grinding noise when i put it in 4wd!

hello all! thanks a lot in advnace for any insight.
i have a question. my 1998 GC has a slight "jingling" rubbing noise coming from the differential(i think) but its 100% driveable and drives smoothly
i went as far as to jack the car up take the front passenger side wheel off and spin the wheel by hand and i heard "it" on the other side of the car at the differential(this my first 4WD vehicle,im not exactly sure what the proper name is for it) where the drive shaft connects from the trans
but when i put the stick in 4WD it makes an awful cracking grinding noise and jerks. needless to say i can drive it in 4WD at all.
if it was my differential would i still be able to drive it in just regular 2WD for awhile? or will it just go completely? i been driving it like this for a week now.
i have not checked or replaced any fluids in the differential or anything like that and im not sure if the previuos owner had done so (i bought it used)
if filling the fluid is the problem is it too late now? any knowledge would be greatly appreciated......

Sounds like you need a new transfercase if it's making those noises.

Well changing the fluids wouldn't hurt. It might help but if they have been driven with degraded or old or no fluid for that matter it may be too late. Maybe not though it's worth a try. Look for any metal debris in the fluid when you change them. And make sure you use the correct fluid. From your description though it sound more serious though. Good luck and let us know what happens.
ByronP

thanks everyone for thier help and giving me some valuable info.
anyways,the damn trasfer case was TOTALLY EMPTY!! unbelievable. i opend the drain plug and NOTHING came out
i never noticed any trans fluid spots anywhere in the driveway.but on second thought, i have a '71 pontiac grand ville i restored and it has a very,very slight oil leak,maybe i just wrote it off as being my car and not the jeep.(wish i havent done that in retrospect) i filled the case up and the noise went away but i think the 4WD is cooked! still grinds and pops when i shift it in
well,at least i can still drive it. i fee like an idiot,i should know better than that crap. how much do you think getting a new gasket on the transfer case would be? thanks..........

Just ask them to include a new gasket with the new transfer case (bad j/k I know)

Which transfer case is it that you have??

Some one on here had a 249 that was pumping tc oil into the transmission.

not ususal but could be your problem too.

JD

haha,yeah,bad joke for sure!!
damn, those things are quite expensive! but nothing inexpensive or easy ever goes out though,you know how it is.
seems mine is a 242 J as the tag reads. im surfing the web for 1 and i keep finding different year matches. one says the 242 J is for GC years 87-90 and one says 1999-01(sounds more likely to me)
looks like a rebuilt one will run a good $900 plus shipping. im going to search the trusty junk yard for one here. hopefully i do better than $900! is it incredibly painful to install/take out one? or is it better to just purchase the rebuild kit? id rather go the EASIEST route...............

if you can find a used one with low miles on it from someone you trust - go for it. They should give you a 30 day warrenty with a used one for sure.

Otherwise I'd go for the rebuilt one with a warrenty.

The assembled unit is the easiest as it is just R&R and your are on the road again. IMHO anyway.
The rebuild kit is for someone with tools. experience and a good manual not to say that a person couldn't do it but......

The TC is awkward to manage without a transmission jack and it weighs a lot to manhandle under the vehicle

JD

it probably just stretched the chain.thats not that difficult to replace.but if its really stretched it could grind a hole in the case