Ford ZF manuals shifting worse after Amsoil synthetic fluid change. Suggestions?

Jan 25, 2022
I recently changed oil in my 1997 F350 (60k miles) with a ZF5 and a 2004 F250 (120k miles) with a ZF6 manual (both gas engines). Both of these operated and shifted flawlessly before and the fluid changes were both done as preventative maintenance. I filled them both with Amsoil Torque-Drive syn ATF. Afterwards neither one shifts as well and are especially hard to get into gear when cold. Also the shifts now feel clunky like the fluid is thin and the shifts feel borderline scratchy. I feel I should change to a different fluid or add something but what?
Not that I'd know what is going on here in your trannies.
What fluid was in the tranny's prior to the Amsoil? You may want to switch back.
What does FORD recommend?
Clearly, I'd switch back to what Ford recommends. Did Amsoil actually
recommend using 'Torque-Drive syn ATF' for these applications?
Ford/Motorcraft sell some really good MTF that's well regarded even
from other make owners. Don't MX-5 owner swear by Motorcraft MTF?
The book actually specs for ATF on both and to my knowledge I think I drained the factory original fluid. Amsoil specs this oil for the application. All I could do is try going back to a conventional ATF unless I try a different fluid outside the spec.
The wife had a 2002 7.3 with the 6 speed and running Redline D4 or Mobil 1 syn I didn't notice any difference in shift quality. Changing the oil would be the only option.
Hmmm. The Torque-Drive has about the same high temp viscosity and a better cold temp Brookfield viscosity than the Mercon V.

The Torque-Drive also has about the same Mu(v) or friction modification as the Mercon V, so I don't know why it would shift differently, except that most of the nation is experiencing cold temps. Where are you located and what are the temps?
Personally, I would put some miles on and see if maybe they don't just start to behave better. I really don't think minor differences between the Motorcraft and Amsoil ATF would in any way harm them. Chances are fresh Motorcraft Dexron V would feel similar to the Amsoil.
Only difference I can think of, besides the obvious truck/bus slant of Torque-Drive(it’s tested for but not vetted by Allison/ZF/Voith for use on heavy-duty automatics) is the base oil composition of it. Mercon V is a “enhanced” Mercon Ford still licenses out.

I’m guessing the synchro material is being fussy.
If I remember correctly the late 90's ZF5 calls for plain old Mercon V. XT5QSM
The owners manual calls for Mercon, XT-2-QDX, not Mercon V. The product is now typically sold as “Dex-Merc” by various suppliers. Although Ford back specs Mercon V maybe in this case it’s better to use the old Mercon.

Here are the excerpts from the owners manuals. The first one is the 1997. Enjoy.

Last edited:
This is from Amsoil. Says it’s good for Mercon V applications. Ford calls for Mercon, not Mercon V. Although Ford might say Mercon V is back spec’d to work in automatic transmissions originally spec’d for Mercon, the OP seems to be having some problems with the ZF’s and the Mercon V equivalent Amsoil product. Maybe change back to a Dex-Merc product.

Last edited: