4wd Problem/Noise

Hello, I have a 2000 2dr jimmy with 3 button 4wd.

The other day I was driving in Michigan and because it had snowed the roads were a bit slick so I decided to engage 4hi. When I did that I felt and heard a clunk under my feet; from what I could tell 4wd had engaged, but I had never heard that before when I engaged 4wd. I tried it a couple more times and it didn't always make that clunking sound, but now it does it every time unless I'm at a complete stop. Again, I feel it and heard it under my feet. I know it shouldn't be used on pavement, but this was in the snow in slick conditions, and any other time I tested it on the pavement to make sure it worked there was no clunking sound or feeling.

There are no lights flashing, and no lights have shown up on the dash, so the system seems to think it's working perfectly well.

It goes into 4lo, and it clunks normally into and out of 4lo just fine (the clunk I heard going into 4hi sounds different).

Any ideas or things I should look for?

Best to stop or be under 3 mph before engaging 4 wheel drive.

If you have it up in the air look u joints and drive shafts and axel shafts and engine and transmission mounts over and check transfer case fluid level.
Depending on what transfer case and mileage the fluid may may need changed and the newer transfer cases use the new GM blue fluid.
That needs serviced ever so many miles.

I'll take a look at the things you mentioned. The vehicle is above 90,000 miles, and I bought it used at 83,000 so it is likely that transfer case fluid has not been changed. How would I know what transfer case I have, or should I just check the fluid to see what color it is?

I always assumed you could engage 4hi up to 55mph, as per the manual, but I never do it at those speeds, usually around 15-20 mph.

Thanks for the thoughts.

We need the transfer case no off the back of transfer case for any more information.
233 or 236?
MT

I'll check tonight and get back with you tomorrow on whether it is 233 or 236.

It's a 233. I got under there and was kind of checking things out and I gripped the drive shaft at the end that connects to the transfer case and noticed that it was kind of loose. How much tolerance do these things have or should they be loose at all?

Could this looseness cause something to bind up and make it a bad idea to use 4wd until I can fix it?

I didn't check the fluid yet, any idea what size hex wrench I'll need to loosen up that bolt?

If you are not sure about it.
Be best to have a good repair shop look at it.
Good Luck
MT