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NP 231 input shaft


NAXJA Forum User
Alright I am going to try to explain my whole situation the best i can and not leave out details, bare with me.. i HAD a 2001 4.0 xj 5 speed (nv3550) with a 231 t case. currently have a motor from 1999 which i swapped parts to run in my 2001 and my t case is from a un known year xj with a ax15. so my current set up is 1999 motor with a 2001 nv3550 trans, and a t case from a ax15.

when i let off my clutch, not even all the way i get a very bad shaking. i still havent not let the clutch out all the way. i thought it was my u joints in the rear so i replaced them, still have shaking. i thought maybe the master and slave cylinder for the clutch have air in the line so i bled it and got all air out, still shakes.

When i replaced the clutch when i did the motor swap i made sure the pilot bearing was seated all the way, fly wheel was new with new clutch kit. no oil or any foreign bits were on it. cover plate on bell housing was installed also.

the next thing i have been looking at but want more opinions on is the t case from the ax15.. i have read that the 231 has different input shafts depending what tranny was mated with it from the factory. i removed the t case to see the splines but did not see any chewed up/ broken teeth. both are 23 splined. i have also read that the nv3550 has a short output shaft making the t case having a long input shaft. i look at my current t case input shaft and it only sticks out of the t case not even an inch. 7/8 in about. would me getting a longer input shaft do anything?

Just trying things, i got the rear end off the ground on stands started the jeep, put in first gear and no shaking.. no load on the motor or trans so the trans and t case may be touching but not fully married together. but wouldnt i see and hear the splines eating each other?

i hope i explained it well enough for you to follow.

if anyone is wondering what happened to my old t case... it was scraped when i was traveling for work on accident by my roommate. he claims he did not noticed it was freshly rebuilt. (it was all clean and pretty, had a sye kit in it and looked brand new, away from the scrap pile in the garage but somehow he thought it was scrape..

thanks in advance for the help.
Just an update.. since no one had anything. For future problems for someone. Yes the input shaft on the transfer case was too short once I put in the new one from cobra transmission it worked as it should.

One thing I had to do was get a pilot bearing for the output shaft that goes in the inside of the input shaft. (Put it all together and was binding so I took it apart to find that the new one didn’t come with a bearing)

Simple install just have to be careful.
There might be a tag on your transfer case identifying the year it was made.
That wouldn't be of any help as there was different ones within the same year for different transmissions!