When I first installed it, there was a whirring sound. New input bearing, new clutch assembly, BC ZF install kit and junkyard 89 F-250 ZF S42, just the back story.
It sat for two months while I was doing body and cage work. Started it and now all the racket it is loud like the transmission is tearing itself apart. The wife even asked if there was something wrong with the Bronco. Although still seems to shift fine.
It seems all my co-workers are a new car crowd and not alot of older F-250's running around to compare the sound of their ZF noise.
A long time ago I drove an Army buddies truck with the ZF and you could hear the transmission but, it was nothing like this. Or so I remember.
I have the Haynes manual for the year model F-250 I pulled the trans from and it said " noisy in neutral engine running" Input shaft bearing worn, damaged main drive gear bearing, worn countershaft bearings, or worn or damaged countershaft endplay shims.
I hear the folks say just run it but, I think the noise it is making is a little more than transmission noise, maybe?
In the end I am not a mechanic and have made it through all of my Bronco repairs by reading the book on the fender as I am doing it.%)
So run it or rebuild it, I guess I could just pad the heck out of the trans tunnel and wear ear plugs!