Np231 Diameter issue?

Hi guys and thanks for this great forum!

I'm replacing yet another t case on my 93 XJ. This time i'm too busy and lazy to do it myself. "although that's probably whats going to be done after all." The Mechanic is telling me the new t case i provided for him won't fit due to input diameter size. It is a 23 spline out of a 91 xj and my xj is a 93 automatic.. 23 spline as i have replaced before. My question is can anyone confirm that np 231's have diameter issue's when switching from one year to another? I have never heard of this issue and have searched this thread as well as google with no luck. I keep reading that they should be interchangeable as long as the spline count is correct. Any help on this would be greatly appreciated.

Thanks

External case is the same, always. In 1991 the switch from 21 spline to 23 spline was complete (it started with the 23 spline output in the AX-15, mid-year 1989). Is he trying to graft the two cases together? If so the planatary gears did change in the mid-90s; I'm not sure if anybody has ever bothered to nail down exactly when (or if it even had a firm date). You can even drop an early planatary 23 spline input gear into a 21 spline case if you want.

Sounds like your need a new mechanic

Actually I should be more specific. Hopefully i'm describing this correctly. It's the input shaft? The actual part on the t case with the 23 splines. He is saying won't connect to the tranny due to being different diameters. I didn't realize they used different diameters on the np231 thought i was golden if I got the spline count correct. Anyways there isn't two t cases. It's just a 23 spline 91 to fit into my transmission. Apparantly they are not lining up correctly. Meaning the Tranny and T case. Due to a diameter issue? Not the external diameter but the internal part where the male part of the tranny meets up with the female part of the t case. The spline count is correct on both the t case and tranny.

They didn't use different diameters. The splines are wrong, or something is rusty and won't slide in, or he's just failing..

There is a difference in *length* though. The AW4 uses a 'short' input 231, while there are some 'long' input 231's from ax15s..

Thanks for the help on this one guys. You saved me a lot of time and grief.

Figure out what it was?

Working on that now. Looks like it's mostly dealing with a mechanic that doesn't know anything about 4x4. I went with a friends suggestion on picking this mechanic. Not the best decision i've made. I'll give an update when I figure it out for sure.

It's coming home today .. VIA tow truck. LOL .. This guy is an idiot. I'm just going to do it myself. He's fighting me on the 500 bucks he says i owe him. Told him i would split the difference and we go our separate ways. This has cost me too much money. Lesson in hard knocks. Don't trust the majority of mechanics out there. Just save you the grief and do it yourself.

Time for an Atlas.

Nah, just find someone selling a 241J cheap, and BFH the crap out of the trans tunnel :gee: And the linkage, and the crossmember.....

David Bricker / SYR

did the donor case come from an auto or a manual? What part number is stamped on the round tag on the back?

For a 91:
5300 8209: 4.0 six cyl, XJ MJ, five speed AX15 or auto trans
5209 7522: 4.0 six cyl, XJ MJ, five speed AX15 or auto trans (23 spline)
5209 7526: 4.0 six cyl, ZJ, four speed auto A500SE electric shift, 93 (this one may be a problem going into an XJ, I forget)
5209 7534: 4.0 six cyl, ZJ, four speed auto AW4, 93, 4.0 six cyl, ZJ, all manual trans, 93

There are others listed but they apply only to China/KDX export edition vehicles and I'm almost certain you wouldn't have one of those cases.

Since you already verified it is a 23 spline and it came out of an XJ it should just fit. I bet he didn't put it in gear and wobble the output shafts while mating it to the transmission so it happened to hit spline to spline instead of sliding together. Wouldn't trust that mechanic again that's for sure.

edit: the 7526 case is indeed a problem, it's got a specific input gear that will only mate with that transmission AFAIK. I'm 99% sure I have one of those cases torn apart at the side of a friends shop, I got all the way through an SYE install before discovering it bottoms out 1/4" from seating fully on an AX15 or AW4.

Also, the input gear tooth profile change is 94.0 to 94.5 - you can swap input gears as long as you stay on the same side of that split, i.e. worst case you could put your 93 input gear in the 91 case and reassemble it.

I think you nailed it Kastein. I started putting it all back together today. I got further than the mechanic at least. Although i'm about 1/4" off. Looks like I have the longer input shaft model. YAY>. Time to find a new input gear and swap out. I no longer have the original. If anyone knows where i can pick up one please don't hesitate to tell me. It's the longer input 23 spline shaft i'm looking for. Thanks for all the replies and help!

Peek down the input shaft inside the splines. If you can see a bushing that is the approx same diameter as the inside of the spline instead of the outside, you have the case that's going to not fit at all. There's a chance you can disassemble it, punch the bushing out, and reassemble it but I haven't tried this yet.

What's the 8 digit chrysler part number (probably starts with 56) on the red/silver round NVG/NP tag on the back of the case you have now? I can see what exactly it claims to fit, which should make it easier to find the proper input gear to swap in, worst case you can buy one from the dealer or Novak.

If the input is simply too long and bottoming out before the tcase seats against the transmission, is there any reason he can't just cut the input down a bit?

It is possible to cut the length of the input shaft, just gotta take your time and make a square cut. I think there is a write up in Stu Olsen's site...think he did the same thing when swapping a manual tranny for an auto. The input on the transfer case he was using was the long style input and he cut it to fit.

You can... not sure I would. Especially in the case of the funky ZJ transfer case with the bushing, then you can cut the input gear all you want, it still won't seat any deeper

That was NOT a fun evening when I got bit by that problem.

Sorry for the late response. I have two housings i can chose to play with if need be. Both are np231j assembly #53008208. The serial number on case A. is 53902 and case B. is 45902. I haven't had a chance to look down the input yet. Will check first light.

David_Bricker said:

Nah, just find someone selling a 241J cheap, and BFH the crap out of the trans tunnel :gee: And the linkage, and the crossmember.....

David Bricker / SYR

Click to expand...

i must have gotten lucky, mine fit like a glove. i have a manual trans though, so it may be a little different.

kastein said:

Peek down the input shaft inside the splines. If you can see a bushing that is the approx same diameter as the inside of the spline instead of the outside, you have the case that's going to not fit at all. There's a chance you can disassemble it, punch the bushing out, and reassemble it but I haven't tried this yet.

Click to expand...

Had this problem putting a 242 in my 5.9 ZJ.

Yes that bushing comes out. Just press out the roller bearing in the input gear, the bushing falls out, and put the bearing back in again. Input shaft length wasn't a problem.

Just sucks that you basically have to take the whole case apart to get to it.

Thanks for all the help guys. After a few hangups with switching to the longer shaft I got it all installed.