2wd to 4wd mj conversion

So I'll probably be helping my dad convert a 1989 MJ from 2wd to 4wd. He bought 2 cars at an estate sale and with the sale of the focus basically got the MJ for free. He's in Florida so it's a 2wd but its at least got the 4.0 motor and manual transmission. We are looking at doing the swap at christmas when I'm down there to help him. I know most of the XJ parts will swap over. plans are for maybe a 3" lift and some 33's. I'm looking for advice on what years we should be looking at for the axles. We don't have access to a welder so bolt on axles are preferred. based on what he'll do the Dana 30 front and Dana 35 rear will be okay. He's going to use it for the usual home depot runs and hitting some trails in florida so running in the sand. Bumper recommendations are also welcome. Thanks in advance for any advice.

Here's the pics he sent me and I convinced him that this built up is better than building up his H3


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Awesome. I have no idea what it takes to do the convert so I am deff interested. Good luck and keep us posted. :thumbup:

2014 JKUR

So you need NP231, HP30 (check to make sure gears match 3.55), front driveshaft, and transfer case shifter from 88-96 XJ.
97-98 should also work for front axle, but I would stay away from 99-01 as it might have a LP30
should be pretty straight forward, a buddy has done it a few times.

Thanks for pointing out the hp30. I'm actually recommending we do a gear swap to 4.10 to get some decent power with the 33's


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ok- then look for a 4 cylinder XJ, they are somewhat rare but out there. It will have 4.10 gears from the factory in the HP30.
Jeep TJ's with a 4 cylinder will also have 4.10's but will be a LP30.

pvanweelden said:

So you need NP231, HP30 (check to make sure gears match 3.55), front driveshaft, and transfer case shifter from 88-96 XJ.
97-98 should also work for front axle, but I would stay away from 99-01 as it might have a LP30
should be pretty straight forward, a buddy has done it a few times.

Click to expand...

Good list, don't forget the center console lever. There's already a hole on the floor.

I have the parts to convert my MJ. I need to get it done before winter !

Piginajeep if you get it done please let me know how it goes. I'm pumped about doing this with my dad since the last vehicle we built was my Tacoma in high school.


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You've got a good build list going. Highly recommend the 4.10's if you can. The 4.0 will pull 33's and 4.10's in the sand. May have to spank it a little bit, but it'll get the job done. I choose to drive the MJ over the JK most of the time. It's fun. Best of luck on the build.:yup:

pvanweelden said:

So you need NP231, HP30 (check to make sure gears match 3.55), front driveshaft, and transfer case shifter from 88-96 XJ.
97-98 should also work for front axle, but I would stay away from 99-01 as it might have a LP30
should be pretty straight forward, a buddy has done it a few times.

Click to expand...

You might want to check the transmission too...I'm not sure a 2wd transmission will mate up to a NP231 (I think it has to do with the output shaft length). You could convert it by swapping out some internals, but it might be easier to find a 4wd tranny from the junkyard to swap in and that might already have a NP231 bolted up to it.

EDIT: As for bumpers, I really like the JCR bumpers for the front. They have a DIY for the rear that might be nice to put on the MJ. They make most of my favorite addons for the XJ I drive.

Really Ty, Pig and Linebacker? Did you guys not remember that I'm in the process of doing the conversion to mine right now? Wth??

OP, you will need an AX15-4WD version transmission due to the tailshaft length. The floor shifter can be sourced for next to nothing, but make sure you get ALL of the linkage for it including the little shift lever that bolts to the t case as they are clocked differently for different vehicles. For example, the lever on a JK 231 is clocked different than an XJ and won't work.
The front axle won't be too hard to source provided you stick to a D30, anything bigger will take some creativity. I'm fitting JK D44's under mine and some modifying has to be done to make it work.
If you want to lift it, BEWARE, XJ lifts only agree with the front. XJ's are already "spring over axle" in the rear where the MJ is not. Also, your wheelbase is going to be longer than an XJ so all the cool stuff you see people doing to an XJ, such as coil conversion, won't work for you without some serious thought and modifications. I'm doing a Clayton long arm kit for my front with slightly longer shackles for the rear and 4:88 gears to run 35's.