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Unread 02-16-2009, 12:32 PM   #1
pflugs
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NP231 TCase won't mate to 6-cyl Tranny

I am performing an engine swap on my 1993 YJ Wrangler. I am trading a stock 4 cyl for a 6 cyl with about 72K miles. I also bought a tranny from a salvage yard that came out of a stock 93 YJ that had front end damage.

I've successfully mated the new AMC 242 6 cyl with the tranny (admittedly, not 100% sure it's the AX-15 I only get to work on the vehicle on Tuesdays, so tomorrow I will try to determine the tranny model number). I then tried to install the transfer case from my original 93 vehicle, and the splines didn't match. The transfer case has a label that says "NP 231 J". My original research told me that I could use this combination, but now I'm stuck.

In Googling the forum here, I found some people referring to a "21 spline shaft" and a "23 spline shaft". Can someone provide more info here? Can I replace the T-case input shaft with a different one? Not sure where to begin....

Thanks in advance for your help,
Pflugs

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Unread 02-16-2009, 01:09 PM   #2
flys_yj
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your google serch is correct, the ax-5 has a 21 spline output and the ax15 has a 23. it is possible to replace the input on the 231.
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Unread 02-16-2009, 01:44 PM   #3
Leans93
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I recently did a similar swap. As stated you must swap out your 21 spline input shaft for a 23 spline. You have to take your t case apart to get to it. I'd set aside a few hours for the job. I got mine for about $125 dollars.

This is the piece that will be swapped
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Unread 02-16-2009, 01:47 PM   #4
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Sorry seems to have posted twice
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Unread 02-16-2009, 04:51 PM   #5
themonkeyman
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Quote:
Originally Posted by Leans93 View Post
I recently did a similar swap. As stated you must swap out your 21 spline input shaft for a 23 spline. You have to take your t case apart to get to it. I'd set aside a few hours for the job. I got mine for about $125 dollars.
This is the piece that will be swapped
For that much you might wanna just look for a new T-case. It will probably run you about the same amount of money but save time for you. Plus, you can then sell your original case and recoup some fund-age.
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Unread 02-23-2009, 02:11 PM   #6
pflugs
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Thank you for the input! Would you be able to tell me where you got that replacement part?

Thanks,
Pflugs
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Unread 02-23-2009, 04:28 PM   #7
dmock
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See if there is a transmission supply company near you. I just bought the 23 spline piece for 56.00 from a company called TPS here in Texas. They had to order it in (next day), but I saved a huge chunk of cash! They also had the gasket set for the NP231 for less than I could find it online.
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Unread 02-23-2009, 04:38 PM   #8
TheRealOldjeep
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Easiest to just get the right case. There are more than just 21 spline and 23 spline as variations, there are also length differences.

I think this marks the 400th time I've posted this link on a forum
http://novak-adapt.com/knowledge/np_nvg_input_gears.htm
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Unread 02-23-2009, 04:52 PM   #9
Leans93
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Well in my case I knew that my transfer case was in good condition. Also I prefer doing all the work myself. It's part of the hobby for me. I had no interest in searching for another transfer case with the correct gear that may or may not be in good shape. I got the gear at a local salvage yard that deals in new and used Jeep parts. the gear was fairly easy to change out IMO. While you have the case open you can change out seals if they need it. Each to their own I guess.

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93' YJ 4.0L AX-15, 4" Pro Comp lift, 3/4" shackles, 1" BL, 33x12.5x15 BGF MT's, and some other stuff


Quote:
Originally Posted by Mike Jones
Catch me on the highway or about to tear the mall up.
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Unread 02-23-2009, 05:03 PM   #10
TheRealOldjeep
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I've changed them out, but I've also got 6 or 7 transfercases sitting around and understand the differences. Problem is that people keep saying you just swap a 21 for a 23 without understanding that there are more options than that.
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