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Discussion Starter · #1 ·
Have a quick question for the experienced jeepers here.. I have an 88 YJ automatic with a NP 231 t case that's starting to make some noise. I found a tcase from a friend of a friend he "said" came out of a YJ.. I went today and bought it for 50 bucks. The tag was all covered in grim and dirt I scratch the surface enough with my finger nail to see it said 231 on it. Upon closer inspection at home it say 231HD on it. I was wondering if this is still a direct swap and if it was a better/worse tcase that what I have? Any help would be appreciated!
 

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Discussion Starter · #2 ·
additional info.. I cleaned tag alittle better and it actually says 231D-HD.. if that makes a difference?
 

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I just googled it. Looks like the 231D comes from a Dodge. The letter at the end indicates what vehicle it came from. So D-Dodge, C-Chevy, J-Jeep. It looks like you can do some modifying to get it to fit, like input and output shafts, but I don't know the specifics.
 

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I did a little looking too, and as YJ fanatic said, it's from a Dodge. I got the impression you can use the Dodge back half with the Jeep front half to make a 231J-HD, much like people do with a 231C on a Chevy swap. Didn't find any specific info on that, though.
 

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It might be if it was already set up, but impossible for me to say without seeing it. Can you post some pis of the t-case?
 

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That case will be a 23 spline input and your auto will have a 21 spline output. You can't swap the input shafts since the annulus gear and planetary gear have different gear cuts. 88-93 have flat cut gears and 95-06 have sharp cut gears.

Here's a picture that shows the difference, the older gear cut is the top and the newer is the bottom




The 231D-HD is the dodge case with the wider chain, so you could swap that into another case, here's a picture to show the 231D-HD chain next to the regular 231 chain. Also, jeep and dodge have the same bolt pattern on the np231, the big difference is the input gears are usually different. If you have the right spline/length input gear installed on a dodge case, it is direct bolt on.


 

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Discussion Starter · #9 ·
Thanks for the replies.. I took a good look at it today and the tail piece is different(longer) it don't have a speedometer sensor.. I couldn't make any comparison of any of the shafts cause the tcase is still in my jeep. I though I read somewhere you could take the two and make one tcase that would work. Im pretty mechanically inclined but just don't have much experience with these tcases. Guess I just wasted 50 bucks.. Ill try to sell it to recoup my money and continue the search for a 231j.. coulda been a worse mistake I guess..live and learn I recon.. I really do appreciate yalls help.. Mines not really out yet.. its just making some bearing noise that's driving me crazy. Ive changed fluid with ATF+4..no change.. I read some guys use 5w30.tried that for a day.. no change in the noise.. drained that back out and replaced with ATF again.. I shook both driveshafts..didn't seem to have much play... but there is def a noise. Me and my sons jacked up all four tires and run is and really couldn't hear anything.. but when driving the noise seems to be right under my feet.. which is why I drives me so batty I guess.. thanks again men..
 
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