Ford C4 recommendations please

[JackFish]

Hello again, it's time for a filter and fluid change for my 1978 C4 auto. The manual calls for type "F", but I'd like to try a synthetic.
Price is not an issue, I just want the "best" in terms of smoothness, and the fact this is an old transmission and could probably use a healthy dose of additives.
Is a flush necessary? I plan to drop the pan.

 

[Torino]

JPT transmissions in Michigan recommends 0-20 Mobil-1. They are the gurus for C-4's. Specialty Formulations will make up a mix for your specific needs. I personally use OTC Type-F but change it out completely (67 Mustang, so I have the converter drain plugs) which simplifies the routine. My change interval is once a year--approx. 5000 mi. Best regards. John. Las Vegas.

 

[ConfederateTyrant]

Amsoil Supershift (ART), it's recommended as a Ford type F and Allison C-4 replacement, http://www.amsoil.com/storefront/art.aspx

The fluid is compatible with whichever Type F that is currrently in there, so a flush would not be entirely necessary unless you're hoping to get at least 90% of the fluid replaced.

 

[unDummy]

A flush isn't necessary but recommended. You should rotate the TC to see if you have a TC drainplug. This way, you won't need to do a flush. A pan drop + torque converter draining is a ~full fluid change.

Even though you don't need a full synthetic, here are some:
Redline Racing ATF
Amsoil Supershift
SpecialtyFormulations SFRglide

Since this is an old tranny, and you didn't mention previous rebuilds/mods/maintenance history, I would just use the cheapest TypeF that you can find.

C6's aren't meant to be smooth. Replace your vacuum modulator and adjust the kickdown rod/cable.

 

[Pablo]

Go with:

ART

 

[JackFish]

Thanks for the input guys.
I'm hoping that the synthetic might give a couple of extra HP back by way of superior lubrication.
I haven't checked yet, but I'm pretty sure the torque converter has an accessible drain plug.
The engine's a straight six with the high-mount starter.