Converting 1987 MJ longbed from 2wd to 4wd

[Kesswic]

All,

 

I just recently got a Comanche as my first car and want to upgrade it. The truck itself runs smoothly and only only has minor problems associated with its age. While driving it the past few months, I've noticed how far behind it is compared to other trucks and wanted to upgrade it so I can drive safer and be able to take if off road. The first thing that I have to do is convert it to 4wd.

 

I have no clue how to do this. This is my first "real" project and I don't have a lot of experience upgrading jeeps, but I want to learn. What is the best way to convert it? I've been told that the easiest way is to buy a doner XJ of the same year and put my MJ frame on the XJ chassis. Is that true?

 

What would y'all recommend that I do? What should I research? What's the best method? How should I prepare for it? How much would it cost?

 

Thank you for your patience

[89 MJ]

21 minutes ago, Kesswic said:

What is the best way to convert it? I've been told that the easiest way is to buy a doner XJ of the same year and put my MJ frame on the XJ chassis. Is that true?

 

What would y'all recommend that I do? What should I research? What's the best method? How should I prepare for it? How much would it cost?

 

Thank you for your patience

I have some quick questions before I go about answering your questions. Is your truck a 5 speed or an automatic? The only 5 speeds that came in MJs were manuals. 

 

Yes, the easiest way would be to buy a similar year XJ (I'd look for an 87-90 because you have a Renix truck) and then swap the transmission/transfer case/front driveshaft/front axle into your MJ. Then you will only need to get your stock rear driveshaft shortened (~1 foot if I remember right). I will link some threads that cover this for you. 

[derf]

The easiest way to do it is to find an Cherokee or Comanche donor vehicle.  The Cherokee and Comanche have the same drivetrain and swapping that is "easy".  Find one with the same engine and transmission as the one you have now.

 

There are some changes to the vehicles as you go from year to year.  The big change from first gen "Renix" (Renault/Bendix) fuel injection to Mopar or "H.O." injection happened between 1990 and 1991.  Best bet is another 87.  But 87-90 is "easy".  For those years, you only need the transmission and transfer case, along with other bits.  If you get a 91 or newer, you can still do the swap but you will want to swap the whole engine, transmission, and transfer case along with all of the wiring.  A lot of little things changed like the intake manifold and some other things so it's easier just to grab the whole engine but it will bolt right in.

 

The transmissions are the same except at the very back.  The 2WD and 4WD versions have unique tail shafts.  It's a matter of just dropping the transmission and installing the replacement.  A rebuild while it's out may be a good idea.  Once the 4WD transmission is in, the transfer case bolts up.  The front axle from the donor would bolt in with no modification but you absolutely must ensure that the gear ratios in the front and rear axle match or you break things in 4WD.  The front driveshaft from the donor will bolt in (replace the u-joints while it's out) but you may need to modify the length of your rear driveshaft.  If you have a Cherokee donor the rear driveshaft is too short.  Any drivetrain shop can shorten your original driveshaft to fit.

 

There are many opportunities to do some upgrades as you go.  Some are more "important" to do than others.  There are plenty of threads on here talking about them.  Spend a bunch of time looking around here and be sure to ask plenty of questions.

[89 MJ]

Here are 2 threads that have done 4x4 swaps. Both of these guys did the swap well if I remember correct.

[89 MJ]

Why do you want a 4wd truck?

 

Also, @Pete M, should this be moved over to tech questions to get more eyes on itS?

[mjeff87]

OP, whereabouts are you in "Virginia"?  I'm in the Richmond area.....I can give you some good input if you're local.  There's a few great junkyards around here that you can source parts from for this project.

[Kesswic]

On 10/6/2020 at 8:55 AM, 89 MJ said:

Why do you want a 4wd truck?

 

Also, @Pete M, should this be moved over to tech questions to get more eyes on itS?

I would like to put better axles on it and put bigger tires on it for starters. The main reason is so I can have better braking control. I don't know about other MJ's, but mine uses drum brakes, and I've slipped right through red lights and intersections because my brakes lock. Making it safer for me to drive is what I'm looking for right now, and 4wd and new brakes would help me with that.

[89 MJ]

57 minutes ago, Kesswic said:

I would like to put better axles on it and put bigger tires on it for starters. The main reason is so I can have better braking control. I don't know about other MJ's, but mine uses drum brakes, and I've slipped right through red lights and intersections because my brakes lock. Making it safer for me to drive is what I'm looking for right now, and 4wd and new brakes would help me with that.

4wd and 2wd have the same brakes. I understand wanting bigger tires though.