1974CJ5 Posted January 26, 2009 Share Posted January 26, 2009 I currently have a 87 comanche "sport truck" w/ a 2.5, ax4, 3.55 gears. I love this truck, and it is really good shape. So I would like to retain it, but would also like it to be 4x4. I would like to go 4.0, since my truck is an 87 I should have enough engine bay correct? Should I stay with the 2.5 and just bore and stroke it? I would really like to have an ax15 tranny if I go 4.0. I believe these started in 1988 would this be compatible with my under body openings? I would like to have a an np231 transfer case as well any problem with that? Would the chrysler 8.25 rear end out of an XJ be suitable for an MJ? The donor vehicle for all of the above parts would be an XJ most likely. Any info that would prepare me for the job would be appreciated, or any suggestions for alternatives to these would be great. The whole drivetrain out of a 4.3 chevy blazer would be awesome but, am I to understand that the 4.3 is a little too tall for the engine bay? I am very sorry if the answers to all these questions have been answered but the search field kept telling me that it couldn't return any results. Thanks in advance. Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 26, 2009 Share Posted January 26, 2009 Welcome to the Club :cheers: Definitely go with the 4.0L as the 2.5L is not worth the effort or money for stroking. The firewall may need a "massage", but I think you are OK there. The AX-15 will work fine...and they started in mid 1989. 231 is fine. 8.25 will be ok, but you need to be sure to get the later model with the 29 spline shafts, but I forget the year for the change on those... :hmm: . A D44 would be better if you can find one. If you nave a complete donor vehicle, the swap should not be a real big deal. most everything is a bolt on change except the rear axle as you will have to weld new perches on for the MJ springs. Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 26, 2009 Author Share Posted January 26, 2009 are there aftermarket heavy duty spring perches for this application, or would I have retain the factory ones? I am not optimistic about finding a D44, would a ford 8.8 be okay if I was unable to find a later model 8.25? Link to comment Share on other sites More sharing options...
Pete M Posted January 26, 2009 Share Posted January 26, 2009 Personally, I'd find a 2.5L/AX-5/4x4 donor XJ and swap over the whole drivetrain to get overdrive and the 4.10 geared axles, but this all depends on what you want in the end. What are you looking to do in this truck? Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 26, 2009 Share Posted January 26, 2009 The 8.8 is a very desireable swap so yes, if you can get that it would be great. My preference on the perches are the ones from Rubicon Express, but buying some new stock perches would be fine. Depends on what axle you go with as to where you are going to need to get perches from though. Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 26, 2009 Author Share Posted January 26, 2009 Mostly daily driving, but probably 30% off road use. OX locker in the back, auto locker in the front w/ lockout conversion front axle is what I would like. I would probably lift it up enough to clear 31's-33's but I don't know about drive shaft angels :???: so that is probably a battle for another day. My off road plans for it would be fairly mild, just trail riding. I don't have the nerve to break stuff just to breaking it, or risk a rollover. I am not a very power hungry guy. Most of my wheelin' has been done in a 2.4 wrangler, and it has done everything I have wanted it to do, I have very rarely wished for more power, but have often been glad that I didn't have more power. When you do something stupid with very little power, you realize how bad it could have been if you had lots. Most of my want to go 4.0 stems from the fact that the 2.5 in my MJ feels like it has alot less power that my 2.4 in my tj (and it does). I would be happy if the truck felt like my 2.4 tj with an nsg370 and 3.73 gears. Since the early 4.0's made only marginally more power than 2.4 that is in my TJ, I felt that would be a good comparison. I have been under the impression that the aw4/5 trannys probably aren't strong enough for a locked rear end, but I would value countering opinions. Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 26, 2009 Share Posted January 26, 2009 You are correct...the AX4/5 tranny's are notoriously weak and should be kept to 95% DD & 5% easy trail. Driveline angles are not a worry in these trucks unless you are going more than 6-7" of lift. Go 3", throw some 31's on it and be done :thumbsup: I am in ageeement with your ideas of 4.0L, AX-15, 8.8 rear w/OX, D30 (non-disconect) front with Aussie or similar. :cheers: Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 26, 2009 Author Share Posted January 26, 2009 BLHTAZ I think I missed something: what does the "(non-disconect)" refer to the D30? The one that doesn't use vacuum motor correct? I had forgotten all about that, how will I know which is which? Is the motor housing pretty evident just looking at it? Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 26, 2009 Share Posted January 26, 2009 Yes, you are correct. The motor housing is very obvious on the right side rear of the axle tube where the control arms connect. There will be vacuum lines running to it. Link to comment Share on other sites More sharing options...
Pete M Posted January 26, 2009 Share Posted January 26, 2009 Your truck likely feels weak because of the 3.55 gears that are in the axle. Link to comment Share on other sites More sharing options...
mjeff87 Posted January 26, 2009 Share Posted January 26, 2009 I agree with Pete on gearing.....the 2.5 can't get enough. That said, you reach the point of diminishing returns with gears, heavy tires, and the TBI 2.5. Mine started just like yours, and has been a continual work in progress for the last several years (see sig). If you reallly wanna go 4.0/AX15, hit me backchannel and I can give you some tips. I just did this less than 6 months ago. Jeff Link to comment Share on other sites More sharing options...
pingpong Posted January 27, 2009 Share Posted January 27, 2009 A 4.3 fits fine in the xj/mj front end.. I know I have one :eek: and it is for sale as well :nuts: All you need is 3" of lift and Advance adapters frame mounts (around 190), along with the chevy drivetrain, and wiring. Anyway back on topic. I was Jeff's parts supplier when he did the swap. There are a lot of lil things that you will need that no one thinks about. It is best to get a whole rig and do the swap. I can't tell you how many times Jeff had to come back down, or called to ask me to check on something. OR you can sell your 4 popper one and buy one with a 4.0 Link to comment Share on other sites More sharing options...
bigd44889 Posted January 27, 2009 Share Posted January 27, 2009 y'all need to stop pickin on 4 popers i have 31's and have no problems power wise if i can get traction i can climb it 2.5 bored 40 over 4 speed 4:10 gears :fool: Link to comment Share on other sites More sharing options...
mvusse Posted January 27, 2009 Share Posted January 27, 2009 But if you ever go to WV, can you keep going 75 uphill? Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 27, 2009 Author Share Posted January 27, 2009 Thanks guys for all the info, and piece of mind. I believe I will start the search for an xj with most of the parts I want. I agree and would want the donor vehicle sitting right next to my MJ when I do the swap. I am intrigued about the chevy swap, especially since some of you guys have them, probably ultimately more trouble than the 4.0 right? Is there any particular year 4.0's that are more or less compatible, I am assuming I should shy away from OBDII engines. I have no hate for the 2.5 at all. Anymore when I come across a 4cyl with a timing chain rather than a belt, I am impressed. This little motor is currently doing everything my 2wd drive train is asking of it. I mean no disrespect to this engine. y'all need to stop pickin on 4 popers i have 31's and have no problems power wise if i can get traction i can climb it 2.5 bored 40 over 4 speed 4:10 gears :fool: Just out of curiosity: Did you get dyno tested before and after your bore up? I would just be cool to know. Link to comment Share on other sites More sharing options...
pingpong Posted January 27, 2009 Share Posted January 27, 2009 As to which swap is easier.. the 4.0 or the chevy 4.3. well that depends on what parts vehicle you have laying around. If I had a wrecked 4.3 blazer, s-10 or fullsize truck.. no real probelm there, but if i was to have to by stuff like adapters, wirning harness and stuff like that.. The 4.0 swap becomes cheaper Link to comment Share on other sites More sharing options...
Pete M Posted January 27, 2009 Share Posted January 27, 2009 Pretty much any year 4.0 will work fine since you'll be swapping everything from it: wiring, dash, drivetrain, etc. Make sure it all works well, the wiring isn't all hacked up, and corrosion isn't rampant in the electrical system. Link to comment Share on other sites More sharing options...
mjeff87 Posted January 27, 2009 Share Posted January 27, 2009 if you stay in the 87-90 renix era, you don't need to swap the interior/dash harness (at least, in my case I didn't). Just source an underhood harness and ECU and plug it up to your existing bulkhead connector @ the firewall. Mine was an 87 2.5/AX5 and I used an 87 Renix 4.0 along with an 89 MJ 4.0/AW4 engine harness and ECU. It eliminated the pesky C101 connector as well. Plugged it in and it fired right up...much to my surprise ;) Here's my semi-long winded writeup on my swap: viewtopic.php?f=7&t=11205&st=0&sk=t&sd=a Jeff Link to comment Share on other sites More sharing options...
bigd44889 Posted January 27, 2009 Share Posted January 27, 2009 no no dyno motor blew a rod went and got used block and started over as for 75 up hill in wv don't know havn't tryed but does fine job in northern ohio Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 27, 2009 Author Share Posted January 27, 2009 mjeff87 thanks for the link to your write up, I promptly bookmarked it, every minute of knowledge saves hours of cussing, and hundreds of dollars! Do you think that dodging added PIA of the interior/dash harness process is worth giving up the little bit of extra power found in the newer 4.0's? I was thinking of going with an 89 or so model xj anyway, I just wondered what your opinion was. The proper 89 model should provide me with a 4.0, an ax15, and a np231. Link to comment Share on other sites More sharing options...
Pete M Posted January 27, 2009 Share Posted January 27, 2009 Only late year 89s will have the AX-15. 1990s will work for you too as the HO came out in 91. Link to comment Share on other sites More sharing options...
mjeff87 Posted January 27, 2009 Share Posted January 27, 2009 I can't speak to the power difference between Renix and HO, but I can tell you that swapping the interior harness is not fun at all. It took me and Jerry about an hour just to get the interior stripped on the junkyard MJ I got the harness from, and we weren't being "gentle" about it.....if I were planning on reinstalling everything it would have taken quite a bit longer ;) I can tell you that the difference between the TBI 2.5 and the Renix 4.0 I swapped in is quite noticeable, and I'm very happy with the swap. Down-the-road plans for me include building a stroker and swapping it in at some point, but that stock engine has more than enough ooompfh for what I'll ever need. 4.56's with 33's, the thing was downright dangerous if you let it be. Jeff Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 29, 2009 Author Share Posted January 29, 2009 I can't speak to the power difference between Renix and HO, but I can tell you that swapping the interior harness is not fun at all. It took me and Jerry about an hour just to get the interior stripped on the junkyard MJ I got the harness from, and we weren't being "gentle" about it.....if I were planning on reinstalling everything it would have taken quite a bit longer ;) I can tell you that the difference between the TBI 2.5 and the Renix 4.0 I swapped in is quite noticeable, and I'm very happy with the swap. Down-the-road plans for me include building a stroker and swapping it in at some point, but that stock engine has more than enough ooompfh for what I'll ever need. 4.56's with 33's, the thing was downright dangerous if you let it be. Jeff Sounds like your really recall the swap quite well, and know your stuff. You will probably rue the day that you let me know that you did this swap already when I start hounding you with questions... since you and many others have been a huge help already, you guys have even got me down to what model year I am looking for. Thanks alot to all of you. :bowdown: Maybe one day you guys will start on a CJ and I can repay some of the help... Link to comment Share on other sites More sharing options...
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