Putting a TJ NP231 J Transfer Case into a YJ.......... - Jeep Wrangler Forum
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Old 03-29-2011, 08:00 PM   #1
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Putting a TJ NP231 J Transfer Case into a YJ..........

I have done alot of reading about the NP 231 J Transfer Cases in the TJ and YJ's. I wondered if I could put one in a YJ from a TJ after picking one up at a pretty good deal. The TJ case had already been rebuilt so I knew I could get rid of it if it were a no go in my YJ. I knew there were some differences but would they be enough to stop the show. I just want to lay all the wondering to rest. The Case went in great.

I first pulled my Case and set on the work bench beside the TJ Case for comparsion. I saw right away the only physical appearance was the tail piece on the TJ and output shaft was longer. The speedo sensor is electric in the TJ and the Vacuum sensor is different also. (No Biggie) The front yoke is different but not a problem. Both Casings even had the same casting numbers.

I removed the speedo sensors, the vacuum sensors, and the yokes from each and swapped around. The TJ was then ready for installation. I slid it right in and hooked everything up, except the rear drive shaft. I will need to cut mine or find a shorter shaft. (Didn't care about the SYE $$$)

I then started the Jeep up and tested all was good. Went into 4X4 perfectly. The light in the dash showed it was in 4x4. The speedo worked great.

I hope this helps somebody out when making plans for a Transfer Case change. If you want True Neutral and an output shaft that is sealed without rear drive shaft, this is the Case for you.

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Old 03-29-2011, 10:03 PM   #2
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i had to replace mine when i snapes the rear out lea shaft taking with it the housing around it. I had found a guy up in washington that sold rebuilt np231 with the sye kit and a new rear drive shaft for $750 didnt have th change any thing on it it when in and evry thing worked.

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Old 07-14-2011, 12:58 AM   #3
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question

i just got my tj tcase and i have a yj... now i put it in changed everything but the vacume because mine was broken... i started the jeep and nothing... i could put it in gear but nothing happened... is this because of the vacume? and how would i fix this
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Old 07-14-2011, 01:12 AM   #4
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Originally Posted by 95saharaGRN View Post
i just got my tj tcase and i have a yj... now i put it in changed everything but the vacume because mine was broken... i started the jeep and nothing... i could put it in gear but nothing happened... is this because of the vacume? and how would i fix this
I had the same problem. My input shaft is a 21 spline and the NP 231 I got had a 23 spline. It installed no probs but then the wheels didn't turn!

I had to rip it apart and swap the input shafts...Good news, it's not a tough as it sounds.
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Old 07-14-2011, 03:37 PM   #5
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Yea I got ahold of the guy who sold it and he will switch me this tj for a yj... So less work I'm good with that... I got under there yesterday and not only did I have to work on the tcase I had to do ujoints... Nothing major tho...
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Old 07-14-2011, 07:21 PM   #6
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you need to match up your input shafts there are like 40 different version for the NP231 family
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Old 07-15-2011, 07:55 AM   #7
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does the tj case have a fixed rear yoke or a slip yoke?
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Old 07-15-2011, 08:09 AM   #8
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does the tj case have a fixed rear yoke or a slip yoke?

TJ Has the slip, so a SYE is needed with a taller lift.... however the good news with the TJ 231 is you can run with out a rear shaft and not have fluid starting coming out like on the YJ version.
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Old 07-16-2011, 10:46 AM   #9
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ok i was wondering the point of changing to a tj case if its still slip yoke. doesnt seem worth it to me unless your having to replace it anyways.

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