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Unread 09-15-2013, 03:58 PM   #1
mightymulhern
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XJ Brakes, Rear Discs + Dodge 2500 MC, Not so good

Ok folks. I've spent a lot of time reading posts which is how I got to where I am not. At this point though, I'm going to punt and ask for suggestions.

I've got a `98 Cherokee XJ. Last summer I added the Crown rear disc brake which basically is calipers/rotors from a `97 Grand Caravan. This addition took my poor braking performance and turned it into poor braking performance with a very mushy pedal. I actually had a mechanic install the kit so I assume it was done right. It was however a step down in performance.

Recently I noticed the rubber lines in back had started cracking so I replaced the hard lines along the axle and the rubber lines to the rear calipers. While doing that, I also swapped in a master cylinder from a Dodge Ram 2500 which has a 1.25" bore as opposed to the stock 1" bore. At the same time, I added some Hawk LTS pads to the front and a new set of rotors. Bled the system (started with 2 quarts of fluid and used all of it leaving me with a full reservoir).

Took the jeep for a test drive, and now i have very poor braking performance with a very hard pedal. Pushing hard did not lock up my stock sized tires.

Any suggestions?

Is it possible that I just need to bleed the system more?

Is it because my front pads having bedded in yet? (They do suggest several hard stops initially and then taking it easy on them for 400 miles.

I'm really out of ideas and I question how safe this thing is to drive right now. I spent about 8hrs in my garage today and am in disbelief that I've again made things worse. It shouldn't be that hard to get decent brakes. I'm not even looking for amazing. I'd settle for decent.

Thanks in advance for any suggestions.

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Unread 09-15-2013, 05:35 PM   #2
lazyxj
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Quote:
Originally Posted by mightymulhern View Post
Recently I noticed the rubber lines in back had started cracking so I replaced the hard lines along the axle and the rubber lines to the rear calipers. While doing that, I also swapped in a master cylinder from a Dodge Ram 2500 which has a 1.25" bore as opposed to the stock 1" bore.
Took the jeep for a test drive, and now i have very poor braking performance with a very hard pedal. Pushing hard did not lock up my stock sized tires.
Any suggestions?
First, go back to a stock MC.
The 1.25" Ram MC is way too big and the vacuum booster cannot provide enough boost for this large a cylinder. Anything larger than the stock 1" diameter MC doesn't have the needed boost.
While adding ZJ rear discs and then Vanco fronts, I have experimented with several MCs. I ended up using the stock MC as it provide the needed boost with just enough fluid capacity to make it all work.
Even the 1.125" Dakota MC produced too hard a pedal. With the stock MC, the pedal is lower than stock but still has enough travel to lock up the front 33"s.
To use a larger diameter MC, higher boost pressures are needed. The XJ engine bay has no extra room for a larger diameter vacuum can but a hydroboost will fit and would allow using a larger diameter MC.
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Unread 09-15-2013, 09:17 PM   #3
Azzy
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Before you put in the larger MC, did you mod the proportioning valve at all? Ive noticed my XJ with the rear disc relies too much on the fronts, not enough on the rear. Im going to do the mods as suggested here soon.

Also, I put in a full set of braided flex lines... braking feel improved a lot after that. could of just been because of fresh lines, but I know that there is now less expansion in my lines when hard on the brakes.
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Unread 09-15-2013, 09:31 PM   #4
mightymulhern
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Thanks guys.

I was afraid someone would say that the new MC was too big. Might have been nice if those claiming that it fit had shared that outcome. No one running one on an XJ is going to be stopping fast with the stock booster. Oh well. Looks like I'll by switching back. Hopefully the switch back will be quicker.

I did not mod the proportioning valve. I debated that one as well with some people posting that they removed some kind of o-ring and others warning not to. My understanding was that if you pull the o-ring you get equal bias front/rear where you really need more pressure going to the front.

I just replaced the rear lines with some universal SS ones. Perhaps I'll do the fronts too and see if that makes any difference with the old MC. Looking at the front today, the lines are old and the bleed valves on the calipers were nearly seized. Not sure how old they are, but they are definitely not new.
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Unread 09-16-2013, 01:08 AM   #5
evo_ski
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Ditch the backyard engineered brake setup. Go to a stock MC as recommended. Put in all of the compenents from the the newer gen car. Use the new disc rears but put in the ZJ prop valve and keep the factory MC.
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Unread 09-16-2013, 05:37 AM   #6
cruiser54
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The dirty little trick on the prop valve is to just swap in the guts from the donor vehicle's prop valve. Carefully remove 3/4" plug being careful cuz it's a bit spring loaded. The rest is easy. . Works great.
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Unread 09-17-2013, 10:23 PM   #7
mightymulhern
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Thanks guys!
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Unread 11-30-2013, 10:08 AM   #8
mightymulhern
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I just wanted to circle back and close this out in case someone stumbles up on the thread later asking the same question (which someone will eventually do).

In the end, I swapped the guts from a ZJ proportioning valve. I don't have the link handy, but if you do some googling, you'll find a post where someone shows the guts of the two valves. The gist is that you can pull out the end-cap/valve, spring, aluminum plunger, and rubber seal at the end of the plunger and transfer all of those parts directly from the ZJ to the XJ valve. If found mine on eBay.

I also went with a Master Cylinder from a 1998 DODGE Durango. (Centric 130.67024) It's got a 1-1/16" bore, which doesn't sound like much but actually represents at 12.9% increase. It fits under the hood, it does not require modification of the push rod from the brake booster, and the hard brake lines are a direct swap without any tweaking. This provides a noticeably firmer pedal with a full feeling range of motion but isn't so hard that you have to apply 200lbs of pressure to the pedal to stop the Jeep. I would call this the right part for the job. One note... in 1999, the Durango MC changed so you want the 1998 one which is a little more expensive.

I also used some universal Russel Performance stainless steel brake lines on all 4 corners. 2 x 657300 (rear) 2 x 657350 (front) The rear ones fit well. The front ones were just long enough. I might consider going longer next time but don't know if the next size up would be too long or not.

In the rear, the guys who did my rear disc swap cut off the stock steel tubing and added some junky fittings that rusted solid after a year. I ordered a new set of rear factory lines and bent them so that I could use the stock fittings. On both ends, the stock tubing normally goes straight to the drum. With discs, the tubing needs to be shorter. To accomplish that, I simply bent the tubing so that it turned up under the axle ending at the front side of the axle. From there, my flexible stainless steel brake lines take over. The fit is good an and there were no problems with getting the air out. This ended up being much easier than anticipated.

At present, my jeep slows down like it should. If I really get on the brakes, I can lock up the rear (not so desirable). I honestly haven't tried to lock up the fronts but the Jeep stops noticeably faster than it used to so I'm satisfied.

Last edited by mightymulhern; 11-30-2013 at 12:31 PM..
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Unread 11-30-2013, 04:40 PM   #9
KF4SQB
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I'm not sure why everyone wants to swap the guts from a ZJ proportioning valve to the XJ one. Just swap the whole ZJ valve into the XJ. The valve body is the same. The only difference is the fitting in the back of the valve. The ZJ valve has a plug in the back, while the XJ has a port for a line in the back. The port and plug are directly interchangeable. I have rear discs, proportioning valve, MC, and booster out of a ZJ in my '94 XJ, and it works great.
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Unread 11-30-2013, 05:03 PM   #10
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Originally Posted by KF4SQB View Post
I'm not sure why everyone wants to swap the guts from a ZJ proportioning valve to the XJ one. Just swap the whole ZJ valve into the XJ. The valve body is the same. The only difference is the fitting in the back of the valve. The ZJ valve has a plug in the back, while the XJ has a port for a line in the back. The port and plug are directly interchangeable. I have rear discs, proportioning valve, MC, and booster out of a ZJ in my '94 XJ, and it works great.
Because it's easier than swapping the whole valve? Some folks have rusty crap under their hoods. I live in Arizona but I still chose the easy way out. One bolt and swap the guts versus swapping the whole valve.
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If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

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Unread 12-01-2013, 05:50 PM   #11
foggybottombob
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For what it's worth, I swapped a 95 ZJ brake booster and master cylinder into my 91 XJ years ago. I don't remember all the details but that made a tremendous difference in stopping power for the 32" tires I was running at the time.
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Unread 12-01-2013, 09:40 PM   #12
XJcruiser
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I have a stock MC and prop valve and my brakes seem to be more rear bias after a disc swap.
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Unread 12-02-2013, 04:40 AM   #13
cruiser54
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I have a stock MC and prop valve and my brakes seem to be more rear bias after a disc swap.
Do they lock prematurely?

They're new disc brakes versus old drums, you know. LOL.

Mine were great right from the get-go. Swapping the guts of the prop valve after driving it for a week offered a bit more improvement.
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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