MJ 4WD Conversion

[utahmj]

Hey guys, I am starting to ponder what to do with the MJ I just picked up. It is a 1989 4.0 with 123k original miles, I bought it from the original owner for $1700. The downside is it is 2WD. I bought it with the intentions of swapping it to 4WD but after doing alot of research I am wondering if it is all really worth it and wanted to get your guys thoughts/opinions. After reading various forums and watching videos I am finding some people say it is not bad to do the swap and there are some that say it is not worth the time/headache to do it. So far I have not found a step by step forum or video of anyone doing this on an MJ but I have seen quite a few on XJ's which from what I understand is the same thing besides the rear drive shaft really. What I am wondering is if these guys that are saying it is pretty "easy" are full time mechanics and have access to all the necessary things to make it easy like power tools and lifts. I would by no means say I am a mechanic but I am not afraid to get the job done, I do not have a access to a lift and I have basic tools, more then just sockets and screw drivers but pretty basic tools. Part of my plan was to Daily Drive this truck, and to sell my current 2008 F-150 mainly because I want a truck that is paid off and I do not pull or haul anything (Plus I've always thought Comanches were bada**) Realistically if I did find a decent donor XJ or got all the parts together is this something I could bust out in a weekend or is it going to be a more complicated project taking weeks? I would have my ZJ to drive as a back up  but I could not be out of my DD for weeks. Is this really going to be worth the time and money and possible complications down the road?  Or did I pull the trigger too soon and should just wait for a 4x4 to come along? Side note, it does not have A/C which I am starting to realize blows, would converting an A/C system also be a huge pain the the a** and may also just be worth just finding one with it already? Sorry for the novel guys but I am really starting to wonder if this will all really be worth it. Any help would be appreciate especially from those who have personally done the swap. Thanks guys. 

[gogmorgo]

It's not a particularly complicated conversion, but it's not a small project either. You are pulling and replacing the front axle and transmission to do it, after all.

Arguably though you don't need to do it all at once. You can do the axle one weekend, transmission the next, sort of thing, without affecting the ability to take it to work. 

 

[Dzimm]

It's not as difficult as is sounds, just time consuming.  Like gogmorgo said though, do pieces at a time if you have to.  

 

Find a donor XJ and pull everything you'll need, front axle, transmission, front dirveshaft, shifter, linkages, ECT. 

 

The real hangup will be a rear driveshaft.  You can either find one from a 4x4 MJ with the same engine, trans, and bed length.  You could also have one modified, or have one made from scratch.  I had the rear shaft modified and the front one rebuilt for my 97+ truck and it took about a week and a half before I got them back so keep that in mind.

 

As far as doing it with basic tools, I realized anything can be done on these trucks with basic tools.  I did a full 97+ swap with an angle grinder and a simple socket set.  Borrowed a welder for my rear axle swap and had to buy an electric impact to swap a flexplate but otherwise it was all hand tools.

 

Don't be afraid of this swap, do your research and you'll know pretty well what you are doing going into it.  Finding a 4x4 MJ would potentially be easier but how often do they come up for sale in your area for a decent price?

 

As for the AC swap, whatever donor XJ you get, just pull everything from it and you'll be good.  It's a much more involved process though as you'll have to pull the dash to get at the hvac box.  Find a cheap XJ with the goodies you want and buy it to steal the parts from for both the 4x4 conversion and the AC.

[Pete M]

quick question, do you need 4wd for anything in your daily drive?

[utahmj]

1 hour ago, gogmorgo said:

It's not a particularly complicated conversion, but it's not a small project either. You are pulling and replacing the front axle and transmission to do it, after all.

Arguably though you don't need to do it all at once. You can do the axle one weekend, transmission the next, sort of thing, without affecting the ability to take it to work. 

 

Could I swap the front axle to a XJ D30 and still drive around without it hooked up to a transfer case? Also would any XJ D30 be the same gear ratio as my stock MJ rear axle? 

[utahmj]

1 hour ago, Dzimm said:

It's not as difficult as is sounds, just time consuming.  Like gogmorgo said though, do pieces at a time if you have to.  

 

Find a donor XJ and pull everything you'll need, front axle, transmission, front dirveshaft, shifter, linkages, ECT. 

 

The real hangup will be a rear driveshaft.  You can either find one from a 4x4 MJ with the same engine, trans, and bed length.  You could also have one modified, or have one made from scratch.  I had the rear shaft modified and the front one rebuilt for my 97+ truck and it took about a week and a half before I got them back so keep that in mind.

 

As far as doing it with basic tools, I realized anything can be done on these trucks with basic tools.  I did a full 97+ swap with an angle grinder and a simple socket set.  Borrowed a welder for my rear axle swap and had to buy an electric impact to swap a flexplate but otherwise it was all hand tools.

 

Don't be afraid of this swap, do your research and you'll know pretty well what you are doing going into it.  Finding a 4x4 MJ would potentially be easier but how often do they come up for sale in your area for a decent price?

 

As for the AC swap, whatever donor XJ you get, just pull everything from it and you'll be good.  It's a much more involved process though as you'll have to pull the dash to get at the hvac box.  Find a cheap XJ with the goodies you want and buy it to steal the parts from for both the 4x4 conversion and the AC.

That makes me feel a bit better. MJs are super rare in my area which is why I pulled the trigger so quick on this one, and I feel like a decent donor XJ is too. So far I have not had much luck finding a manual that doesn’t have a ton of miles on it. I could find a great donor with a auto all day long, but I would really like to stick with the manual. Maybe it’s worth it to just convert it to auto as well? 

[utahmj]

13 minutes ago, Pete M said:

quick question, do you need 4wd for anything in your daily drive?

I guess it would not make it or break it on my daily drive, the snow here in Utah can get pretty bad, but I could drive the Zj on a bad snow day. The Mj would be my daily but I would still like a 4wd to play on the weekends and to make it the Jeep it should be. 

[Dzimm]

12 minutes ago, utahmj said:

I guess it would not make it or break it on my daily drive, the snow here in Utah can get pretty bad, but I could drive the Zj on a bad snow day. The Mj would be my daily but I would still like a 4wd to play on the weekends and to make it the Jeep it should be. 

I would avoid driving an MJ on a bad day regardless but that's just me.  

 

A donor with a manual will be more difficult to find.  You may just need to find a 4x4 manual trans separate from the parts XJ.  The donor XJ doesn't necessarily need to be decent.  It can be wrecked, rusted out, not running, ECT.  The cheaper you can get it the better as long as it has what you need on it.

[Pete M]

what's your budget?  planning on any lift or bigger tires?

[Eagle]

Is your current daily driver 2WD or 4WD? If it's 2WD and you're happy with it, then you don't need to convert the MJ to 4WD. If your current daily driver is 4WD and you'll miss it, then convert.

 

FWIW, I put a Truetrac gear-driven limited slip differential in the rear axle of my '88 MJ. I live in Connecticut, we get snow and ice, and there's a steep hill at the end of my road. With the Truetrac, I almost never had to use 4WD on the street -- I had 4WD for off-roading. If I had carried a bed box with a hundred pounds of mason's sand in it during the winter, I absolutely would not have needed 4WD during the winter.

[Eagle]

52 minutes ago, utahmj said:

Could I swap the front axle to a XJ D30 and still drive around without it hooked up to a transfer case?

 

Yes.

 

Quote

Also would any XJ D30 be the same gear ratio as my stock MJ rear axle? 

 

No.

[Pete M]

just for clarification (depending on what answer you were looking for): would ANY xj front axle ratio match? no.  are there SOME xj axles that would match?  yes.  Problem is that your current ratio is likely 3.07 and that ratio sucks.   

 

my suggestion is to keep reading.   there's a ton of experience and opinions on the CC.  absorb all you can.   Then formulate a plan.  figure out what it is you want and how to get there from here.  Keep in mind that old parts are old parts.  even the newest XJ is pushing 20 years old now.  Being able to test drive a potential parts XJ is a plus (over a pile of question marks that you have to tow home).  buying a rebuilt trans is also a plus (vs one with 200k on it).  finding OEM parts is a plus (chinese parts can ruin your day).  etc.

 

my ultimate DD build:

4.0 with AC

rebuilt AX-15 with external slave

late model dana 30 with 4.10s

late modal 8.25 or 44 or 8.8 with 4.10s

late model 242 t-case with the sealed rear output

complete and quality 3" lift

31" tires

 

[utahmj]

2 hours ago, Eagle said:

Is your current daily driver 2WD or 4WD? If it's 2WD and you're happy with it, then you don't need to convert the MJ to 4WD. If your current daily driver is 4WD and you'll miss it, then convert.

 

FWIW, I put a Truetrac gear-driven limited slip differential in the rear axle of my '88 MJ. I live in Connecticut, we get snow and ice, and there's a steep hill at the end of my road. With the Truetrac, I almost never had to use 4WD on the street -- I had 4WD for off-roading. If I had carried a bed box with a hundred pounds of mason's sand in it during the winter, I absolutely would not have needed 4WD during the winter.

My current DD is a F-150 with 4wd if I'm honest I did not use the 4wd all too often maybe a couple of times but it did pretty good without weight in the back. Honestly it sounds more appealing to do what you did and put a true Trac in there then to do the whole swap. I will have to do some more research. 

[utahmj]

2 hours ago, Pete M said:

just for clarification (depending on what answer you were looking for): would ANY xj front axle ratio match? no.  are there SOME xj axles that would match?  yes.  Problem is that your current ratio is likely 3.07 and that ratio sucks.   

 

my suggestion is to keep reading.   there's a ton of experience and opinions on the CC.  absorb all you can.   Then formulate a plan.  figure out what it is you want and how to get there from here.  Keep in mind that old parts are old parts.  even the newest XJ is pushing 20 years old now.  Being able to test drive a potential parts XJ is a plus (over a pile of question marks that you have to tow home).  buying a rebuilt trans is also a plus (vs one with 200k on it).  finding OEM parts is a plus (chinese parts can ruin your day).  etc.

 

my ultimate DD build:

4.0 with AC

rebuilt AX-15 with external slave

late model dana 30 with 4.10s

late modal 8.25 or 44 or 8.8 with 4.10s

late model 242 t-case with the sealed rear output

complete and quality 3" lift

31" tires

 

 Ideally that would be my perfect DD as well. I am just wondering if it is really going to be worth my time and effort to get it all done. I think it would really test my patience lol. I will absorb all the info I can and come up with a game plan, heck I may just try and do a True Trac dif like Eagle did. Thanks for all this info I appreciate it! 

[omega_rugal]

i assume your mj is automatic,

 

4.0+auto  = 3.55 gears

 

any 4.0+auto xj donor will have the right front diff, those are plenty

[utahmj]

4 hours ago, omega_rugal said:

i assume your mj is automatic,

 

4.0+auto  = 3.55 gears

 

any 4.0+auto xj donor will have the right front diff, those are plenty

Mine is a manual. I see yours is 2wd have you had any issues in the snow?

[Pete M]

snow tires are more important than 4wd  

[Egm89]

Not hijacking this treat or anything, but at topic at hand its actually not that hard if you take your time to do the research and not just here at CC, but also at Naxja etc etc.

And I'm saying this because I think I'm on the same boat as you are my friend, mine its also a 4.0 2wd trying to convert it to a 4wd very close to Pete's specs actually. And not an accomplished mechanic or anything but this truck are so straight forward (not counting electronics; those are a PITA) that after all month of research I decided to pull the trigger on parts.

 

Ax15 94+ come with the external slave (you want that trust me)

And the transmission thing that volts into it (forgot the name) you need that aswell.

 

Come on man! Lets do it 

 

[gogmorgo]

3 hours ago, utahmj said:

Could I swap the front axle to a XJ D30 and still drive around without it hooked up to a transfer case? Also would any XJ D30 be the same gear ratio as my stock MJ rear axle? 

Yes and not necessarily. 

Running with no driveshaft is essentially the same as being in 2wd. It would only ever be an issue if you've got a full-time transfer case with no 2wd or locked centre diff, but that's not the case with any factory XJ/MJ tcase, and definitely not a concern without one.

 

To answer the other question, if you find a stock XJ donor with the same engine/trans combo, it probably has the same gear ratio, but it's not a 100% guarantee. Maybe 98%. On the other hand if you find a matching d30 and c8.25 out of a 97+ XJ it's not a big job to weld perches onto the rear axle and it's going to be an upgrade, not that there's anything wrong with a d35 in a daily driver. Unless you're lucky enough to already have a Dana 44, but that's unlikely. 

 

As far as truetracs go, I've got one in my zj (4.0/ax15/np231/d35) and yeah, it's pretty much the $#!&. Traction when I need it without my input, almost imperceptible on the street, and it doesn't clunk or slam together like an auto-locker. When I put it in all I did was reuse all the shims off the old carrier, and the gear pattern was good enough to run. But also before the truetrac went in I swapped on a decent set of winter-rated ATs and went from almost requiring 4x4 to get around town to 2wd and open diff and no problems. I've also got a 2.5L 2wd shortbed MJ that gets around okay with an open diff and mediocre winter tires, although I do need to be more careful about where I park than something with 4x4. 

As Pete said, 4x4 is great, but proper winter tires will get just as far as 4x4 and non-winters if you're only planning on staying on maintained roads. I don't know what winter's like in your area, but our last snowfall is typically mid June and the first will be early September... mountains and whatnot. That's not to say though that the combination of winter tires and 4x4 isn't a pretty big deal. 

 

[omega_rugal]

1 hour ago, utahmj said:

Mine is a manual. I see yours is 2wd have you had any issues in the snow?

 

uhh then you are in trouble, 3.07s front diff are rare, you gonna have to swap both axles

 

snow? what´s that?............ really where i live i hace seen snow 3 times in my entire life, but i have driven the MJ in mud, with small chains for better traction with no problem...