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Discussion Starter #1
Anyone ever have a problem with their rear brake hydraulics not working?

When I am in the mud or snow and hit the brakes, the fronts lock and the rears do nothing. I even had a buddy watch as I repeated several times and then watched him do the same. The weird part is when it's in 4wd they all seem to work ok. This was done several times on the same path of snow/ice. The fronts act like skies and the rears just push on idle.

My rear brakes are adjusted and hold and release great, I changed the master cylinder and bleed them out very well. The previous owner showed me a receipt for rear brake cylinders and shoes installed recently.

The only thing I can come up with is the proportioning valve.
 

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Are they drum breaks? If so they tend not to work great when they get mud or water in them
 

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Could be the proportioning valve.
Take it to Midas and have them check the system. Sometimes it's free.
 

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Do you have an auto or manual transmission? I've had that problem on snow covered roads with the auto in my pick-up. I usually shift to neutral when trying to stop, seems the rear drive wheels want to push the front when it's slippery.
 

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Discussion Starter #5
Yes it is an auto. That is exactly what I do to stop.

I may just order an aftermarket adjustable proportioning valve. I don't think I can handle Midas trying to sell me everything under the sun.
 

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Sounds like a normal issue. Since some 70% of your braking power is in the front, the rears tend to be lightly braked by comparison. If you want you can remove the wheel and get to tweaking the drums so that the drum spins just freely, and all it takes is a little brake lever moment to stop them.

4WD braking works better because the braking force from the front gets transfered through the drivetrain to the rear, since all 4 wheels are locked together in the center.
 

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Theoretically yes. But without lockers front and rear you do not have four wheel drive, you only have one in front and one in the rear.
But I see where you are going with this.
 

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^When both wheels are under full traction on each axle, then it is a true 4wd system. However, the moment you begin to lose traction to one wheel, all bets are off. For the most part though, the theory does work.
 

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Discussion Starter #10
Solved the rear brake issue!

I put in a proportioning valve off of a foxbody mustang. Had to do a little fab work with the bracket but it all worked fine.

Brakes seem to work front and back really well. Just need to get into some real slick spots for the real test.
 

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Good. Keep us posted in case somebody else has the same issue.
 

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This appears to be a remarkably common problem with solutions all over the park. In my own case, an '08 Wrangler JKU, I had to have both rear calipers AND rotors replaced due to them seizing for no apparent reason at just under 50K miles on a JK. Now, about 3K miles later, the same thing is happening to my right front caliper. Interestingly, when I turn off ESP and let the caliper cool down, the issue goes away--at least temporarily.

It leads me to suspect either the ESP computer or the sensors that trigger the anti-rollover mitigation circuits. I'm asking if anyone here can clarify the issue as while I'm well aware of how easy it is for electronic circuits to break down under highly variable weather conditions, I don't have enough experience actually working on my Jeep to feel confident in performing a permanent ESP shutdown.
 
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