4405 failure, what would cause this?

[Bhain]

I recently had a transfer case failure in my 99 explorer. It has the part time 4405 TC. The problem was that it had completely locked up in 4WD. While it would shift from Hi to Lo (and back) and would also show indicator lights as in 4x4 mode and out, it was locked up solid. I ended up getting a used transfer case from a wreaking yard and am in the process of swapping it out. At the moment I am waiting on some parts to be shipped and got bored so I took apart the old transfer case to see what might have caused the failure. I figured I could not make it worse, might as well learn something. Drained the fluid and it was old, but not burnt. No visible metal bits. Split the case and did not see any broken parts, bits of nylon, nothing. Magnet was pretty clean, a little shavings, but with 179k miles, I would expect to see some trash. The range fork looked fine, nylon inserts were not warn at all, none of the usual issues at all. It wasn't until I took out the clutch drum that I found the problem. All, and I mean all, of the friction material on the clutch plates had separated from the plates and was crushed inside the drum. The pieces were to big to find their way out of the drum so it just locked up. The plates themselves were not discolored (heat) nor were the pieces of friction material. It was as if something was introduced to the oil that caused whatever was used to adhere the friction material to the plates to simply fail. Aside from this, nothing else seems to be wrong with it. Anyone ever see this before? What might cause this kind of failure?

 

[JK080]

Hard to tell from your picture but if the clutch material has come off the plates that's a good indication of water contamination at one time.

 

[Bhain]

Hard to tell from your picture but if the clutch material has come off the plates that's a good indication of water contamination at one time.

That is odd, we have owned it since 2000 and it has never been in a flood. There were no signs of water in the fluid that came out of it. Also the breather hose was intact and in place. No doubt it failed for some reason. Would a pump failure cause this?