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  #1  
Old September 12th, 2009, 21:11
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DougJ DougJ is offline
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Another Disc brake install

My '01 is slowly evolving, and one of the things I've been planning is disc brakes for the rear. Since I got back from Iraq in May I've installed a RigidCo front bumper, HP D-30 with 4.56 gears and ZJ steering, and 4.56's in the the Chrysler 8.25 to match. I've been watching the yards in the meantime, looking for a ZJ with disc brakes. I found a '95 last weekend and took the backing plates / mounts, calipers, soft lines, and hardware. I didn't have a 12 point 1/4 inch to pull the pin from the carrier so I had to run and get that to finish. Dummy.

It ended up costing me about $58 for the parts The hardware I took included the caliper mount bolts, backing plate mount studs and nuts, and 8 good wheel studs.



From left to right here's the stock XJ wheel stud, disc brake ZJ wheel stud, new replacement ZJ stud, XJ backing plate stud, and ZJ backing plate stud. The nut is just there to keep the new stud from rolling away.



Stock brake assembly:



Axles and brake parts removed:





ZJ backing plate with new parking brake pads. The center bore of the backing plates had to be opened up by approximately .040" to fit over the 8.25 housing. I also had to slightly elongate the mount holes to get a smooth fit. Those junkyard parts cleaned up nice.



Completed assemblies, the brake lines are not hooked up yet though. I ended up flipping the ZJ soft lines from going up from the caliper to down, and I rotated them 180 deg on the mounting surface. This has the soft line mount plate sitting just under the spring pad. I'm going to weld a small tab on there to solidly mount the lines. I just made a loop in the stock lines to take up the extra length. I don't have picture of that yet.





I bought rotors, ceramic pads, parking brake shoes, 4 ZJ wheel studs, and fluids for front and back, including friction modifier for the trac-lok, at Napa for about $180. Since I just had the rear re-geared and the front gears are also fresh it's time for a fluid change, but no need for new bearings and seals in the rear axle. So I'm in for about $240 for my disc brakes so far. I'm thinking of installing Liberty e-brake cables rather than modifying my cables. They're about $40 each at Napa. So no parking brake at this point. I'm going to be installing fresh rotors and pads up front soon. I've been considering the WJ brake mod up front, but we'll see how things work out for a while.

So how do they work? They've only been on there for a day or so, but they feel good! Not as strong as I wanted at first, so I'm trying the Go Jeep proportioning valve mod right now. Seems better, and once I freshen up the front I think it'll be very even front to back.

Doug
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  #2  
Old September 12th, 2009, 22:34
WB9YZU WB9YZU is offline
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Re: Another Disc brake install

Very clean and looks easy enough to do!

Keep it updated

Ron
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  #3  
Old September 13th, 2009, 11:29
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Re: Another Disc brake install

Yeah, I need to finalize the brake line mounts and hook up the ebrakes. Time (and servicing the front brakes) will tell how much overall improvement there is. Definitely worth it right now though. Not much time involved either, except for JY parts cleaning I think I have about 4 or 5 hours in it. I have to get some pics of the brake line routing, ugly but effective.

Here's something only a Jeep geek would notice!
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Old October 15th, 2009, 08:19
srmitchell srmitchell is offline
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Re: Another Disc brake install

This looks great.

I'm pulling some zj brakes this weekend from the bone yard. A few questions...
-What special tools are needed for the zj axle? I've done an aussie, but i don't want to go unprepared.
-Did you get the zj studs to work with the xj shafts? I know they need to be longer, Im running moabs also.
-How hard is it to modify the prop valve?
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  #5  
Old October 15th, 2009, 08:24
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JNickel101 JNickel101 is offline
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Re: Another Disc brake install

I didn't think you needed to mod the prop valve on the newer XJs....?
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  #6  
Old October 15th, 2009, 09:25
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dgrigorenko dgrigorenko is offline
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Re: Another Disc brake install

Quote:
Originally Posted by JNickel101 View Post
I didn't think you needed to mod the prop valve on the newer XJs....?

yes you definatly do.... well i have a 99, and it definatly needs the prop valve... i dont know about the 00 and 01
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Old October 15th, 2009, 09:30
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Re: Another Disc brake install

Quote:
Originally Posted by JNickel101 View Post
I didn't think you needed to mod the prop valve on the newer XJs....?
Newer XJs have the same proportioning valve as any old one and it "can" (some say "should" or "must" ) be modified when you go to rear discs, as they need more fluid to operate properly.

The thing that changes in the XJ braking system is the brake booster - in the 97 changeover the XJ got a dual diaphragm unit that works much better.

As for the wheel studs - it depends on your wheels. If you have some varieties of aluminum wheels, then yes - the studs arent' long enough. For my stock steelies, I made it over the rotor & through the wheel with plenty of threads showing, no problem.
On the backing plate studs, well, if I could have gotten the old ones out without screwing up the housing I woulda replaced them with something longer BUT it works just fine as is.
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Old October 15th, 2009, 09:33
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CMAHON CMAHON is offline
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Re: Another Disc brake install

i did the same swap on my 01 and i didn't need to change the prop.
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  #9  
Old October 15th, 2009, 09:38
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Re: Another Disc brake install

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Originally Posted by CMAHON View Post
i did the same swap on my 01 and i didn't need to change the prop.
lucky you... i need it but cant find one at a yard... well i need to find a yard that will give me just the pvalve. or i could get it from the dealership for 90 bucks
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  #10  
Old October 15th, 2009, 10:03
Talyn Talyn is offline
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Re: Another Disc brake install

You don't NEED to change the prop valve, but changing it will work better with the discs. And you don't need to change the whole valve, just the internal spring. Try this guy for a used valve: http://www.daveysjeeps.com/

Last edited by Talyn; October 15th, 2009 at 10:07.
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  #11  
Old October 15th, 2009, 10:07
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Re: Another Disc brake install

Quote:
Originally Posted by CMAHON View Post
i did the same swap on my 01 and i didn't need to change the prop.
You should try putting the zj prop valve in and see if you feel any improvments... it may seem like you dont need it but I wouldnt be surprised if you saw improvement.
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  #12  
Old October 15th, 2009, 13:16
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xj_mike xj_mike is offline
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Re: Another Disc brake install

Actually someone on this board went through all the ways of using different prop valves and such and found what you need to change, to have the correct braking feel and max stopping power is to replace the internals of the XJ valve with the spring, internal plunger AND end cap from the ZJ.

I just found the post/pic relating to it.

http://naxja.org/forum/showthread.php?t=978214&page=2

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  #13  
Old October 15th, 2009, 13:49
srmitchell srmitchell is offline
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Re: Another Disc brake install

Cool. Really good info here. I hope to do the swap within the next few weeks.

Is it easy to pull the valve? And how much bleeding do you have to do when you change the zj valve?
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  #14  
Old October 15th, 2009, 15:01
multmigs multmigs is offline
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Re: Another Disc brake install

what did you end up doing about the E brake cables attaching to the ZJ lever things that stick out the back of the backing plate? I'm bout done collecting parts for this but I've seen both the liberty cables you mentioned before and the guys who have chopped the XJ cables and just secured them with a cable anchor type deal.... Otherwise this is a great pictorial on this stuff, and only thing it needs now is a complete parts list for NAPA etc...
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  #15  
Old October 15th, 2009, 17:53
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xj_mike xj_mike is offline
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Re: Another Disc brake install

I have also read that 2 pass. side Explorer cables work well but haven't seen it in person to confirm. YMMV
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