Loud thunk when disengaging 4wd stopped?

Hello, I'm new to the forum and new to Jeep's so I'm trying to get familiar with my 99 XJ that I've had for about a month. When disengaging 4wd high there used to be a loud "thunk", which I thought was the front diff disconnecting.....however, I actually have a non-disco Dana 30. The noise went away after I buried the front end in a snow bank and rocked it free again. I haven't lubed anything yet and I don't think the previous owner used the 4wd................ so does it just need lubed somewhere?

99 xj
4.0 I6
manual ax-15 tranny
Dana 30, non-disco
Chrys 8.25
NP 231

The T-case should disengage with no unusual noises. Seldom used T-cases can be difficult to shift or slow to disengage. On rare occasions, the T-case and drive line can become bound up and will disengage with a clunk.

You should drain and re-fill the T-case with Dexron-III/Mercon transmission fluid and see if that helps smooth out the shifting. Make sure the fill plug can be removed before you drain the T-case.

It could also be linkage adjustment; the shifter can feel OK, but you may not get full engagement or disengagement sometimes even with low usage. There are a lot of threads covering this - hit up the search for more info.

Thanks, for the replies. I plan on changing all the fluids soon and I'll dig a little deeper for similiar threads.

It should not make a thunk, but often will if your tires are poorly matched. If you're sure it's engaging and disengaging, but has stopped thunking, you're good. Did you, perhaps, check your tire pressure recently? Sometimes that's enough to make the difference.

You can check it all pretty easily, if you can get somewhere like a dirt road. Put it in 4 high, goose it, and if it kicks gravel at both ends, you're engaged. Take it out of 4 high, goose it again, and if it kicks gravel only at the rear, you're disengaged.

It's definitely engaging and disengaging fine now.......I did the figure 8 routine to make sure. I also stuck the rear axle on some ice in 2wd and made sure the front axle wasn't turning. It does have a mix of tires.....the front has GY Wrangler truck tread and the rear tires have a basic car tread. A 2" lift and BFG 30's are in the plan to fix that.

Tires can be a "B". Same size tires from different manufacturers can vary in size quite a bit, the discrepancies are bigger on the larger sizes but still show up on the smaller sizes.

Keep matching sized tires on a single axle with equal inflation pressure.

If you have a doughnut "space saver" spare don't use 4wd with it mounted.