While I have found a few threads that mention this problem or similar, I am having trouble finding one that matches exactly and/or offers a resolution. If I missed an obvious thread, feel free to flame me.

So the short version is, my '98 Disco has developed a clunk/thud/knock when going from acceleration to deceleration. I am fairly confident it has been narrowed down to the transfer case, but just in case I am missing something I have listed all the troubleshooting that has been done below.

- Noise seemed to start after fluids replaced (75w-140 if I remember right), lift installed (2") and bigger tires installed (all completed over the course of a week), although the timing could just be coincidental.
- Removed the front drive shaft and drove with just the rear. Sound was still there but seemed a little quieter.
- Removed the rear drive shaft and drove with just the front. Sound was still there and seemed a little louder.
- With the rear shaft off, rotated the rear shaft mounting bracket on the t-case by hand and it had some play (1/12 of a turn or so) back and forth, and seemed to make a clunk when rotating back and forth.
- With the front shaft off, rotated the front shaft mounting bracket on the t-case by hand and it had some play (1/8 of a turn or so) back and forth, and had an even more noticeable clunk sound.

So, with all that said, does it sound like my t-case is toast? Is it worth pulling the access panel off and inspecting the gears? Am I just over-reacting and the play and sound from the t-case is "normal"? Am I maybe just missing something else that I didn't think about? Any help would be greatly appreciated.

 

My t-case makes so many noises it's crazy, whines, clunks, clanks.. Some day it will blow up and I'll get a new one.

With that said it could also be diff bearings or a bad u joint

 

Theoretically didn't I rule out u-joints, drive shafts and the differentials by running it in both FWD and RWD (1 shaft removed and the CDL engaged) and still getting the same clunk?

 

Haha!! I love it! I'm right there with you. Eventually you get to a point where you just say "screw it" and you drive it till it breaks. Like the old rappers would say "throw it in the gutter, go buy another".

You didn't necessarily rule out the UJ's. Some clunk is expected.
When you dropped the front DS you said it was quieter. When you dropped the rear DS and put the full load on the front DS you said it was louder. Look to your front DS. Check the UJ's. If they've never been replaced, replace them. Or buy mine, I have a front DS with brand new UJ's installed. Then you'd have a spare.

 

Yea I'm waiting until I can find a good deal on a 1.4 geared case or until mine explodes which will probably be soon.

I have a GBR double cardan front shaft for sale $200 and $50 for shipping... rebuilt 10K ago

Put truck in neutral to slacken drive shafts while still attached. Try to push them up and down to see if the UJ has play. If all UJ's seem tight then check your transfer case mounts. If those seem solid then I'd say you have probably the average amount of clunk as the rest of us. Mine doesnt make an terrible audible noise (that I can hear over the MTR's) but I can feel the play when I let off the pedal especially on the highway..

Remember when you lift these things, put bigger heavy tires and start doing all sorts of crazy mods and **** they arent going to be the luxury vehicle they once were when they were stock.

I used to care a lot more about noises, steering wheel vibrations from unbalanced big beefy tires etc.. But I mean look at my truck - what should I expect

 

I guess I am paranoid that this noise might turn into something major. If you guys say some clunk is normal in these trucks (already tested the ujoints like you mentioned...and will inspect the mounts tonight) I will just turn the radio back on and call it good. Out of sight/sound, out of mind.

 

After reading all this, about the only thing I would add is that it is a big set of mechanical gears (which is good), you went to larger tires and a lift, so everything is under a larger load in a different relationship than what it was.

If you replace now, you are just doing it prematurely. However, grabbing a spare like Fish offered would be a good thing to do. Mine clunked a little when I first got it. Changing to a good 75-140 synthetic quieted mine down a whole lot.