I have a 89 f-250 with the 7.3 idi and a zf5 trans. When I am cruising at 45mph there’s a loud grinding noise and it goes away after about 55 mph. It also goes away if I press the clutch in. It almost sounds like a bad belt squeal. Not sure where to look, im assuming I’m going to have to pull the trans figured I’d see if anyone dealt with the same issue before I start tearing into it.

 

You can start by checking the fluid in your ZF5. Here's a video I found with a quick search.

Source: YouTube https://share.google/3zJLvLe10qeJDX1eP

 

Will do thanks

 

I changed the fluid, it definitely needed to be changed it was brown and smelled like celery lol.