difference in 231s

whats the difference between the pre 1996 np231s and 97 and up np231s? is it the tail shaft housing? if so could I take new tail shaft housing and put it on the case? or is the speedo sensor totally different?

Both the tailcone and the output shaft are different.
Go here and scroll to the bottom for pics of all the output shafts.
http://4xshaft.com/SYE_detail.html

well I have another output shaft from a newer also. I was wondering this because I found some cheap SYEs but they are for newer 231s

The new ones are cheaper because there is no need for a seal that will keep the fluid inside the case. SYEs for older ones need to include an oil seal.

right. i guess what im asking is can I swap the output shaft and tailhousing onto the back of the case would i have any issues.

Depends on the actual year,other variables are spline count/spline length.The late model cases also deleted the needle bearing cages,it can still be done but you might need addditional parts.

i learned this one the hard way. my tcase on my 89 xj went out- i bought a used one from a 91-ish grand cherokee, both 231's, swapped the cases and jeep wouldnt move. i had to drop the case again and split both of them and swap out parts. the input shaft was a different spline count. i was able to swap my stuff, best bet is to split both and look. also, my speedo sensor on the cases were different. do it all in one sitting so you remember how to put it all back together