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.