21 spline input in newer transfer case?

Hey I'm wanting to swap to a np242 in my 87 4.0 AW4 np231 xj. I recently learned about the retarded spline count difference and was wondering the compatibility of the 21 spline input in the 96+ tcases. I heard it can be done 95- but 96+ has a different number of planetarys but if that is the case and the input isn't compatible can the planetary case be swapped along? This is a light wheeling rig that I'm currently swapping an 8.8 cause of the d35 taking a dump. All the jeeps at my local junkyard are 96+ (clunkers) and was planning on a tcase from there. I like the idea of AWD for the rain and ice and many people seem to like theirs.

You can get a newer AW4/np242, and swap both in. WOuld probably be the best/cheaper route.

X2... anything up to a 95 will bolt right in (if you also swap the transmission.) Anything up to a 96 will bolt right in but require that you swap the rear driveshaft as well. Anything up to a 97 will bolt right in, but you will have to swap the rear driveshaft and splice a few wires. 98 and up will require sensor swapping, splicing wires, and swapping the rear driveshaft.

I'm trying not to swap the tranny cause the one in mine is pretty fresh and i don't want to spend the money on a tranny either (how is that the cheaper route?) Also all the jeeps at the yard are blown cause of dumb ass cash for clunkers bullshit so I believe you wouldn't be able to rotate the torque converter to unbolt it (correct me if I'm wrong) and last they also destroy the transmissions when they XXXX everything up anyway. Sorry for the language but I think C4C is the dumbest idea in the world and their alls their doing is wasting more materials and energy than it would be to drive the same 5 year old car getting maybe 2 mpg worse. Thats what you say to hybrid drivers who say your polluting the enviroment. "I'm reusing and recycling while your car is using up current natural resources to be manufactured motherXXXXer"

Well, if you find a functioning trans/t-case combo.. especially for decent price, you dont have to tear down/or have someone tear down the 2wd trans and swap tail cone/ output shaft. So yes, cheaper.

I'm not talkin about swapping the tranny output or anything dealt with the tranny. I'm talkin about swapping only transfer case components in order to mate to my 21 spline aw4 which is currently mated to a 21 spline np231 not 2wd.

anything up to a 95 will bolt right in (if you also swap the transmission.)

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Actually (not from own experience) 23 spline t cases from 95- you can swap the input shafts themselves with the 21. This seemed like the best route just if I can find one. (I can't go to most of the major junkyards where i live cause they got 18 or older rules which is messed up, ill be 18 in like 3 months but winters coming before lol)

Super mud said:

I'm trying not to swap the tranny cause the one in mine is pretty fresh and i don't want to spend the money on a tranny either (how is that the cheaper route?) Also all the jeeps at the yard are blown cause of dumb ass cash for clunkers bullshit so I believe you wouldn't be able to rotate the torque converter to unbolt it (correct me if I'm wrong) and last they also destroy the transmissions when they XXXX everything up anyway. Sorry for the language but I think C4C is the dumbest idea in the world and their alls their doing is wasting more materials and energy than it would be to drive the same 5 year old car getting maybe 2 mpg worse. Thats what you say to hybrid drivers who say your polluting the enviroment. "I'm reusing and recycling while your car is using up current natural resources to be manufactured motherXXXXer"

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Oh believe me, you will find very few people who will disagree with this here.

You could get the tranny out without unbolting the torque converter, but yeah, I can understand wanting to keep yours.

you can actually swap the front half of the cases around, or just swap planetary gears and input shafts.. i did it when i swapped to an ax15, and it worked for a long time, until i filled the tcase with water and the bearings and gears got eaten up.

thechief86 said:

you can actually swap the front half of the cases around, or just swap planetary gears and input shafts.. i did it when i swapped to an ax15, and it worked for a long time, until i filled the tcase with water and the bearings and gears got eaten up.

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this, as long as your planetary/input bearing and front output are in good shape.

We fixed Redheeps 242 with a junkyard 242 in Tellico. Of course it had the wrong input gear. So we took the grand cherokee mainshaft and backhalf of the case and mated it to the good planetary and input shaft. Frankencase made it from Tellico to NC, and then wheeled Moab. Jus be aware that you may need to swap guts if the backhalf of the case will not take your speedo gear.

I am not sure if you can mate the front half of your 242 with the rear half of a 231. I would imagine that the cases are the same, but the mainshaft/guts may be different.

I'm pretty sure you can't mix 242 and 231 parts. I will try and remember to look it up later tonight.

kastein said:

I'm pretty sure you can't mix 242 and 231 parts. I will try and remember to look it up later tonight.

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My guess is that the planetary and input gear are probably the same, as tey have the same gear ratio. The mainshaft and such are most certainly different, and I imagine the case is different as well to accomodate the different mode forks

I would probably call novak and ask, as they make replacement input gears and can probably tell you if the inputs can be swapped, or if they're the same part.

At the very least they could probably sell you a 21 spline input gear for a 231. $50 for an input gear is still better than removing and replacing a working AW4.

ere's the site:
http://www.novak-adapt.com/knowledge/np_nvg_input_gears.htm

I went and looked, they list the 242 gear as interchanging wit hthe 231. I would go pick up a junkyard 242 and swap the input gear from your 231.

WARNING:

I don't recall the break point precisely, but I believe it was around 1994/1995 that NP changed the helix angle of the input gearset sligthly. You probably won't feel anything amiss while assembling, but you'll notice the problem once you change the fluid in the thing next time (when you see all the silver glitter.)

I do believe that the 21-sp input set uses the same helix angle as the early 23-sp input, but I have yet to be able to confirm this.

WARNING

Alright thanks for the good amount of information. What I've concluded so far is i can only swap inputs with tcases before 94 because of the change in the helical gear cut. I still haven't found much info on swapping the planetary and input but I also found there are 2 different bearing sizes used also.
So I think a pre94 242 would be the best bet considering the gear cut and possible bearing difference for a newer tcase even if the planetarys swapped.
Though while swapping the planetarys that would eliminate the gear cut difference (just realized) and if the bearing sizes are the same then it should work.
Also do the earlier 242s work as smooth as some of the newer ones for ex. being able to shift on the fly through pt4wd to ft4wd and back into 2wd?
I have to back up to get my 231 out of 4wd which is a pain on the road and didn't know if that was a developed problem or a common thing and could develop with an older 242.