I noticed the bi-metallic strip and came to the assumption it rotated an internal valve to close off or open up orifices to either lock up the torque converter more or let it freewheel.

I think maybe the problem might be more like there is a lack of fluid, like some of it has leaked out over time. I see no oil residue on the drive but the previous owner I think pressure washed things pretty often. One other poster suggested drilling a hole and replacing lost fluid and that would probably work. Thing of it is, I really do not want to see the fan go through the radiator and the bearings on this unit are showing a little side to side play.

The reason I think it is lack of fluid is when it is working it works fine. Then all of the sudden it will just not engage. Idle the engine down and wait a little bit and can hear the drive slowly pick up fan speed and then I can go back to work and the fan will be running full (or thereabouts) speed. I think by slowing the engine down, it lets the limited fluid left to seek where ever it needs to be to work. That's my theory anyway.

All this is a moot point for this tractor anyway. I already ordered the drive and it may be installed by now (been terribly sic today and didn't go into the shop). What I would like is to find an internet site or a big truck parts outlet that could cross reference the Eaton number cast into the drive housing and find them about half price of going through Deere. With bearing failure causing major radiator damage and down time probably would never modify an old one unless for a short time to get by while waiting on parts to arrive. 

Thanks for all the ideas.

John