So I've been trying to look into doing a junkyard (ZJ) rear disc replacement on my 99 with a 29 spline 8.25 but I'm having proublems finding info or threads on anything other than 35 disc swaps. I do realize I'd proubably have to upgrade the master and maby the booster but I dont really know were to start . Any info, or known threads I can look up would help.

 

I'm going to being doing the swap hopefully this coming weekend. Here are is a write up and info on how to do it...

http://home.swbell.net/rriojas3/reardisk.html
http://go.jeep-xj.info/HowtoZJvalve.htm

You can either use the ZJ brake cables or order some from Napa...MJS302 has the part numbers for it (thats what I did).
https://www.cherokeeforum.com/f2/zj-...e-cable-36835/

As far as I've read, the master cylinder is the same between Grand and Cherokees. Only thing needs to be changed is the propositioning valve.

 

You already have a dual diaphgram booster so you won't need to "upgrade" that. You will need to get the ZJ prop valve though, otherwise the disk swap will be useless. Disk brakes take more fluid than drums, therefore you need the ZJ prop valve.

Other than that you'll need the backing plates, dust shields if you want an ebrake, the soft brake lines, calipers, rotors. The tubes on the d35 are obviously smaller than the 8.25 so you'll need to take a dremel or tool of your choice and make the hole on the backing plate bigger so it fits over your 8.25.

Pretty straightforward swap really.

 

where is that prop valve located off the ZJ?

 

Right off of the master cylinder.

 

i have a 1999 xj with 8.25 chrysler 29 spline and i swap to grand cherokee dana 35 disk brakes few weeks ago. it works great with a factory xj prop valve and emergency cables. my xj runs with 33x12.5x15 tires on it

 

Thanks, I think I'm going to go ahead and pick up the parts next time I'm at the JY