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ZJ rear disc brake conversion

R

Rocket689

NAXJA Forum User
Location
Oley, PA
I am doing a ZJ disc swap on a chrysler 8.25 29 spline. From what I have read, the hole in the ZJ backing plate needs to be bored out bigger to fit the 8.25. Does anyone have the measurement of the diamenter of where the backing plate sits on the axle? I don't want to tear apart my DD to measure if I don't need to in order to get the boring done. :wave1:
 
It only needs bored out like a hair. Not even worth taking measurments for.


Take your old brakes off...grind out the new backing plates until they fit. Shouldnt take more than 30 minutes to get both sides on!
 
I dont think anything has to be done on a 8.25",you do for like a D44.
 
Take a caliper and measure the outside diameter of the axle tube. That'd get you a dialed in measure measurement to work from. :sunshine:

I did the teraflex rear disk brake upgrade on mine and love it. Mongo stopping power for rock crawling party1:
 
an 1/8" would definitely be enough to get it to fit. I had to do it to my 27-spline 8.25. XJChris(you gonna check out the vintage grand prix?--I'll be there) is right--it shouldn't take but 30 min to get them both on.
 
Thanks for everyone's input. :yelclap: When I bought the ZJ disc parts, I also got the ZJ proportioning valve. Do I need this? I know some people do not use it, but is there any benefits?
 
I just might have to break down and hit the PnP, my rear brakes are starting to get a little grabby. I'd hate to throw any money at the stock drums.
 
Rocket689 said:
Thanks for everyone's input. :yelclap: When I bought the ZJ disc parts, I also got the ZJ proportioning valve. Do I need this? I know some people do not use it, but is there any benefits?
Click to expand...
well you should (depending on year) upgrade the MC to a dual diaphram. And using the ZJ PV would get you the proper placement of fluid to the front and back for disk brakes and not the amount for drums/disks. have heard of people using the factory PV with their rigs but not really sure how much of your rear disks are being not used.
 
According to Go Jeep's site, you can swap the piston and spring from the ZJ's PV into the XJ's PV and bypass messing with the PV mount and brake lines.
It what I did.
http://go.jeep-xj.info/HowtoPvalve.htm

Adding the ZJ discs was one of the better modifications done to my Cherokee.
I do have a lower brake pedal now, so the bigger WJ mater cylinder is next on the list.
 
Rocket689 said:
I am doing a ZJ disc swap on a chrysler 8.25 29 spline. From what I have read, the hole in the ZJ backing plate needs to be bored out bigger to fit the 8.25. Does anyone have the measurement of the diamenter of where the backing plate sits on the axle? I don't want to tear apart my DD to measure if I don't need to in order to get the boring done. :wave1:
Click to expand...


Why not just get a 8.8
 
i just did this conversion a couple of weeks ago. have a 97 with the 8.25. it only took me about ten minutes on each side to enlarge the hole on the backing plate. i used a dremal and just kept checking it until it fit. as for the prop. valve i also got the ZJ one and have not installed it. i think it works good without it. i will wait until a day when Im really bored to put it on and see if i can feel the difference.
 
emr1101 said:
Why not just get a 8.8
Click to expand...

some people dont have the cash to do an axle swap. others may not know how to weld so they would need someone or a shop to weld on the new spring perches and shock mounts.

I did the ZJ D44A disk swap on my 95 xj with an 01 xj 8.25 on it. I only had to take a little off of the bracket, not even enough to wear out a dremel grinding drum. its not enough to need to take to a machine shop, even if you work there. i would venture to say it is most likely less than 1/32 of an inch all the way arround. the bolt holes also need to be dremeled out a little more than the center hole, but again not bad.

at the same time i swapped in the zjs proportioning valve innards. two pieces and the cap. pretty easy. i also drained MOST (read not dry) of the fluid out of the mc to replace the brake fluid with new fresh stuff.

by far a super easy mod. im kicking myself for not doing it sooner and for being nervous about doing it beforehand.
 
I too swapped the zj prop spring in(it's 1/2" shorter in case some of you want to mod your existing spring or just to know the difference). Having a 96, I already had the dual diaphragm booster.
 
Hey, I did the swap on my '97, 1/8 inch is more than plenty, you will need to make the 4 holes for the studs slightly larger too. I went with the ZJ PV just because. I stuck with the 8.25 over the 8.8 because the 8.8 is narrower and would required spacers. Haven't tried locking it up just because I have the WJ calipers in the from and the ZJ calipers in the rear, but it will stop in a hurry. :) That was the point! Well just to give you a comparison my friend has 33's on his XJ with stock brakes, I can stop faster than he can even with the ski boat in tow. You may want to replace the outer bearings and seals when you do the swap, keeps you from possibly tearing it down twice.

JT
 
Thanks for everyone's input. I am just gonna swap in a ZJ PV since I already have it. I did the swap on Saturday. Everything went great except for the fact that the ZJ setup I had bought had 2 driver side backing plates. Anyone know where I can get one passenger side ZJ Rear disc backing plate?? :gonnablow
 
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