Doing the rear ZJ to XJ disc swap...

Tony_SS · Apr 18, 2014

I'm going to try and tackle this on Saturday. Any pointers to share?

I have the ZJ prop valve, should I use that?
How much area of the backing plates do I have to remove to fix over the rear housing?
Any other tricks to getting the axles removed? Just pop the cover, undo the bolt and let the pin slide out?

Those are my big concerns so far.

WB9YZU · Apr 18, 2014

Did you read the FAQ or review the thread with it?
Edit: I thought for sure there was a FAQ on this. I know there are many threads which cover it in detail.
Ah, at bottom of this thread: http://www.naxja.org/forum/showthread.php?t=1025817

#3. No. Remove the pin, push the axle in, remove clip, pull axle out.

-Ron

the_midwesterner · Apr 18, 2014

Here you go!

I personally used the jeepforum page as a guide. Its prettry straight forward and these 2 guys documented the swap very thoroughly. This should answer all of your questions.

http://www.cherokeeforum.com/f51/rear-zj-disc-brakes-cherokee-xj-chrysler-8-25-a-57807/

http://www.jeepforum.com/forum/f11/zj-rear-disc-conversion-8-25-write-up-whole-truth-607435/

Tony_SS · Apr 18, 2014

I haven't seen the jeepforum one yet... Thanks guys.

yossarian19 · Apr 20, 2014

Did this in 2007 or 2008.
As I recall...
Change the shuttle valve & spring from the ZJ valve into the XJ one.
You may / may not have to drill the backing plate mounting holes to fit the lugs on your axle. You "should" change the backing plate studs out for longer ones, as the ZJ disc plate is thicker than XJ drum stuff and the nuts won't fully engage. I didn't and I haven't had any issues since 2007 (or 8?). The center bore, you'll need to open up some. Go slow, tighter is better up to a point.

Pop the cover, pull the pin, push axles inward & remove C clip. Yep. that's all.

You'll need to modify the hard lines to work with the ZJ soft lines (shorten them is all), and mount the ZJ soft lines to something. I welded a 1/4-20 bolt to the axle housing.

Make sure you mount the calipers with the bleeder screw at the top of the caliper / pointing up.

Use quality brake friction, but note that I used garbage & it's still a lot better than drums back there.

amorth · Apr 20, 2014

Hey Tony, I'm tackling this same project on Monday with a ZJ kit I bought off a guy over on CF. Any advice you can pass along? Did you run into any weird problems? I hope it all went well for you.

markw · Apr 20, 2014

The valve is the same, just pop the end cap off the prop valve and swap springs with the ZJ one.

Tony_SS · Apr 20, 2014

Thanks all. I'm actually doing it next weekend, I will take pics and do a write up here.

I have the ZJ prop valve.

Can I just get a set of new wheels studs from the front and use them in the rear, since they are longer?

OverlandZJ · Apr 20, 2014

The valves inside the prop are different.. use all the internals including the end cap from ZJ donor.

Tony, what axle are you retrofitting? On my XJ44 i had to clearance the rotor ID also.

MagicNelson · Apr 20, 2014

On removing the axle shafts: yep, just pop off the cover and undo the bolt that holds the crosspin into place. The spider gears will fall out. Then you can remove the c clips (they usually just fall off) and the axles will pull right out.
On the backing plate, I used one from a KJ so I didn't have to modify it at all but make sure to get longer bolts (someone else mentioned that earlier) since the backing plate is thicker. Also, make sure to use locktite on those bolts.
If your jeep has any rust on it, be careful with the brake fittings that will connect to your new rubber hoses that go to the calipers. I had to cut and flare both of my hard lines which added a lot of time to the job. That's about everything i can think of. Good luck!

yossarian19 · Apr 20, 2014

Oh yeah.. wheel studs... the stock ones are fine for steel wheels. Kind of marginal for alloys. I've run stock studs and alloys for a while. I don't like it but neither have I had a single cause for complaint.

WB9YZU · Apr 21, 2014

One of the articles I read recommended ZJ studs.

I would get stock front '97 though '01 studs instead.

-Ron

Edit: I knew this was around somewhere...
http://naxja.org/forum/showthread.php?t=1102429&highlight=Brake

amorth · Apr 21, 2014

For those that have done this before, what did you do with the brake line after it was disconnected from the drum? Did you immediately connected it to the new caliper so you wouldn't lose bake fluid? I've read just about every write up out there on how to do this upgrade, I'm just confused on what to do right after I remove the brake line from the drum.

MagicNelson · Apr 21, 2014

Don't worry about it. You won't lose much fluid at all. Putting a slight bend in the hard line so it's tilted up to prevent dropping worked well for me.

markw · Apr 21, 2014

I'm pretty sure the valve was the same. Spring is definitely different. You'll have them both open at the same time so just compare them. Swapping the guts is less work than moving all the lines over, and takes like 5 minutes. I did mine 6-7 years ago. Stops great.

OverlandZJ · Apr 21, 2014

markw said:
I'm pretty sure the valve was the same. Spring is definitely different. You'll have them both open at the same time so just compare them. Swapping the guts is less work than moving all the lines over, and takes like 5 minutes. I did mine 6-7 years ago. Stops great.

Had to dig a bit but i found pics i posted here some time ago, show's the "valve" or plunger as i called it years ago having a larger OD on valve and end cap.

http://naxja.org/forum/showthread.php?t=978214&highlight=prop+valve+plunger

whitexj98 · Apr 21, 2014

I swapped valve and spring.

Bjorn86 · Apr 21, 2014

OverlandZJ said:
Had to dig a bit but i found pics i posted here some time ago, show's the "valve" or plunger as i called it years ago having a larger OD on valve and end cap.

http://naxja.org/forum/showthread.php?t=978214&highlight=prop+valve+plunger

x2. I found the same thing when I did mine. I used the ZJ cap, plunger, o-ring, and spring in the XJ prop valve housing. Seems to be working great.

Tony_SS · Apr 21, 2014

Basic question... when swapping out the prop valve only, do I have to bleed the system?

Tony_SS · Apr 21, 2014

OverlandZJ said:
The valves inside the prop are different.. use all the internals including the end cap from ZJ donor.

Tony, what axle are you retrofitting? On my XJ44 i had to clearance the rotor ID also.

C8.25 rear axle

Doing the rear ZJ to XJ disc swap...

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