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  1. #1
    Junior Member
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    Jul 2011
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    3

    comanche mj brake preportional valve

    i have a 1987 jeep comanche 4x4 with a 4.0l and aw4 transmission. i lifted the truck 5 inches in the front and 3 in the rear.

    when i first lifted it i moved the preportioning valve down 3" so it would work with the lift. this made the wheels lock up too quick. then i put it back to were it was when i started. the brakes work fine but they seem a little weak.

    does anybody know how to adjust this valve

  2. #2
    Junior Member
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    Jul 2011
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    I would find the sweet spot with the arm and duct tape it there. there are no adjustments procedures to the valve itself and no replacements available. if it's gone bad, the next step is to trash it and go with an aftermarket adjustable prop valve.

  3. #3
    Junior Member
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    Jul 2011
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    6
    remove the valve and replace it with a 'T' fitting. But then you won't have any proportioning. the front valve that looks like a prop valve is really just a splitter.
    -So you could remove the rear valve and splice in an aftermarket valve
    -Or you could remove the rear valve and swap in an XJ front valve up front (and with it, remove one of the rear lines in the MJ since the XJ only has one line running to the rear axle)

  4. #4
    Junior Member
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    Jul 2011
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    I did basically the same thing when I first got my MJ. There were two blown lines and the load sensing circuit was rusted beyond belief. I ended up taking the prop valve from my Cherokee that I had laying about and just put that in. You don't need to run new lines unless you want to, it fits right in (just ignore or remove the front linen as that's for the load sensing circuit).

    You will also have to bypass the T fitting right above the rear axle. If you don't, then this could cause a massive leak in the rear.

  5. #5
    Junior Member
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    Jul 2011
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    i removed mine but i didnt add a xj valve and i think they work great.

  6. #6
    Junior Member
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    Jul 2011
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    did the prop valve in a cherokee change at all in any years or will any xj valve work. cause some companys only sell the 84- 86 prop valve

  7. #7
    Junior Member
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    Jul 2011
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    6
    I'm running off memory here so I might be wrong but...I believe the did change it from '86-'87 with different valving. When I ripped into my '92 MJ, I had the regular sized Cherokee brakes. But when I ripped into my '86 Comanche, I had the thinner brake shoes. Besides this '86, I haven't seen these thinner shoes on any other XJ or MJ that I've had (I've owned a '90 XJ, '92 XJ, and '92 MJ with all the same rear brake shoes).

  8. #8
    Junior Member
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    Jul 2011
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    4
    One thing I did that I now regret is I put the rear wheel cylinders for an AMC Eagle in (because they are a bigger bore for more rear braking) THEN I discovered my rear brakes had no pressure (after driving for almost a year) because the rear valve was shot AND the brake line was rotted through! (only rust on the whole truck!) I bought a line adapter (7543 IIRC?) and screwed the original front to back line direct to the brake hose and capped the other line at the front.
    Now I can lock them up TOO easily, even with 33" tires if I don't have weight in the back. Adjustable prop valve AFTER I finish the double booster swap!

  9. #9
    Junior Member
    Join Date
    Jul 2011
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    5
    If you're going full custom, do away with the proportioning valve, load sensor, etc. Run your front line from the MC down to the brakes with a simple "T". Put an adjustable valve on the rear line, and adjust it so the rears don't lock up. If you're putting an adjustable in anyway, there's no need to keep the factory valve. Only down side is, the brake light on the dash won't work as a warning system in the case of a partial system failure.

  10. #10
    Junior Member
    Join Date
    Jul 2011
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    5
    In the FSM there is a procedure for setting the angle of the lever on the rear valve for proper operation. It would seem that if the angle were set correctly, your lift wouldn't be an issue as long as the rod was lengthened to compensate for the lift.


 
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