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Rear porportional valve


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I haven't, but my friend has. This is a standard (adjustable) proportioning valve, it is NOT in any way height or load sensitive. This is a Mopar part but it looks identical to (and probably is identical to) the Wilwood adjustable proportioning valve I have mentioned in previous discussions. I have removed the rear proportioning valve from my '88 MJ and I don't feel any need for reducing the rear braking, but if I did ... this is what I'd use.

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junkyard run.

 

cherokee distribution block from cherokee.

 

remove comanche distribution block.

 

remove comanche brake line that runs from load sensing valve to the front of the block.

 

replace rear brake sending line (front lower of block) if needed. bypass load sensing valve, connect straight to rear brake hose.

 

reconnect.

 

bleed all brakes.

 

done. you now have 60% front brakes, 40% rear. and you don't have a POS oem weight valve.

 

 

the distribution block (xj prop valve) is located under the brake booster. they are almost directly interchangeable.

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junkyard run.

 

cherokee distribution block from cherokee.

I don't recommend this, but IF you elect to do it ... before installing the XJ proportioning valve in the MJ be sure to open it up and thoroughly clean out the inside. The XJ proportioning valve is known to get clogged up and leave you with NO rear brakes. I'm facing that on my '88 XJ right now, and my plan is to open it up and disable the proportioning function entirely. I would much prefer to have too much braking than none.

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why wouldn't you recommend that? I've done it on every single MJ I've ever registered. not one has had failed brakes caused by this.

I don't recommend it for the reason I stated: The XJ proportioning valve is prone to clogging internally and leaving you with NO rear brakes. My '88 XJ right now (as of last winter) will not lock the rear wheels if I slam on the brakes on packed snow. Same thing happened to a NAXJA friend in PA, and I've read posts by other XJ owners with the same problem.

 

I have an XJ proportioning valve (the one I cut in half to see how it differed from the MJ distribution block) that came from a wrecked XJ. When I opened it up, I found that the internal spring and O-ring had been removed and the plunger had been set in the fully-forward position ... resulting in no proportioning. I have no way of knowing who did the mod or why, but the vehicle itself was stock, so it wasn't because of a conversion to rear disks. My best guess, then, is that he had no rear brakes and decided he'd like to be able to stop the vehicle. That's the best way to do it.

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I bypassed the load valve in the back of mine and went to larger wheel cylinders for increased brakes (I had planned on ZJ front brakes, which I still have)

Lockup on wet highway took a little getting used to

Premature rear wheel lockup is a possibility if you just bypass the rear proportioning valve and keep the MJ front distribution block. I can deal with that -- I'm old enough to have grown up decades before they started using proportioning valves, and I'd rather deal with too much rear braking than none.

 

For those who remove the rear proportioning valve and then have problems with rear wheel lockup, THAT's when you look at the Mopar/Wilwood adjustable proportioning valve.

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