If you've spent any time looking under your old Grand Cherokee lately, there's a good chance your jeep zj rear brake backing plate looks more like a piece of Swiss cheese than a solid metal component. It's a common sight for anyone living in the rust belt or anyone who actually takes their ZJ out on the trails. These things are notorious for rotting away, and while it might seem like a minor cosmetic issue, it's actually a pretty big deal for your braking system, specifically that finicky parking brake we all know and love.
The ZJ, produced from 1993 to 1998, is a legend in the Jeep world, but it's definitely reaching that age where "routine maintenance" starts to involve a torch and a lot of PB Blaster. The rear backing plate is one of those parts that most people ignore until they try to set the parking brake on a hill and realize it doesn't hold at all—or worse, they hear a horrific grinding sound coming from the rear end because the plate has literally collapsed inward.
Why these things always seem to rot out
Most Jeep ZJs, especially the later models, came with rear disc brakes. It was a big selling point back in the day. However, Jeep used a "drum-in-hat" design for the parking brake. This means there's a small set of brake shoes tucked inside the center "hat" of your rear rotor. The jeep zj rear brake backing plate serves as the mounting surface for those shoes.
Because of where it's positioned, it catches every bit of road salt, mud, and moisture kicked up by the tires. Since it's made of relatively thin stamped steel, it doesn't take much for corrosion to take hold. Once the rust starts, it eats away at the thin metal around the mounting pins for the parking brake shoes. When those pins pull through the rusted metal, your parking brake shoes just kind of flop around inside the rotor. It's noisy, it's annoying, and it can actually lock up your rear wheel if you're unlucky.
Finding the right replacement part
Tracking down a new jeep zj rear brake backing plate used to be a real pain. For a while, you had to scour junkyards, which was usually a waste of time because every ZJ in the yard had the same rusty mess you were trying to replace. Thankfully, companies like Crown Automotive and some aftermarket specialists started stamping these again.
When you're shopping, make sure you're getting the ones for the disc brake rear end (which is what 95% of ZJs you'll be working on have). There are left and right specific plates, so don't accidentally buy two of the same side. Also, keep in mind that the backing plate is often sold as a "dust shield" or "backing plate assembly." If you can find the assembly that includes the parking brake lever and hardware, grab it. It'll save you the headache of trying to transfer your old, crusty hardware over to the new shiny plate.
The "While You're In There" reality
Here is the thing about replacing a jeep zj rear brake backing plate: it is not a five-minute job. You can't just bolt it on from the back. Because of the way the Dana 35 or Dana 44a rear axle is designed, the axle shaft has to come out to get the backing plate off.
Since you have to pull the differential cover and C-clips to slide those shafts out, you really should plan on doing a few other things at the same time. You're already going to be covered in gear oil, so you might as well replace the rear axle seals and maybe even the wheel bearings if they've been humming. You'll definitely need fresh gear oil and a new gasket (or a tube of RTV) for the diff cover. It turns a "brake job" into a "Saturday afternoon project," but doing it right the first time means you won't have to touch it again for another decade.
Tearing it all down
First off, get that Jeep up on jack stands. Don't be that person trying to pull axle shafts on a floor jack; it's just not safe. Once the wheels are off, you'll need to remove the brake calipers and the rotors. If your backing plates are really bad, the rotors might be stuck on the parking brake shoes. A few light taps with a dead-blow hammer usually does the trick.
After the brakes are out of the way, it's time to dive into the differential. Pop the cover, drain the fluid, and find the cross-pin bolt. Be careful with this bolt—if you snap it, your day just got a whole lot worse. Once the pin is out, push the axle shafts inward, pop the C-clips, and slide the shafts out. Now, finally, you can get to the four bolts holding that jeep zj rear brake backing plate to the axle housing.
Installing the new backing plate
Once the old plate is off, take a wire brush to the end of the axle housing. Get all that old scale and rust off so the new plate sits flush. I like to throw a little bit of paint or even a thin layer of anti-seize on the mounting surface to slow down future corrosion.
Bolt the new jeep zj rear brake backing plate on and torque those four bolts down. If you bought a bare plate, you'll need to move your parking brake actuator lever over. This is usually the part where people start swearing, as those little springs can be a bit stubborn. Having a dedicated brake spring tool makes this a lot easier, but a good pair of needle-nose pliers and some patience will get it done.
When you slide the axle shafts back in, be super careful not to nick the new seals (assuming you replaced them). If you're reusing the old seals, make sure they aren't leaking before you put everything back together. Pop the C-clips back on, reinstall the cross-pin, and button up the differential.
Finishing up and adjustment
After you've got the rotors and calipers back on, don't forget the most important part: adjusting the parking brake. There's a little star wheel accessible through a slot in the back of the jeep zj rear brake backing plate. You want to adjust it until the shoes are just barely touching the inside of the rotor hat. You'll know you've got it right when the parking brake handle inside the Jeep clicks about 5 to 7 times and holds the vehicle firmly.
If you skip the adjustment, you've basically just installed a very expensive dust shield. The whole point of that plate is to provide a solid foundation for the parking brake, so make sure it actually works!
A quick word on the Dana 44a
If you happen to have a ZJ with the V8, you might have the Dana 44a (aluminum) rear end. The process is mostly the same, but the parts are slightly different. The backing plates for a Dana 35 and a Dana 44a aren't always interchangeable depending on the year, so double-check your axle type before hitting the "order" button. The 44a is a beefier axle, but that aluminum center section means you have to be a bit more careful with torque specs on the diff cover bolts.
Wrapping it up
It's definitely a chore, but replacing a rotted jeep zj rear brake backing plate is one of those jobs that makes your Jeep feel "tight" again. No more random rattles from the back end, no more worrying about the Jeep rolling away when you park on an incline, and no more crunchy sounds every time you hit a bump.
It's one of those classic ZJ maintenance tasks that separates the casual owners from the people who really want to keep these rigs on the road. Grab some brake cleaner, a drain pan, and maybe a buddy to help you wrangle the axle shafts, and just get it done. Your ZJ will thank you for it, and you'll feel a lot better next time you have to use that emergency brake.