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I want an auto

Jerm S.

NAXJA Forum User
Northern Utah
I have a donor 88' Xj that has an aw4 auto trans and all the trimmings to go with it. My xj is an 88' also but it is a 5sp with that bad ba10 trans. I want to take the trans out of the auto and put it in the good XJ. Heres the catch my working xj is lifted close to 7" and has an sye in its 231 tacse. I have heard that there is some problems when you want to go to an auto, with a 231, that was mated to a 5spd. Something about the input shaft on the 231 is longeer for the 5sp than the auto and they may be different splines. can any one confirm this for me and tell me if the input shaft from a 242 wil fit in a 231.

Here are some adtional specs if you need them.

Donor jeep is an 88' 4.0 AW4 auto trans and 242 tcase. it is lifted 3"

Working XJ is an 88' 4.0 BA10 5spd trans sye 231. Lifted 7"
Since they are both 88's,you should be able to switch out the input gear if needed!
No the input shafts wont tansfer over ad according to AA adapter manual the shaft for the 5 speed in some aplications is 1/2" longer than the one for the AW4....
That's a question that would be good to get a definitive answer to. I had never heard that, and assumed that the 21 spline t-case from a Peugeot and the 21 spline case from a pre-'91 AW4 would interchange.

I would have answered this question by saying....yes, they will interchange, but the real issue is the wiring harness to hook up the TCU and trans.

Anyone know for sure? Maybe a trip to the Jeep store to look through the parts book is in order.
The input gears can be switched, take out the planatery gears, and the input gears come out (IIRC)


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This swap will require you to change the input gear on your transfer case. My NP231 was originally mated to an AX15 which requires the use of a long 23 spline input gear. (I believe that a TJ with the 3 speed auto also uses the long version.) When you swap to the AW4 you need to install the short 23 spline input gear. There is about a half an inch of difference between the two.
Hey Jerm, you know, XJEEPER swapped an auto into his '89 a couple years back. He could tell you what you'd need.
Alright Jerm, let's work through this together. I just found an 1988 21 spline AW4 to replace my Peugot. I have a 21 spline count 231 with a Tera 4to1 installed. When I ordered it from Tera they did not ask me if I had an auto or 5spd...just the spline count. So with that said...shouldn't my 21 spline 231 fit my new AW4 21 spline? Tera didn't care what I was attaching it to...just that it was 21 spline.

To help you...The 4to1 kit that comes from Tera is, I believe, basicly the front of a 242 case and a new planetary. So...a 21 spline 242 should fit a AW4 21 spline. That doesn't say that anyone else is incorrect, there may be a difference in the back of the 231 case that causes it to not match up with a regular AW4 21 spline.

I feel like I just played 7 degrees of Kevin Bacon...

Anyone, please help us with this misguided logic. :)
I beleive its only the 23 spline that has two different lengths.I went through this when I did my Tera-Low kit!
Yeah, it must be just the 23 spline. I also have a 4 to 1 that's 21 spline ('88). It was first in a 4 cyl TJ, (21 spline), and it went right into my 21 spline XJ with an AW4. Later on, one of the pinion gears came out of the planetary when a pinion shaft came out/broke. Tera never asked me anything when they sent me a new 21 spline planetary.

BTW, if anyone has their Tera 4 to 1 out for any reason, consider puting a spot weld on the pinion shafts in the planetary gearcase, where they are only staked in.
That's only on the older Tera unit's right Ricardo? The new ones come welded?