and rotors.

Gutted stock proportioning valve, and a ford racing proportioning valve for the rear brakes.
I run wilwood brake fluid.

What would cause that? Do you think the leak caused it? Is there something in the MC that would cause it to lock up all 4 wheels when it gets low on fluid?

I'm going to work on it tonight or tomorrow. I'm going to fix the leak, top it off with fluid, and bleed the brakes.

What else should I look at?

Also, I popped the vac line off the booster, no fluid ran out.

Give me some ideas.
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Old 09-21-2012, 04:53 PM   #2
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The leak definitely cause it. If it was just one brake lock up then I would say its a bad caliper, but since all of them locked up then I will say its the lack of fluid.

I can't explain why, but I had it happen to me. Refilled the MC, and all was good.
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Old 09-21-2012, 08:03 PM   #3
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That's what I'm going to try. I mean if the parts were old then I would say bad MC or bad BB, but both are a year or two old. Both front calipers are new as well. The rears are used, but seem to be ok.

I'm going to fix the leak, rebleed, then take it to the track Sunday.
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Old 05-03-2013, 11:46 PM   #4
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just wondering if you ever had any more problems like this? or what the fix was? I just swapped to manual brakes for a coyote swap and twice have had this issue. After several miles into a drive it seems that the front calipers slowly get tighter and tighter until the car wont move. If I crack open a line at the master cylinder all is good for a while.

After I installed the manual setup I bled the brakes but later found I had a couple small leaks at the fittings. Master has stayed full though. Could that have let air into the system and now causing this issue?
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Old 05-04-2013, 11:59 AM   #5
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Sure sounds EXACTLY like what happens when the booster rod in the MC is adjusted too long. Back the nuts that hold the MC to the booster out 1 full turn and see if it improves.
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Old 05-04-2013, 08:04 PM   #6
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dont have a booster, it's a manual brake setup from MM.
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Old 05-04-2013, 08:05 PM   #7
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Good thread. My car is hard to push around the driveway. Has cobra everything. I thought about the pushrod deal after reading about that on CC.com

@MFE, in regards to Gilroy and the Coyote swap poster, wouldn't the brakes just be locked up all the time? Not second guessing, cause I wanna know too! ;-)
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Old 05-05-2013, 12:25 AM   #8
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No, it's like riding them slightly. They get hotter and hotter, the rotors and pads expand, and soon it won't roll at all. Been there, done that.
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Old 05-05-2013, 10:14 AM   #9
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Even without a booster, I guess the rod could be too long and applying constant pressure on the master. I did notice after the install that the pedal arm seemed to be pushed back tight against the steering colum bracket. Gonna go check it out.
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Old 05-05-2013, 11:08 AM   #10
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okay, the rod is definately too long. It was even at its shortest capability. I'm gonna try cutting off about 1/4 inch off the rod end bulb and reshaping it. The I'll get it back out on the road and retest.
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Old 05-06-2013, 10:09 PM   #11
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MFE, Thanks for pointing me in the right direction! Finally got the rod short enough and the calipers are no longer "sticking".
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Old 05-15-2013, 08:17 PM   #12
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Quote:
Originally Posted by 87coupe50 View Post
just wondering if you ever had any more problems like this? or what the fix was? I just swapped to manual brakes for a coyote swap and twice have had this issue. After several miles into a drive it seems that the front calipers slowly get tighter and tighter until the car wont move. If I crack open a line at the master cylinder all is good for a while.

After I installed the manual setup I bled the brakes but later found I had a couple small leaks at the fittings. Master has stayed full though. Could that have let air into the system and now causing this issue?


all i did was add brake fluid and i never had the issue again...
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302 1.59 60' 7.63@88.19 12.06@110.58
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