Comanche brake system

I know performance brakes have been discussed here at length, but I've got a unique problem applying this to my MJ. As you may be aware, Comanches have a brake proportioning system attached to the rear differential to adjust for various bed loads. What this presents me with is a proportioning valve that's different (extra line) than those on XJ/WJ Jeeps. My goal is to outfit this "new" truck with the best brakes that I logically can. I'll be swapping an Explorer 8.8 (with factory discs) into the rear and upgrading to WJ brakes in the front. The plan is to use a late model XJ booster ('99), but I'm getting hung up on the proportioning valve. Do I modify the MJ valve for rear discs, or just bail on the whole "self adjusting" feature and use something else? It's a short bed MJ, so it's unlikely that it will ever see a lot of extra weight riding around back there. Any thoughts?

Since you are changing almost everything else out, why not use a ZJ or WJ proportioning valve instead of the MJ one? It eliminates the extra line going to the rear and the load sensing valve. I bypassed the one on my '87 longbed with no ill effects... I essentially replaced the valve with a tee, leaving everything else as it was.

Since I'm not dragging around a pile of concrete blocks, I'm inclined to ditch the adjuster and just move on. No difference, huh? That helps. Thanks.

Wilwood adjustable proportioning valve is supposed to work well. I have one waiting to go on along with a '96 booster. Just an FYI, the 96 booster doesn't need a rod swap, a '99 would. I would NOT lose rear adjustability all together unless you're going to have 33-35 inch tires or be hauling max payload 100% of the time. The last (oh and I do mean last) shop that worked on my MJ thought it would be a good idea to cut the load sensing valve and tie it up to full pressure. What an unpleasant PIA that made it to drive around. Just touching the brakes would about send you through the windshield and it was impossible to drive on wet/snowy roads. Alternately, a XJ/ZJ/TJ/WJ prop valve would work since they also function as metering valves unlike the MJ. The only downside to that is you'd lose the ability to up the rear braking power as loads/tires/whatever called for.

ditch it and forget about it, it's nothing but trouble!

Like Lawn 'Cher and CheapXJ, I vote to scrap it.

I also have a shortbed MJ. Popped a rear line in a panic stop when some idiot cut me off a few weeks back. Replaced the busted line in a friend's garage one rainy afternoon. Being the purist that I am, I disregarded Lawn 'Cher's suggestion to eliminate the rear proportionaing valve. I wanted to keep everything "original."

Started to bleed, found another ruptured section, replaced that , started to bleed again. I was pushing the peddle, my friend was under the truck with the wrench on the bleed screw.

"Oh, s*&t" I hear. He got a face full of brake fluid, pouring out of the body of the proportioning valve itself. Hmmm. Dealer was right up the street. New valve = $90+ with my discount. No brainer. We capped the line and proceeded from there.

The effect of dumping that rear valve is maximum braking to the rear brakes. If -- and I emphasize "IF" -- you find the rear brakes consistently locking up before the fronts, you can either fit smaller rear wheel cylinders, or add a Wilwood proportioning valve to compensate. More than likely, no compensation will be needed.

just swap in an XJ valve, eliminate the return line (or leave it under there... comes in handy for trail spares ) and then run the feed line directly to the rear brakes.

never once had any trouble hauling heavy loads or locking up the rear wheels in the rain.

Eagle said:

We capped the line and proceeded from there.

Click to expand...

How? I'm about to do the same thing. How did you just cap it off? Also, which line is which?

It's funny how that little voice in the back of your head oftens seems to have the correct answer. I'm going to eliminate the rear valve. If it's not back there, it can't break!
Anyone here currently using the Wilwood valve? Would you do it again?

JnJ said:

How? I'm about to do the same thing. How did you just cap it off? Also, which line is which?

Click to expand...

John,
You need to cap the return line port on the prop valve under the MC. There are two ports on the bottom of the valve, the return one is the one in the front. You can cut the line somewhere and cap it with a compression fitting, or unscrew it at the valve and cap it there (it's pretty tight working conditions unless you take out a bunch o' crap first). IIRC, the port is 3/16".
Jeff



HTH,
Jeff

I'll tell you how I like the wilwood valve in a couple of weeks. I do know that with the prop valve tied up, there was WAYYYYYYYY to much rear braking force. That may be a function of having a 44 with the big brakes, but it was almost undrivable. I just find it had to believe that you guys have no problem running full pressure to the rear all the time. Maybe I'm just different...

CHW in the NAC put in a Wilwood valve last year. Even with the larger Dana 44 rear drums and wheel cylinders he was getting lousy braking and a soft peddle that repeated bleeding could not eliminate. He finally took out the stock combo valve (this was on an XJ, not an MJ) and re-plumbed the entire system, with a Wilwood in the rear circuit. Once he got it dialed in, he said his brakes were better than they had ever been.

I've used the Wilwood valve on street cars and appreciate the difference they can make, but didn't have any experience with them on Jeeps. From what I see here, it seems like a good bet. Thanks!