Hi, I have a 01 Superduty with a ZF6, 268,000 miles. I am using regular ole ATF. I want to change the oil soon, and would like know what has been working in there?
I have a grinding when I try to downshift into 1st, or whatever you want to call, the normal take off gear ( not the granny gear opposite of reverse/granny gate ).
I have used Pennzoil synchromesh, in other applications that has worked well, in backlash, not preload transmissions, like the ZF6.
Any ideas? Thanks, Artie

 

At the risk of starting another oil debate; I changed mine to Redline Synthetic ATF. It may be my imagination, but it seemed to shift smoother and I eliminated the rollover (klack klack) when you push in the clutch after being under load: Red Line Synthetic Oil - Automatic Transmission Fluids - D4 ATF

 

I use Amsoil full synthetic ATF, but do have gear roll over when towing heavy at various times. Although, since I bought the truck a year and a half ago and changed the fluid twice, the gear roll over is not as bad as it used to be.