The more I hear about this, the more I suspect the hydraulic fluid used.
Maybe that’s the binding Fordtech86 originally suspected. Could it be happening in the HST itself, thus causing the black smoke??
I wouldn’t use that fluid in my HST tractor, for fear of similar results.
Seems like the problem started with the fluid change when Ferguson got the tractor?
No idea if I’m right. Just a guess. I know some will say don’t worry about it
Ferguson- I hope you find the problem, and my best wishes in getting it fixed. It looks like you’ve done a great job trying to figure it out.