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ongoing brake saga- update!


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1991 mj 4.0 4wd

replaced:

mc- 3 times (bench bled each time)

calipers (yes they are on the correct way, bleeders up)

wheel cylinders (shoes adjusted)

swapped to xj prop valve and eliminated rear valve

 

bled and bled with vaccuum bleeder and with a second person. bleeding is being done right and have been doing it for 15+ years.

the pedal feels ok when the truck is off. when started it goes to the floor when pushed slowly but when mashed, it feels ok. if you pump the pedal it also feels solid which seems like there is air in the lines.

when driving, if i mash on it, the pedal feels solid but does not stop all that quick. when pushed normal, the truck slows down but the pedal goes through the entire stroke fairly quickly.

should i take it in to get a pro to bleed it? running out of ideas here. i have gone through a few bottles of brake fluid

thanks

nathan

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get you some line clamps and clamp off each line one at a time starting at the rear. if the pedal gets hard like its supposed to like your talking about, then there is a prob some were in the rear. if not put it on the RF wheel. same thing. if not put it on the LF(all 3 hoses should be line clamped now). if the pedal is hard, master is good but if it still goes down its the master or prop. valve. are you using a new or used prop vavle?

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Did you disassemble and clean out the XJ combo valve before you installed it? What you describe sounds exactly like what my friend in PA went through -- with an XJ. He eliminated the stock combo valve entirely, put in a Wilwood adjustable proportioning valve in the line to the rear, and his problem went away.

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Did you disassemble and clean out the XJ combo valve before you installed it? What you describe sounds exactly like what my friend in PA went through -- with an XJ. He eliminated the stock combo valve entirely, put in a Wilwood adjustable proportioning valve in the line to the rear, and his problem went away.

i cleaned it but did not disassemble it. can they be taken apart and cleaned out? maybe i should just get the summit racing adj prop valve and try that.

nathan

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well to test the theory of the stuck prop valve, i replumbed around it. hooked the rear brake right up to the mc and used a splitter to go from the mc to the front calipers. bled the brakes and there was no change (besides being able to lock up the rear brakes at will).

something is up with the front brake circuit.

new calipers

new mc

pedal feels good when mashed or pumped. goes to the floor when pushed normal.

time for a 95xj mc and booster?

nathan

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I had the same problem with my YJ a few years back - it began when I swapped an aftermarket 4wheel disc brake master cyl. and brake booster... after countless hrs of bleeding installing and reinstalling my brake pedal was nice and soft untill I realized the brake lines were installed backwards at the master cyl. :wall: once we swapped them (front to back and back to front) it was all good!!!! good luck.

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have the rubber lines been replaced? they like to rot, and then they swell with the pressure, rather than transfering the pressure to the brakes.

?

no, the rubber lines have not been replaced. i can look into replacing the front lines but it would seem like mashing the pedal would not cause the pedal to feel ok if the lines were bad. they are pretty cheap though and i will replace them for good measure.

nathan

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well, i took apart the prop valve and made sure it was clean. looked good and everything moved like it should. put it back in and took out the mc and bench bled it again. did have some small bubbles come out of the front circuit. reinstalled everything and bled (no vaccuum pump this time). brakes feel the same as before. i think the mc may just be bad again?? i am not going to replace it unless i can get a 95 xj dual diaphram or swap to the wj one. this is driving me crazy as i want to start moding the mj but gotta get it to stop right first.

nathan

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  • 2 weeks later...

well i think i fixed the brakes, pretty major overhaul though. i swapped out the booster/mc with one from a 99 wj. it was as easy of a bolt in as could be. the brake rod was the same length as was the hole for the pedal. i used some washers to space out the booster from the firewall a little and did a little bending of some sheet metal. used the brake lines that came with the master and re-flared the ends to match the xj prop valve. bled the brakes and the pedal feels amazing, much better then when the jeep was new. i have just a little air trapped still but with a re-bleed with a buddy and the brakes will be dialed.

i picked up the booster/mc from ebay from a guy parting out a 99 wj for $50 shipped to my house. it also came with the abs unit which i am going to try and resell.

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got the idea from here-

http://www.4x4wire.com/jeep/tech/brakes ... /index.htm

i didn't have to do any of the pedal rod mods like he did though.

i will give an update in a few days.

nathan

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