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View Full Version : '88 231 in a '97 Grand-- the swap saga



rccolacc
06-21-2005, 08:48 PM
I’m not sure I posted this in the right forum. I know the 231 swap has already been written about several times, but I thought I’d share some things not covered in those articles.
Sorry for my really long post, but I just want to be thorough and clear.
I bought a ’97 Jeep Grand Cherokee in October with a bad viscous coupler on the NP249 (got a sweet deal too because the dealer thought it the Jeep was junk). I’ve been driving around the Jeep with no front driveshaft for the past 9 months while I come up with a NP 231 to put in it.
Over Christmas I bought an ’88 231 that came out of a Jeep Cherokee. It had a 21 spline input shaft, so I pulled the input shaft and planetary gearset out of my 249 and put it in the 231 and installed the whole thing. I realized the gear cut was different between the two input shafts, but I read somewhere (Carl aka Swampy) that as long as you swapped the whole planetary, it would work. It looked beautiful and fit fine, but upon driving it down the street, I noticed it had a loud roaring sound at any speed greater than 10 mph. I replaced a bearing in the tailhousing thinking it was that, but nothing worked. I was forced to put the 249 back in it.
A few months later I bought a 23 spline input shaft from a guy that had it in his 94 Grand Cherokee. I figured it should work since the ’94 shaft was from the early gear cut and so was my case. I put the whole case together, and the other day attempted to swap it in to my Grand. Wouldn’t you know, but it would not fit! The shaft slid over the transmission splines, and the studs went in their holes, but the case was .25” from going all the way on to the transmission. After removing the 231 and comparing it to my 249, I could see the input shafts were different. They were both 23 spline, and they both were the same length coming out of the case, but the ‘94 had a collar on the inside preventing the transmission shaft from sliding all the way in (see cut-away diagram). I’m putting it on a lathe tomorrow here at school to machine out that collar so the transmission will fit all the way in. Hopefully the third time I install this it will work.
The lesson learned from this swap is get the right year transfer case or you end up working a lot to get it to fit. I should have bought a 95 or newer case and swapped it in. That way my 97 input shaft would fit right on and not make noise.
I also would like to add that I’m getting pretty good at taking apart the 231 and putting it back together. I think I’ve RTVed the case halves together 5 times in the past 6 months doing this swap. I’m also getting pretty good at swapping the transfer case. I pulled the 249, installed the 231, pulled it back off and put back on the 249 in 3 hours this past time. All in a dorm parking lot too! I just hope this next time I do it, it’s the last time.
Does anyone have any reason to think milling out the collar would be a bad idea? Is there anything else I need to do to this 231 to make it work in my 97? I know about the speedo sensor and the 4wd indicator. I just don’t want to install it a 3rd time and learn something else about input shafts and gear cuts.
Thanks for the help.
-RC

http://img.photobucket.com/albums/v409/rccolacc/94.jpg
http://img.photobucket.com/albums/v409/rccolacc/97.jpg

RiPPiNiTuP7
06-22-2005, 12:23 PM
i ran into the same problem you did with that little collar inside the input shaft. i was lucky because all i had to do was take the input shaft from my 249 and install it in the 231 and i was good to go. i don't see why you couldn't grind that collar down, but it seems like it would be a huge PITA getting it done.

rccolacc
06-22-2005, 05:30 PM
I got the input shaft machined out today. The collar is gone, so now hopefully everything will fit right when I try to put the case on the back of the transmission. I'll reassemble the whole thing and try to install it next week at some point. I'll report again on if it works.
You're right-- it is a pain to go through all this trouble to make it work. I'm just glad it's only costing time and not (much) money!
-RC

ATL ZJ
06-22-2005, 08:17 PM
I got the input shaft machined out today. The collar is gone, so now hopefully everything will fit right when I try to put the case on the back of the transmission. I'll reassemble the whole thing and try to install it next week at some point. I'll report again on if it works.
You're right-- it is a pain to go through all this trouble to make it work. I'm just glad it's only costing time and not (much) money!
-RC

Good luck with it man, you'll enjoy the 231 over the 249 for sure though.

rccolacc
09-12-2005, 03:49 AM
Finally, after procrastinating the swap, I've done it. The '88 231 is officially in and working in my '97 ZJ. I got the input shaft milled out from that 94 ZJ, and after putting it together and installing it, it works. I drove it around the block and down the highway, and everything feels good. No grinding noises like last time. Guess the gear pitch change really did make a difference. I'm so excited now to really have 4x4 I can take out of 4x4. No more of that 249 with the bad viscous coupler.
Just wanted to make it known that it worked, even though it took a lot of work.
-RC

gonecheenin
09-26-2005, 09:00 AM
I just ran into that "collar" deal myself this weekend during my Manual tranny swap

the 242 out of my 42RE equipped 95' Grand has what i believe to be the 23 spline med. length input gear and it will slide right onto and line up with my AX15 output shaft and the 6 bolt holes will also line right up
it is also long enough to engage the trans seal with plenty to spare so i feel it would not leak
BUT they stop about 5/8 of an inch from mating together completely

after examining the 42RE and the AX15 trannys
I can see that the seals are the same depth into the housings (give or take 1/8") and the shafts both stuck out approx' 1/2"

the difference lie's in the fact that the end of the 42RE output shaft is machined to a bearing style surface to ride inside that "collar" previously mentioned

that is the reason for the t-case input gear "collar" setup, it is apparently used to help keep the shafts running straight and true on at least the 42RE in some years

So the options are:
-machine down the end of the AX15 output to match the 42RE output's bearing surface
-cut approx 3/4" off the AX15 output shaft
-get a T-case for an AX15 tranny (i have heard there was an output shaft length change during the years, don't know for sure yet though)
-or as the guy above did, machine out the collar

using a 3/4 spacer will NOT work as an on road solution because you will pull the input gear out of the transmission seal and it will leak fluid through the weep hole

hope this helps somebody

rccolacc
09-26-2005, 08:13 PM
By machining out that collar in the input shaft, do you think I weakened it in any way? I figured since the '97 input didn't have a collar it was OK to cut out the one out of the '94. So far the Jeep is driving fine. No leaks or anything that I can tell. Hopefully it will stay that way.
-RC

DJJordache
11-05-2005, 02:36 PM
ok sorry about kinda bringing this post back from the dead but I was wanting to know if you have had any problems since you have run the machined input shaft for a while now?
I'm also going to swap a 249 for a 231 or maybe a 242

rccolacc
11-05-2005, 10:26 PM
No problems with the input shaft so far. I've only been off-road once or twice since the swap though. I have driven the Jeep probably 5K miles since then. So far everything's good. I love that 231 way better than the 249.
Let me know if you need anything.
-RC