Hey, new here and proud owner of a 97 XJ!!
But noticed some pooping noise when in 4x, found out my chain in t-case was amazingly loose.
So Im "rebuilding" the case. I got a donor case, and the insides are really good.
BUT
some things are different.
I think its the mode shift synchronizer gear. Mine has slots in it, and the donor in better shape is solid. Whats better? Why different?

Also In all the part diagrams for the NP231, it shows a output housing extension, but mine has a small housing. So took forever to get the right output seal. Why is mine different?

Sorry Newbie here!!!
Here are pictures to kinda show the gear. First mine, second the donor part

 

There are slight variations to the 231. I would say don't switch anything and just throw the other 231 in as it is.

 

Hello!

I also have a question - The NP 231 that the XJ uses has a 1" chain correct? I am told the 1 3/8" chain is in dodge applications. Going to order a rebuild kit and want to swap in a new chain also.

Do you run these until they fall apart or proactively tear-em down?

Thanks.