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ZJ Disc brakes on a dana 35, wj booster, yj front lines

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Hello all and welcome to my information on how to disc brake swap and a couple other things. Let me start by sharing, mine is 1990 4.0 4x4 with auto trans. I have a Dana 35 rear. 


I would like to make this clear, I tried doing the disc swap to my 88 and it will not work as per these instructions. This how to is 1990+ c clip axles only. In order to fit this swap to non c clip, holes will need to be drilled for the backing plate to line up. Most importantly about the holes, I did not do it, but believe you will have to tweak the center for the bearing pressed axle shaft. For sure you will have to for the 4 holes that hold the backing plates. However the brake lines and the booster will still work. 


I first had to do my research, and then hope and stuff that it all worked out. It did. So here we shall start from front to rear!


I searched for a while to find the correct donor. I found a 97 zj that had been crashed, poor zj, it was nice. Moving on, I collected as much as I possibly could as to not have to buy any other stuff in addition to these parts. 


I pulled the proportioning valve, and the semi flex lines(I was dumb and forgot it the first time and had to go twice) the proportioning valve I received had only 4 lines from the zj, but a rear output with a brass fitting, which I was able to switch with a fitting from my mj. This fitting allows for a line that would otherwise have no place. The line to the front ties into the height adjusting stuff which I got rid of(we will talk about this more later) The zj lines are the ones i used, I had to adjust some in order to fit into the wj booster and master, the fittings all matched up between the wj master and the zj lines. The prop valve fit the same to the electric connection.


Lets now get into the wj booster. Came off an 01. This thing bothered me since there was little descriptions here. The electric clip on the master is of no matter ignore it. The wj booster simply does not line up the same, being there is a seam that it butts up against. A sawzall angled inward just slightly wider than the booster on each side will make for the appropriate relief points. I then used a hammer(I’m terrible and mean) to bend the seam between the incisions down and hit it with black rattle can to seal the cuts. Thankfully the vacuum line fits the same, though i did read a suggestion to use the plastic fitting off the original mj booster. I tried both and saw no difference. The studs are stupid long and take forever to tighten down, so I suppose you could make spacers to compensate some but I didn’t have a pile of washers available. The next thing about fitting the brake booster is something not well described, the difference in the plunger. By plunger I mean the washer on a stick part. This you need to do a few things to. The inner diameter has to get bigger. You need it to fit the washer that looks like a hat. This washer is essential in making the brake switch work. Next you can do one of two things, I did both. You take the outer edge of the washer plunger and you shave some material off, I used a Dremel for both widening the hole and shaving material off. Then the other option which I did, was to shave some material off the switch itself, I should have picked one or the other. The material to shave if you choose this route is opposite the electrical connectors. 


I sinply ordered yj front lines because I have only a 3” lift with a little flex, but the stock lines got taught when fully flexed. Simply fits right in, actually my drivers side didn’t quite line up and needed a little shaving on the edge where it butted up but works fine. Thanks dremel. 


Here we go! Onto the rear end! I went ahead and grabbed everything from the hard line back basically. As far as lines i started off at the single rear line, and attaches to the axle, before going to each side line. This helped to delete the height valve. Makes it simple if it’s simply not part of the circuit. I then really used each of the lines from there to the calipers. There were a couple things to line these up that don’t quite line up the same, but easy to just let hang, or bolt to axle. I used the e brake lines off the zj as well. This was as simple as switching them in and out as they match up well. My front line snapped after I set it all up, so I’ll need to see if it’s related later. Next, I kept all the parking brake pads and hardware which thankfully all worked alright. This made disassembly easy since the backing plate is held on by four bolts. I kept the calipers and rotors. They said the lug studs are longer on the disc brakes, they are correct. Since I’m lazy, I used the whole axle shafts which since I have a 90 meant easy bolt in. Anyways getting back to the topic, in order to swap the parts. You need to take off the drum cover and you can pretty much leave it at that. The Dana 35 features a fun bit with the differential. You will have to open it in order to swap. I discovered a fun 12 point 1/4” bit was required. You will see it on the gear set. I found it was easiest to remove the axle shafts by removing the right hand side 2 bolts over the gear set and the arched bracket holding it all together. Once you do so, the heavy metal pin through the middle of the gear set comes out. This allows you to push the axle shafts inward and pull the c clips. Try to keep the gears altogether as it’s not fun to put them all back together right in the middle. Once the axle shafts are out, you will see There are simply 4 nuts holding the drum assembly together. You should be able to remove the assembly at worst with some hammer persuasion. These studs can be pushed out and should be since they are just shorter(the disc backing plate is just a hair longer, but I destroyed mine off the donor so you can leave them with the drum ones). I had abs sensors on the donor parts, must be removed as it will not fit on the Comanche axle. Since I didn’t even unhook the lines from stuff, I made it much easier for myself, just pull off the Drums and line up the disc backs! Slide the back plates on, and boom 4 nuts on the studs and your good! Then slide the axle shafts back in, the ones with the longer studs of course! C clips on, bolt back in, 12 point 1/4” tight to hold the big steel bolt in place, you can now seal this up. Remainder of reassembly comes in by simply putting the rotors on, calipers on, thankfully my pads were like new, and doing the bleeding. As with all bleeding when doing new lines, you should start with the furthest line, the rear passenger side, then rear drivers, the passenger front, and then drivers front. I had only a cheap vacuum helper at first. Thankfully my wife is awesome and helped me bleed them proper. Another little note. Label which side you remove things from just in the off chance everything decides they liked being on one side or the other. 


I very much so apologize for lack for lack of pictures and really hope I made up for things in description. I’ve attached as many pics as I got which sucks because I should and could have taken more. Also if I need to change anything due to typos or mistakes or things not making sense help me. I want to help it all make sense since I found very mixed info when I researched! 














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