Jeep MJ project, guidance needed

[RusellFromCanada]

Hello, first off I apologize if I'm posting in the wrong place. I have used multiple jeep forums for other builds in the past but this one will be pretty involved and I figure I could use some direct input from you guys. This is MY first forum post ever.

 

So, I've bought myself a 4.0L 1987 2wd short box comanche with 257,000km for $1000 (how could I resist joining the club) The truck needs a new clutch (I believe/was told) to drive. I've gathered a few parts a couple days ago, those being

-hood

-front bumper

-drivers door

-ax-15 transmission

-transfer case (231? maybe? can't remember but the splines are the same)

-front driveshaft

-short bed rear driveshaft (possibly a 4x4 AUTO shaft he wasnt sure and neither am i)

-floor pan

-tailgate

 

Plans for the truck: Obviously i intend to do a 4wd swap. I figured if I'm dropping the transmission to service the clutch i may as well dive into the 4x4 swap sooner than later. there are some diffs out of a 91 comanche for sale in my area that i intend to pickup in the following days. This is not intended to be a dedicated offroad rig, i have a TJ for that. I'm hoping to maybe daily it, but mostly want it for camping, hauling dirtbikes, light offroad ie mud roads, rocks but nothing serious, and of course breaking necks.

 

So here's my questions i'm hoping you guy's can help with

-will the 91 axles be the same as my 87?

-if the rear driveshaft is from an auto will it require modification?

-what gear ratio would be ideal for 31's? (my rear axle is 3.08 currently)

-what gear ratio would be ideal for 33's? (haven't decided on size yet)

-I need to buy a center console with the added transfer case shifter. Are the auto/manual consoles the same?

-will a xj windshield fit in without modification? Is this a do-able diy job? i've replaced a couple windshields at work before but on army trucks. nothing like this.

-i have a set of 33x12.5r15 tires/wheels. are these an option or should i stick to the 10.5's

-what all do i need to modify if i decide to lift for 33's? would it be reasonable to daily? would you recommend a cheap lift or new everything?

 

 

I'll try and upload some pictures as soon as i can. Bear with me here lol. Thanks for any input you guys have for me.

[Pete M]

-will the 91 axles be the same as my 87?    -------the axles should bolt in.   don't assume that the brakes or bearings are the same though, so be sure to buy parts for a 91 axle.

 

-if the rear driveshaft is from an auto will it require modification?    ---------given the same engine and rear axle, the auto shaft will be about 1" shorter because the auto trans is 1" longer.  the link in my signature has a link with the chart of all the different shaft lengths.

 

-what gear ratio would be ideal for 31's? (my rear axle is 3.08 currently)     ---------I prefer 4.10s, but there's a range of what can work.

 

-what gear ratio would be ideal for 33's? (haven't decided on size yet)    ---------I prefer 4.88s, but again, there's a range of what can work depending on what you plan to do with it.

 

-I need to buy a center console with the added transfer case shifter. Are the auto/manual consoles the same?   --------- I wanna say yes, but the center bit (aka the boot) will be different.

 

-will a xj windshield fit in without modification? Is this a do-able diy job? i've replaced a couple windshields at work before but on army trucks. nothing like this.  --------all XJs/MJs share the same windshield.  the 97+ rubber windshield trim can be used on older Jeeps.   it's a job I would gladly pay a pro to do.  especially since it isn't all that much money.

 

-i have a set of 33x12.5r15 tires/wheels. are these an option or should i stick to the 10.5's   all depends on what you plan to do with the truck.

 

-what all do i need to modify if i decide to lift for 33's? would it be reasonable to daily? would you recommend a cheap lift or new everything?     -----unfortunately pretty much anything you do to the truck will make it a worse daily driver than stock.  MPGs get worse, steering gets worse, acceleration gets worse, braking gets worse, noise gets worse, everything measurable gets worse.  the question is where is the cutoff line for you.   everyone's commutes are different, everyone's tolerances for a old truck are different. 

[RusellFromCanada]

That response was a ton of help, thank you Pete.

[89 MJ]

I have 4.10s on 31is in my truck. When it comes to needing tires, I plan on going with a 33 because I feel like I am turning too many RPMs in 5th gear. 60 is about 2200 and 70 is about 2550. I wish I would have gone with 3.73 gears in mine. 
 

Even for towing, I feel like I have too much gear. I have towed well over 1000 pounds many times and I feel like I have more heating than I need even then. 
 

My biggest complaint though about having 4.10s and 31s is how short 1st gear is. I don’t even make it half way through an intersection before needing to shift. I use 2nd gear to start moving most of the time. 
 

With all that being said, I also get around 16 mpg with mixed city and country driving and the pep of the 4.10s is nice. 

[Pete M]

it's more than you may be accustomed too.     just think about the rpms of the 2.5L/auto with its 4.56s and 195 tires.

[eaglescout526]

42 minutes ago, 89 MJ said:

My biggest complaint though about having 4.10s and 31s is how short 1st gear is. I don’t even make it half way through an intersection before needing to shift. I use 2nd gear to start moving most of the time.

That’s a whole other thing when driving a 2.5L. I shift two times before leaving intersection. 

[Pete M]

also, there's nothing wrong with starting in second.  it's not like there are rules about always having to start in first.   you'll love that extra leverage of first every time you're hauling anything heavy.

 

also, also, if I remember right, 3.73s and 31s are the exact same as 3.07s on stock tires so 4.10s is only 1 step up from that (and the rule of thumb is that you want to go one step more to accommodate the extra weight of the bigger tires.)

[OldManComanche]

Why don't you get it running, and then see what you have to work with and go from there.

Good Luck!

[JMO413]

Welcome to the club. Mine is 31's and 4.10. IMHO it's the perfect ratio. I also don't mind shifting half way through the intersection. The combo is also perfect for a DD. Enough to go most places and still nice to drive. 

 

Don't forget to fill out your signature.

 

[JustEmptyEveryPocket]

Wait, are you all trying to tell me you shift BEFORE your tach reaches that red line? I thought the red line was the upshift indicator? Might explain why I'm only in 3rd gear and at 75mph.....

 

Joking aside, the manual transmission and 4.10s on 31" tires is a great combination. DD material for sure.

[dasbulliwagen]

If youre lifting more than 3 inches, a set of control arm drop brackets will help greatly with ride quality. Also, don't cheap out on shocks. I'm at around 6 inches with drop brackets, adjustable control arms, and Bilstein 5100 shocks, it rides almost like stock, which is exactly what I was going for. And keep your sway bar. Lots of guys say it isnt necessary, but if youre on road dailying, its a good idea to keep it. Add disconnects to it if you want to, but keep it. Upgrades are also easily available from other models to give an even better on road feel while cornering. 

[watchamakalit]

3 minutes ago, dasbulliwagen said:

If youre lifting more than 3 inches, a set of control arm drop brackets will help greatly with ride quality. Also, don't cheap out on shocks. I'm at around 6 inches with drop brackets, adjustable control arms, and Bilstein 5100 shocks, it rides almost like stock, which is exactly what I was going for. And keep your sway bar. Lots of guys say it isnt necessary, but if youre on road dailying, its a good idea to keep it. Add disconnects to it if you want to, but keep it. Upgrades are also easily available from other models to give an even better on road feel while cornering. 

I agree with all of this. With the addition that drop brackets arent the only option. The same objective can be achieved with proper control arms. Shocks are important! 

[ghetdjc320]

I’d also suggest running 31’s with maybe a very mild or no lift. 33’s require quite a bit more work.

[RusellFromCanada]

Ok. I will plan on staying with 31's with no lift, atleast until i get my mj on the road.

 

I found an XJ with 3.55 gears, would this be a worthwhile swap for my 3.08's? How much trouble will it be to mount the rear axle? I'm of the understanding these do NOT bolt in. Could someone explain?

 

Also, I have the bench seat in my truck, i need to find a t-case linkage as well as the console with the t-case controls. Can i take this from any xj? theres a 1990 xj auto with bucket seats in my local scrap yard. I'm not sure how the fitment will work with the bench seat and am having a hard time finding the info i need if someone could steer me in the right direction. Thanks.

[Pete M]

XJ leaf perches are in the wrong place.  you'll need to put some in the MJ location.   

 

and anything is better than the 3.08s.  

 

benches would have a smaller console than XJs got.  I've seen people use a 4banger TJ console.  it even has a cupholder  

 

does you bench have the center cutout like the one in this pic?  or is it straight across on the front edge?

 

 

[eaglescout526]

I took a bad shape XJ full console and cut it in half and installed the side mount cup holders. 

[ghetdjc320]

2 hours ago, Pete M said:

XJ leaf perches are in the wrong place.  you'll need to put some in the MJ location.   

 

and anything is better than the 3.08s.  

 

benches would have a smaller console than XJs got.  I've seen people use a 4banger TJ console.  it even has a cupholder  

 

does you bench have the center cutout like the one in this pic?  or is it straight across on the front edge?

 

 

Very interesting pic. Wonder if the full TJ console would fit with buckets. 

[kryptronic]

On 8/25/2021 at 12:03 AM, Pete M said:

also, also, if I remember right, 3.73s and 31s are the exact same as 3.07s on stock tires

 

This is correct for 4.0L manuals, and why I recommend 3.73 with 31s with thqt setup.

[89 MJ]

As someone that has 4.10s and 31s, I would recommend trying to find a set of 3.73 axles. 

[RusellFromCanada]

Ok. I'll pass on the 3.55's and wait for 3.73's or 4.10's. Hopefully 3.73's as I do a lot of highway and don't plan on hitting many trails. My seat has the little cutout like the one pictured. Does the xj console cut in half look decent? Or does it look like a cut in half console lol. I'm open to whatever suggestions. That TJ console looks pretty nice. I want an OEM look.

 

I've completely unbolted the transmission from the engine, but haven't mustered the courage to pull it. I don't have a tranny jack. Anyone tried muscling one out before? Or recommend any tricks? A floor jack and prayers are the plan for now but I won't be back home to pull it for a few days now so I'll take whatever advice I can get until then

 

Thanks a ton for all the help/advice guys.

 

 

[Pete M]

transmission jacks aren't all that much from Harbor Freight.  

[rylee144]

I used a floor jack and a buddy to hold it old there as it was lowered. Worked fine. Took two of us to lift the new one back into position as we couldnt get the angle right on the jack

[RusellFromCanada]

I'm very cheap lol. I just realized I have a friend with a motorcycle jack though which should work fine.

[watchamakalit]

Floor jack and alot of cussing is my prefered method. Lmao

[dasbulliwagen]

As for transfer case shifter, youll need one that came from a vehicle with the same transfer case as yours, so that the linkages are the correct length. youll need the body side bracket as well to support the cross bar, don't forget that.