If you’re tired of the rear drum brakes on your XJ it’s easy to swap to rear disks using ZJ (93-98 Grand Cherokee) brakes. Just like some XJs, ZJs have a Dana 35 rear axle and some of the ZJs were built with rear disk brakes which is why the parts will bolt up.

Parts List

Note: This guide is written for XJs with a Dana 35 rear axle but should also work for those with a Chrysler 8.25 rear axle. You’ll likely need to grind out the center hole of the backing plates to fit the larger axle tubes of the Chrysler 8.25. If your not sure which rear axle your XJ has, check out this guide.

You’ll need to source all of the following parts. The cheapest route will be to scavenge them off a ZJ in a junkyard, but if none of the junkyards near you have any ZJs you can buy new parts online.

Part	Part Number	Quantity
ZJ driver rear caliper	Power Stop L4398	1
ZJ passenger rear caliper	Power Stop L4399	1
ZJ rear rotors	Centric 12067032	2
ZJ rear pads	Power Stop 17666	1
ZJ backing plates	Crown 476212829K	1
Custom driver parking brake cable	RT Offroad RT31041	1
Custom passenger parking brake cable	RT Offroad RT31040	1
ZJ Prop valve from a ZJ with rear disk brakes	Mopar 52009129, or Mopar 52009061	1
ZJ Rear wheel studs	Dorman 610-234	10
ZJ rear disk rubber brake lines	Sunsong 2203837, Sunsong 2201229	1 of each
Rear diff fluid	80w90 diff oil (for non LSD rears)	1.75qts
3/16 brake line	n/a	~10ft
3/8-24 brake flare fitting	n/a	4
Brake fluid	DOT 3 / DOT 4	1qt
Big zip ties	n/a	2 - 3

Remarks:

Any ZJ specific parts will work. I listed part #s for Power stop / Centric / Crown above for those that want an easy to follow list.
There’s no difference in rear brakes between the i6 / v8 ZJ models.
When searching for ZJ parts, don’t use 1993 as the model year. ZJs only came with drum brakes in 93.
Others have used ZJ / KJ parking brake cables with good results but I opted to go with the custom cables for simplicity.

Warning: Replacing The Rear Wheel Studs Is Mandatory

The factory wheel studs on your XJ are too short to use with disk brakes because rotors have a thicker center hub (0.25" thick) than drums (0.15" thick) so less of the studs will be sticking out. Given studs are so cheap and you’ll already have the axle shafts pulled there really isn’t any good reasons to skip this step. At best you save a couple bucks, at worst you lose a wheel while driving.

Dorman 610-234 studs are perfect because they’re 1.465" long which is roughly 0.09" longer than the factory studs.

If you’re interested in running wheel spacers you could step up to the Dorman 610-449 studs which are 2.078" long.

Part	Part #	Length
OEM XJ drum wheel studs	Mopar 83503053	1.375"
ZJ rear disk wheel studs	Dorman 610-234	1.465"
Extended ZJ rear disk wheel studs	Dorman 610-449	2.078"

Steps

Start off by putting the rear of your XJ up on jack stands and remove the rear wheels. I’d recommend doing this on a flat surface because you’ll need to shift into neutral to rotate the diff later on.

Disassembly

Remove the rear drums. This may require a sledge hammer if you live in a rust prone area. (mine did)

Go underneath the Jeep and drain the rear differential by removing the diff cover. We’ll need to remove the axle shafts because they are blocking the backing plates from being removed.

Shift the Jeep into neutral and rotate the diff until you see the center pin bolt. It’ll be a tiny bolt that may be 6pt or 12pt. Mine was a 1/4" 12pt bolt.

Remove the bolt and slide the center pin out.

Push the axle shafts towards the center of the Jeep until you can see the c clip and pull it out. Now you can pull out the axle shafts.

The axle shafts are slightly different lengths. (Driver side is longer)

Set the axle shafts aside for the moment and remove the drum hardware.

I opted to cut an access hole on the backing plates so I could remove the wheel sensors without having to unplug them from the body yet.

Remove the brake line from the backside. You’ll want to put a catch pan down for the brake fluid that’ll drip out.

Remove the 4 nuts securing the backing plate.

Now repeat all of this on the other side.

Replace the Wheel Studs

Go ahead and swap the wheel studs on both axle shafts. The easiest way to do this is via a press.

I repurposed an 02 sensor socket to press the new studs in.

Length comparison of the new studs vs old.

Done.

Reassembly

At this point you can start putting the new parts on. Begin by installing the disk backing plates and torquing the 4 nuts on each side to 45 ft-lbs.

Some aftermarket backing plates will be labeled with an “L” (driver side) or “R” (passenger side) to indicate their orientation, but if they don’t make sure the caliper mounting bracket is on the rear.

Go ahead and slide the axle shafts back in. You’ll want to push them in as far as they can go to prep for installing the c clips.

Go underneath the jeep and pop the axle C clips back in.

After you put each c clip back into place, push the shaft outwards to secure the clip.

Re-install the center pin and bolt. There’s no official torque spec for the bolt but don’t go crazy on it. It’s a tiny bolt and you’re gonna be in a world of pain if it snaps.

Once the c clips / center pin are re installed you can seal up the diff with RTV and fill it with fluid. Torque spec for the cover bolts is 20 ft-lbs.

Install the Rotors / Pads / Calipers

If you’re using aftermarket pads it’s never a bad idea to test fit them before greasing up the slides. I’ve found some aftermarket pads to be too long and need to be ground down by the slides and this is significantly easier to do before any grease is applied.

Once the pads are good you can pop them onto the caliper and then install the caliper.

Torque spec for the caliper bolts are 7 - 15 ft-lbs.

DIY Rubber Brake Line Brackets

Drum brakes don’t use rubber brake lines because they are stationary but calipers can slide in and out so they require rubber lines to compensate.

The rubber brake lines are pretty cheap and easy to install but they’ll require a bracket to attach to.

You could probably get away with using a zip tie to secure them to the axle but it’s not overly difficult to hack together a DIY bracket. I made mine out of 1/8 angle that I welded to the axle.

Hook Up the Brake Lines

At this point you can either re-use the existing brake lines or make new ones. I opted to replace mine since they were showing their age.

Old lines removed.

New lines installed.

Swap the Prop Valve Or At Least the Spring

The only difference between the XJ prop valve and the ZJ rear disk prop valve is the spring inside of it. This means you can save a lot of time by just swapping the spring instead of completely swapping the prop valve.

Spring from the ZJ prop valve

When removing the spring from your XJ prop valve be sure to hold the prop valve so you don’t strain the brake lines. A little brake fluid will leak out so a paper towel can be handy for catching it.

Comparison of the two springs.

Don’t over tighten the nut.

Disable ABS

If your XJ had ABS and you want to disable it, you can do so by removing 1 relay and 2 fuses in the under hood fuse box. On a 97-01 XJ this should look like the following.

Then you can remove the rear ABS sensors. The plugs are located underneath the rear seat on the driver side.

Unplug the red / black connectors then route the wires out through their holes.

Plug up the holes with some 0.5" grommets or maybe slap some seam sealer in them.

Go underneath the Jeep and remove the sensors.

Bleed the Brakes

The rear brakes lines need to be bled since there’s going to be air trapped in them. Start off with the passenger rear brake since it’s longer and then do the driver rear brakes.

Install The Parking Brake Cables And Adjust It

If you haven’t already, disconnect the old parking brake cables from the adjuster. This can be done by loosening the nut on the adjuster until there’s enough slack in the lines to unhook them.

Hook up the new lines. (Shorter line goes on driver side)

Use one or two large zip ties to secure the lines to the axle.

Keep the lines somewhat loose and don’t tighten up the adjuster yet because you’ll need adjust the parking brake shoes on each side.

You can do this by removing the rubber plug on the back side of the backing plate and adjusting the parking brake by turning the brass star until you can feel the parking brake starting to drag when turning the rear wheel. Both sides will need to be done.

Once that’s taken care of you can tighten the adjuster nut and test the parking brake lever to ensure it locks up the brakes.

All Done

If you made it this far, you should be all done and ready for a test drive. Be sure to pump the brakes before shifting it out of park for the first time.

(Small zip ties are temporary and will be replaced with proper ones)

FAQs

Can I keep ABS?

Yes, but it’ll require some modifications and a set of ZJ rear ABS sensors. You’ll need to cut a hole in the backing plates to fit the ABS sensor through (if using aftermarket backing plates), and make a custom bracket to hold the sensors by the axle tone rings.

Do I have to replace the parking brake cables?

Ideally yes. While the parking brake cables for drums and disks are the same lengths, they have a different end on the wheel side. Others have modified the drum parking brake cables to attach to the calipers via a cable wire clamp but I’d suggest just spending the extra for the proper cables as they aren’t that expensive.

Do I need to get new backing plate studs?

Nope. The disk backing plates are about the same thickness as the drum backing plates so there should be no issue.

Why do I have to change my prop valve?

Disk brakes require less fluid pressure to engage. This means that while the XJ prop valve will work for disk brakes, it’s also very likely going to lock up the rear brakes sooner than it should because it’ll be sending too much pressure to the back brakes.

This isn’t something you’ll notice during normal driving but it can make your XJ behave unexpectedly during heavy braking.

Can I reuse my existing brake lines?

Yes as long as your careful when making new flared ends on them. Given XJs are now at least 25 years old there’s really no harm in running new axle lines.

Where did the torque specs come from?

Torque Spec	Amount	Source
Backing plate mount nuts	45 ft-lbs	96 ZJ FSM page 3-31
Caliper mounting bolts	7-15 ft-lbs	96 ZJ FSM page 5-33
Diff cover	20 ft -lbs	https://www.jeepforum.com/threads/torque-spec-for-backing-plate-dana-35c.820200/

XJ Rear Disk Conversion