XJ Brake Upgrade (Continued frustration)

chris

chris

cltdba
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Joined
Sep 28, 2009
Location
Concord, NC
For history, please read this thread: http://www.nc4x4.com/forums/showthread.php?t=83400&highlight=brake+frustration

So since that thread, I have swapped in an 8.8. I had hoped the new disc brakes would magically fix my problem. WRONG! The jeep is up on jack stands with tires mounted. With the vehicle in drive and standing on the breaks with all 250 lbs of my body plus whatever force I can apply by trying to relocate the front seat to the rear will not stop the rear tires! There are no leaks in the brake lines anywhere and we get plenty of fluid with no air at all the calipers.

So, last night we took apart the proportioning valve. Cleaned the crap out of it and put it back together without the o-ring and bled it. Doing this is supposed to allow more pressure to go to the rear brakes. Well that had no effect whatsoever. We noticed a hissing sound coming from around the power booster where it mates to the master cylinder. Took off the master cylinder, removed the rubber seal on the booster, cleaned it, cleaned around the booster, and even ran some black RTV around the master cylinder. Buttoned everything back up and no more hissing sounds, but still no brakes.

You can get very hard stiff pedal with the jeep off and when you crank it while holding the pedal it does soften up so that tells me the power booster is okay. Could it be that my new master cylinder is faulty? Is it the proportioning valve? There's not much to that thing, how could it be bad?

My next thought is to upgrade to a double diaphragm booster and a newer master cylinder. This is where I need some advice. I've read several articles and from what I understand you can run a 95/96 booster/mc from an XJ and will only need to drill out the rod hole a bit. I've also heard that the WJ booster/mc combo works as well. Additionally, I read that I should grab the proportioning valve internals out of a 4-wheel disc ZJ and swap them into mine.

Has anyone done these upgrade? Which one works better and is the easiest? Are there other options? I'm just going to go buy the parts new from O'reily instead of dicking around with junk yards. I'm tired of this problem and I want it fixed. I'm not looking for 18-wheeler brakes but it would be nice to actually stop the jeep.

HELP!
 
Have you driven it since redoing all that stuff? If so, does it not stop well? Most of my vehicles will overcome the rear brakes in 2Hi with the brakes pushed as hard as possible and a fair amount of throttle.
 
dont know about xj's but i know with some of the chevy cars that people put the camaro disks in the back of they end up having to use the camaro master cylinder. i think its something about the disk caliper needing more volume of fluid than a drum set up master cylinder can give.
 
jeepinmatt said:
Have you driven it since redoing all that stuff? If so, does it not stop well? Most of my vehicles will overcome the rear brakes in 2Hi with the brakes pushed as hard as possible and a fair amount of throttle.
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Does it count as driving it if the wheels weren't on the ground? The thing is I can spin the wheels in drive and then put it in neutral and press as hard as I can and they just keep spinning. If I pump and pump I can see them grab a little bit and slow down, but they never stop until gravity doesn't it's thing.

By the way, front axle works great! It didn't break when we bound the brakes up! hahahah Thanks again for your help.
 
malibu79 said:
dont know about xj's but i know with some of the chevy cars that people put the camaro disks in the back of they end up having to use the camaro master cylinder. i think its something about the disk caliper needing more volume of fluid than a drum set up master cylinder can give.
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Yeah I thought about that too. Supposedly the stock XJ master cylinder and stuff will work with the disc brakes from a ZJ, but they recommend upgrading it. Haven't found anything on the 8.8, but I suspect that I do need a bigger MC which is why I'm contemplating upgrading. The WJ is more work, but I think it was designed for 4 wheel disc. Not sure on the 96 XJ. Perhaps it was?
 
cltdba said:
Does it count as driving it if the wheels weren't on the ground? The thing is I can spin the wheels in drive and then put it in neutral and press as hard as I can and they just keep spinning. If I pump and pump I can see them grab a little bit and slow down, but they never stop until gravity doesn't it's thing.

By the way, front axle works great! It didn't break when we bound the brakes up! hahahah Thanks again for your help.
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In neutral they should stop as soon as you hit the brakes. Definitely a fluid supply problem, though it could be flow or pressure. If there is any pressure at all, it should stop the wheels in neutral, but if there isn't enough fluid movement, the pads won't contact the discs. Even if there was air in the system, the pads should still push out enough, they just wouldn't create good feel or enough pressure to stop it in drive.
 
So what do you think is wrong with it? Do you think upgrading MC and PB will fix it? Could the prop valve actually be bad? What if I take the spring out, would that help? lol? What if I take the whole dang valve out and apply 50/50. :p
 
Sounds like maybe a kink in the line to the rear brakes,

I swapped an 8.8 into my TJ pulled the o ring from the prop valve and it has great brakes. Did you use the ford calipers?

Also I have seen them installed upside down before, IE driver on passenger and vise versa
 
Yes, it's Ford calipers. It's the original calipers in fact. There are no kinks in my line. That line is one sexy SOB! I'll have to take some pics of my fantastic brake line bending job. When bleeding I get fluid out of both rear calipers. My front brakes work though I'd expect them to have a bit more stopping power, but with 4.56 gears I don't doubt my right foot is able to overcome the front brakes. Either way the fronts hold well enough for my needs.

By the way, the TJ has a much better braking system than the XJ.
 
Are the calipers on backwards? make sure your bleeder valve is higher than the brake line cause that sounds like the same problem I was having.
 
Are the calipers on backwards? make sure your bleeder valve is higher than the brake line cause that sounds like the same problem I was having.
 
Hmm, not sure if they're on backwards. I'll check the bleeder valve tonight. Thanks, I didn't know how to tell if they were on backwards.
 
If you have the original calipers have you applied pressure with them off to see if the pistons move. I only had rear brakes when I put my 44 in the front because the front calipers were stuck. But my rear disk brakes work really good with the stock 88' master cylinder.
 
The 96 booset and mc should be bolt in. One of the guys I wheel with did it to his MJ and all he did was bolt it in. If you are having brake troubles with a new MC then its either a blead problem or a caliper problem.
 
I'm still saying the calipers are stuck. If you bleed the brakes and have good fluid and good pedal preasure but no brakes then I would think that the pistons aren't moving the pads to apply preasure on the rotor. Probably need new calipers.
 
KrawlDaddy520 said:
I'm still saying the calipers are stuck. If you bleed the brakes and have good fluid and good pedal preasure but no brakes then I would think that the pistons aren't moving the pads to apply preasure on the rotor. Probably need new calipers.
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You could remove the calipers and use a c-clap to compres them. Then remove said clamp and press the bakes. If the piston move you know you got movement. Be carefull to not shot the piston across the shop though. :popcorn: when I say remove the clamp I meant loosen it.
 
I'll be heading to the shop later tonight and will give this stuff a whirl. Gonna go ahead and buy the new MC, PB and calipers. If calipers are good then I'll just return them.
 
When I had my old YJ, I did the 8.8 swap with 4.88 gears and 33s. It wouldn't stop worth a crap. I swapped in a MC from an E350 van, and got rid of the prop. valve. It worked better, but I could never get it to lock up the wheels. Looking back on it I should have swapped out the calipers too. I don't have that jeep anymore.
by the way, the E350 MC was almost a direct bolt in, I had to grind off just a little bit of the edge of the mounting ears.
 
I assume you used a power booster with the E350 MC, did you keep the stock single diaphragm?


Had Micky look at the calipers and he said the bleeder screws were at the bottom below the brake lines. So that tells me we have them on the wrong sides. He's going to switch them and try that again. I'm stuck here at work. :( What a great friend! :)
 
cltdba said:
I assume you used a power booster with the E350 MC, did you keep the stock single diaphragm?


Had Micky look at the calipers and he said the bleeder screws were at the bottom below the brake lines. So that tells me we have them on the wrong sides. He's going to switch them and try that again. I'm stuck here at work. :( What a great friend! :)
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I bet that is your problem, It will not get all the air out of the lines that way, Holds an Air pocket.
 
Here is one installed correctly

awww.nwjeepn.com_images_Axle_IMG_5396.jpg
 
Thanks for the pic. Hard to say what mine looks like since I'm not there, but looks like the bleeder is definitely above the hose in that pic. So if mine is below it then I've got them on wrong. God I hope this fixes the problem!
 
I must have gotten lucky on mine, cause I didn't even check when i put them back on. I pulled the when I was setting it up and put them in a box, then threw them on. I guess I was lucky or there upside down and I didn't notice the loss in braking, I remember it being a bitch to bleed.
 
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