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Comanchee 2 wheel drive Brakes


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I am hoping one of you comanchee addicts can help us out. My son has a 1990 2 wd comanchee with the 4.0L in a long bed version. This truck sat for a long time before he got it, and it was a real rust case. Any ways he got a notice to take it for an emissions test. He was told at the test that they could not test it cause the rear brakes are not working and they could not slow the truck down on the Dyno that the emissions people use here in Illinois. since then he has replaced many of the brake lines, put in new rear wheel cylinders, a new master cylinder and the proportion valve in the front. It has been bled has a rock hard pedal and seems to drive and stop great. He has now been back and they are still telling him that the rear brakes are not functioning properly. Is there something unique to this truck that he and I do not know about? The only thing he has not replaced is that rod thing on the rear axle that goes from the frame down to the rear axel. I do not even know what this does. Does it work like a proportioning vave? Can it be bypassed?

 

Please let us know if you have experienced this or know what to do to get this bad boy back on the road.

 

Thanks

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That rod is a hydraulic switch or metering valve that controls the brakes when there is a load in the back.

 

My advice because that thing is made of unobtainium is to route a line to bypass it and then remove it from the truck...they will never know and if they do, then you have the part already removed for possible rebuild (if it can be in fact, rebuilt)

 

Wayne S

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it's got to be the rear prop valve, remove it and modify the orignal MJ valve or swap in a XJ one to get rid of the dual brakelines that run to the rear.

 

i just removed mine and used a XJ prop valve. here is some good reading about it check it out.

http://www.naxja.org/forum/showthread.php?t=81438

http://comancheclub.com/forums/viewtopi ... ning+valve

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YUP, That is the proportioning valve. That rod is how it actuates. as weight is added to the bed the rear brake bias is increased giving you MORE rear brakes. with out weight the front brakes do MOST of the work.

 

It COULD be as simple as adding weight to the bed for these tests!!

 

An MJ does NOT HAVE a prop valve up front. What you see is a metering/ distribution bloc. Its purpose is the split the lines and work with the dash brake light. It does isolate the brakes in case of a line blow out. Where that to happen you will retain brakes to the other axle.

 

You CAN just remove it, re-plumb a line from the distribution block to the rear line and call it good. You can also do that and replace the distribution block with a proportioning valve from a Cherokee XJ and call it good.

 

I ran with the first option for some time with ZERO problems. People told me the back would lock up first making hard stops unsafe. Well I have been driving PU's for 20+ years and the ALL lock up the rear first!!!

 

Personally, I would throw 500 lbs in the bed and go take the test. its likely the rear valve is working as you say the peddle is hard and jeep stops well.

 

CW

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The above posts have covered it pretty well. As noted, the front "thingie" on the MJ is not a proportioning valve, it's just a distribution block with the brake system warning plunger switch in it. That thing in the back that the rod goes to from the differential is the proportioning valve.

 

I recommend eliminating the rear proportioning valve. The one on my '88 BLEW OUT when I had to make a panic stop. That, as they say, is not a good thing. And the idea of swapping in a Cherokee front proportioning valve sounds great in theory (it is a bolt-in swap), but the reality is that the Cherokee proportioning valves are notorious for getting gummed up and resulting in ... no rear brakes.

 

IMHO, I favor just eliminating the circuit that runs to the rear proportioning valve. Plug the outlet on the front bottom of the stock MJ metering block, and run a new line directly from the outlet in the "nose" of the block directly to the rear axle. Yes, it will possibly cause early rear wheel lock-up in a panic situation, but at least you'll have rear brakes. You can alleviate that to an extent by using rear wheel cylinders with a smaller diameter piston.

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