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Old 11-19-2015, 02:21 PM   #1
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Default Help me brake my heep

2000 TJ, disc front drum rear.

Symptoms: rear drivers brake locks up, all other wheels stop normally.

Bled all 4 wheels, this fixed it for less than a day. Replaced 2 leaky rear wheel cylinders, bled all 4 again, problem still exists. Pedal feels firm when car is off. Kinda spongey when its on. But firms up towards the end of travel.

Bad prop valve? Air in prop valve? Bad master?

Going to try and bleed the prop valve tonight. Then order a new one.

New to jeeps, help plz.
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Old 11-19-2015, 03:07 PM   #2
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Bad booster or master is what it sounds like to me.

Check the gasket between the master cylinder and the booster.
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Old 11-19-2015, 03:11 PM   #3
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Why would a booster cause the locking up? I can order a master on rockauto, for $45.
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Old 11-19-2015, 03:59 PM   #4
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Is it a diagonal split with two prop valves or a F/R split like a Miata?

--Ian
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Old 11-19-2015, 04:08 PM   #5
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I overheated a drum on my Colorado and toasted a return spring enough that it wouldn't return on it's own. The fix was return springs, easy enough.

Torque of drag from toasted return spring would put the shoes in contact, then they cam up, out and lock up. At least that's what I figured was happening. With no line pressure the rear cylinder is soft and lets the top of the shoes go nuts.

Or they're adjusted too tight and are camming up, locking till there's absolutely no motion, or you hit the hat with a sledge really hard cussing about how you'd just like to go the **** home...

Drums suck.
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Old 11-19-2015, 04:09 PM   #6
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It's a combo valve. From what I can tell it's front straight through, rear proportioned.

http://www.rowand.net/Shop/Tech/imag...ationValve.jpg
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Old 11-19-2015, 05:09 PM   #7
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Quote:
Originally Posted by aidandj View Post
Why would a booster cause the locking up? I can order a master on rockauto, for $45.
I was thinking of the pedal feel problem.

In my experience when you have a firm pedal with the car off but a spongy pedal with lots of travel when the cars running, it's usually a problem with the master, booster, or the gasket in between them.

Doesn't explain the rear drum locking up...

Last edited by Efini~FC3S; 11-19-2015 at 05:11 PM. Reason: I haz dum
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Old 11-19-2015, 08:58 PM   #8
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Quote:
Originally Posted by aidandj View Post
It's a combo valve. From what I can tell it's front straight through, rear proportioned.

http://www.rowand.net/Shop/Tech/imag...ationValve.jpg
Huh, I totally don't understand what everything in that diagram does.

Anyhow, if the dual master is split to F/R like with the Miata, then you only need one prop valve and I would think a busted one would lock up both rear drums, not just one.

OTOH, if it's split diagonally, then you've got two prop valves and it could just a single one that's broken. The diagram appears to have two front outlets, though, so that seems unlikely to be the case.

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Old 11-19-2015, 11:41 PM   #9
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just as info-

its an F/R system with a hold off valve on the front circuit (for shoe take-up), proportioning (or limiting) circuit on the rear and an imbalance warning system. the front circuit also integrates a spliter. its much less complicated than it looks.


i still think its the master aidan, its the only thing that explains both symptoms.
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Old 11-19-2015, 11:51 PM   #10
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Get this.

A couple hard stops the problem goes away.

Car sits for 20 minutes. It comes back.

Going to try and drag the ebrake to see if heating the rears up is what fixed it.
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Old 11-20-2015, 12:04 AM   #11
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Drum brakes are evil voodoo. Rip them out and replace them with discs.

--Ian
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Old 11-20-2015, 09:11 AM   #12
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There are 2 solutions to fix this.
Swap in a 8.8 Ford rear from an Explorer. Easy swap, better axle with discs.
Or you can put in a Dana 44 (doubt you need the beef of a Dana 60). They were a factory option for the TJ so they are readily available.

Take this opportunity to swap gears and install some lockers.
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