Rear Disc Swap mods

ok i wanna do a rear disc swap on my 8.25 or put in a 8.8 soon and was wondering what you guys do to compensate for the rear disc brakes in term of brake fluid proportioning. i have rear that many people just take the little piston tyoe thing out of a ZJ prop valve and drop it into their XJ prop valve. has anyone had good experiance with this? i had an 8.8 in my old 90 XJ but i also removed the ABS and installed reg brakes into uit and it was a disaster, the brake on my old XJ sucked nuts. i wanna build my new 97 XJ propper and not cut any corners so i can be proud lol

Here is what I did, It worked great.
http://www.jeep-xj.info/HowtoPvalve.htm

Search Zj prop valve swap here & you will find a ton of good info.

I searched Disc breaks and found this and many others.

http://www.naxja.org/forum/showthread.php?t=989827&highlight=disc+break+conversion

I just did/am doing this. It's pretty straightforward. You do want to replace the wheelstuds, as they are just too short (imo); I bought some new studs at NAPA.
The studs that hold the backplates on may be long enough that you don't need to replace them; mine ended up flush with the nuts (you ideally have 1-2 exposed threads), so I just red-locktited them. For the softlines, I welded a 6mm(?) bolt to the axle tube so I could just bolt down the line. It's very rigid this way.

If you do decide to do this, I have an complete extra set of rear brakes (backing plates, calipers, rotors, pads, lines, etc.) I was going to use to swap my cousin's XJ before he bailed on me. Let me know if you are interested.

I just did this with a D44. Over years of pick and pull salvaging I had grabbed various proportioning valves and compared them. The link below shows the difference in spring length. There are other links out there and the one already included is pretty good, but others show that actually the way the plungers seat may be a little different. To sum up my research:

1: You need the guts out of a rear disk ZJ the ones with drums seem to have a valve that is more like the XJ. (not surprising)
2: I looks to me like the housings are all the same.
3: This is all about limiting hydraulic flow to the rear disks in extreme braking situations.
4: Just pulling the seal does not make much sense to me. I can see that it would work but why not just go get the right part?

To conclude
I had a whole valve of a rear disk ZJ and I had the brake booster and MC out so I just swapped it. I actually think that just swapping the piston and rod would be a whole lot easier IF you have access but your mileage may vary and I can only speculate that the housings are the same. You will need to remove and rethread the end cap under spring tension so be prepared. I love the new setup and it is hard to lock up the rear brakes now but they will before the fronts. The worst part of the conversion for me was dealing with getting new calipers. I ended up with a Wagner caliper that had been mislabled and I will tell you that if you try and bleed brakes when your bleed valve is higher than your flexible hose you will not be happy. I only mention this because if you grab the later Crown Vic brakes you will have to deal with the fact that one is designed to be leading and if you make it trailing the bleed valve will be wrong. This second thread covers this.




http://www.jeepforum.com/forum/f11/rear-discs-438001/index2.html

http://www.naxja.org/forum/showthread.php?t=1074326

Good Luck I appreciate that you are trying to do it right.

nick

nickguy said:

I just did this with a D44. Over years of pick and pull salvaging I had grabbed various proportioning valves and compared them. The link below shows the difference in spring length. There are other links out there and the one already included is pretty good, but others show that actually the way the plungers seat may be a little different. To sum up my research:

1: You need the guts out of a rear disk ZJ the ones with drums seem to have a valve that is more like the XJ. (not surprising)
2: I looks to me like the housings are all the same.
3: This is all about limiting hydraulic flow to the rear disks in extreme braking situations.
4: Just pulling the seal does not make much sense to me. I can see that it would work but why not just go get the right part?

To conclude
I had a whole valve of a rear disk ZJ and I had the brake booster and MC out so I just swapped it. I actually think that just swapping the piston and rod would be a whole lot easier IF you have access but your mileage may vary and I can only speculate that the housings are the same. You will need to remove and rethread the end cap under spring tension so be prepared. I love the new setup and it is hard to lock up the rear brakes now but they will before the fronts. The worst part of the conversion for me was dealing with getting new calipers. I ended up with a Wagner caliper that had been mislabled and I will tell you that if you try and bleed brakes when your bleed valve is higher than your flexible hose you will not be happy. I only mention this because if you grab the later Crown Vic brakes you will have to deal with the fact that one is designed to be leading and if you make it trailing the bleed valve will be wrong. This second thread covers this.




http://www.jeepforum.com/forum/f11/rear-discs-438001/index2.html

http://www.naxja.org/forum/showthread.php?t=1074326

Good Luck I appreciate that you are trying to do it right.

nick

Click to expand...

thanks,thats some good info that i'm gonna use from thisto go into mine.

If u want to do the zj rear disc brake swap. I have most of the parts sitting in the garage after getting rid of my d35 for a d44. I will sell them to u for $75 obo let me know. I don't have the inner drum/e brake parts. Springs and shoes. I believe that your 97 has a duel diaphragm brake booster like my 94 does. I did not need to change out the valve. The brakes worked fine and if u jam on the brakes really had u can lock them up with 35" tires.