ZJ rear disk brake install on D35 with ABS:

Copyright 2004 jeep@blackonyx.net

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I finally got tired of less than par stopping coming from my XJ. This had part to do with the fact that we just purchased a 1995 ZJ that stops a great deal better than my XJ did. Upon closed inspection of the ZJ's rear brake/ axle it appeared that it would be a nearly bolt on affair to put ZJ disk brakes on my XJ's D35 axle. I also noted that the ABS tone rings on the ZJ were a different size from the XJ's ABS tone rings. However, they did have the same number of teeth. In order to keep my existing ABS system I would also need the ZJ ABS sensors and tone rings. I put a post on JeepsUnlimited.com's ZJ wanted forum. In a matter of weeks I had been contacted. For $260 I purchased the following items: ABS sensors, axle half shafts (with tone rings), calipers, disk shield, caliper mount, and rotors. Since I got the whole shafts, I can now use my old XJ shafts for trail spares. The pads needed to be replaced. The only other items I needed were the soft lines and those were purchased from the dealer, as Autozone could only get one side and I wanted to put identical parts on. The only modifications that must be done are getting the parking brake to work, making a mount for the soft lines, notching the axle flange for the ABS sensor, and wiring the ZJ ABS sensors in to the XJ's wiring.

Here are a few images of what the parts looked like before I cleaned them up:


Those images were taken just incase I forgot how everything went back together once I got it apart for cleaning. The main parts (rotor shield, caliper bracket) weren't that rust and just needed a good cleaning. The smaller items were truly rusty, but those came clean using my bench grinder and a wire wheel. I also needed to replace one of the parking brake boots as it was split. For the bracket and the shield I used Rustoleum flat black, and for the calipers and rotor hats I used VST gloss black brake paint. I had used the VST on the front brakes and it is holding up well. Below are the images once I had everything cleaned, painted, and back together:

Once I had the parts all nice and clean and ready to install, I needed to strip off the old drum brakes. The drum first had to be released (yes, my self-adjusting mechanism actually worked). This is done by holding the locking tab with one screw driver and turning the wheel several times with the other. Than it is just a matter of releasing several springs and throwing the old parts into a box, never to see the light of day again.

Shoes and other hardware removed and ready to remove axle half shafts:

Removing the axle shafts would have been pretty easy, but it turned out to be a task as I didn't have the 1/4" wrench needed to remove the bolt(the pinion mate gear shaft screw) that held the gear shaft in the diff carrier. I needed to make a trip to the hardware store at this point to purchase the correct tool. The below images show the offending bolt.

Once the bolt was removed the gear shaft easily slid out, allowing the axle shafts to be pushed in and the c-clips removed. Finally the axle shafts can be pulled out. Take care not to lose the washers behind the spider gears. Also, be careful to support the shaft to avoid damaging the bearings and seal. Once the axle shafts are out we have this view:

I didn't remove the wheel cylinder yet as I didn't want to lose any brake fluid. The ABS sensor is still present because I wasn't sure at the point if I should try to remove the whole sensor and harness or just splice in the ZJ sensor. I eventually decided to snip off the XJ sensor and solder in the ZJ sensor in.

Now the 4 bolts holding the backing plate on can be removed. One backing plate came off with ease. However,the other side needed a little coaxing with a BFH. Once that is done this is what you see:

Again, I left the wheel cylinder on to prevent fluid lose. If you have an older Jeep, than his would be a good time to replace the axle seal and bearings. Mine is a 2000, so I opted not to.

Test fitting the ZJ brake assembly to see how much axle flange must be cut away:

If you notice in the previous image, the axle studs are just the right length to fit the ZJ brake assembly. Also, you can see approximately how much material must be removed to fit the ZJ ABS sensor. The next image shows how much of the axle flange had to be removed. The cut was made with a die grinder, one cut off wheel, a Dremel and a few grinding bits. I used red paint to mark through the hole in the ZJ brake assembly, which you can still see some of. Be sure to use eye protection when doing this.

The 4 bolts to hold the XJ bracket to the axle were torque down to ?? foot pounds. Here is the assembly in place: and bolted on:

Next was the task of getting the parking brake cable to work with the ZJ parking brake assembly. This required a few modifications to the XJ cables. The part of the cable housing that attaches to the caliper bracket had to have the tabs shortened. This was done with a small cut off wheel on the Dremel. Once the tabs were shortened to an appropriate length they were than spread with a screwdriver. I didn't push it in to the bracket yet because I still had to modify the cable more. Several rings had to be cut off the spring at the end to accommodate the shortened cable length. All this is made easier if the cables are unhooked from the bracket under the back seat. I would say I shortened the relaxed spring by 1.5". I cut the rings free of the spring with the Dremel than clipped them off the cable with a pair of wire cutters. Once that is accomplished the cable needs to be bent around the brake lever and secure it with a cable clamp. Its wasn't as easy to bend the cable as I thought it would be... it was easier to bend if you moved off the bracket. Once the cable is secured, push the cable housing retainer in and make sure the clips hold. Once finished with the parking brake I cut the XJ ABS sensor off and soldered in the ZJ ABS sensor. I used liquid electrical tape followed by a layer of heat shrink tubing to ensured the integrity of the splicing and soldering.

After the parking brake I did the hard line and hose routing. I made some brackets to mount the soft line to the axle with hose clamps (will be welded later or a new mount will be made). I routed the soft line with the U section up and the hard line was bent so it came in from below the axle. The factory end on the hard line mated perfectly to the ZJ soft line, so no modifications to the hard line had to be made other than a few bends. The next image is a view from above:

A view from the bottom:


Once that is done mount the soft line to the caliper, and torque the bolt to 23 foot pounds. Than put the rotor on, install the brake pads and put the caliper on. The caliper pins were torque to 11 foot pounds. The finished product:

After bleeding and testing driving I discovered three things I still need to do. First, I had Performance Friction brake pads on the rear brakes and I soon figured out that they took way too long to get hot to become effective on the rear. I replaced those pads with some OEM quality pads. Second, I needed to adjust the parking brake. This is done by applying the hand lever, removing a plug and turing the star wheel until the wheels lock up.

The last item that I needed to take care of was the o-ring in the proportioning/combo valve. I felt as if I wasn't getting enough fluid to the rear brakes. The o-ring removal is simple. disassemble the combo valve, remove last o-ring and reassemble than bleed brakes again. Some images of that:

Once everything has been completed I now have more than adequate braking power.


Clean up took about an hour:


Since I have been driving with the brakes for a while I feel that there is too much fluid going to the rear brakes. With my ABS disabled I can easily lock the rear brakes up under heavy braking. This will be fixed by replacing the XJ proportioning/combo valve with one from a ZJ.