I heard back in the day one of the two is more acidic than the other. I don't remember which one it was. But I can tell you type "F" gave firmer shifts. This is why Ford switched fluids in the C6 circa 1977. To give them a softer, more cushy cushy shift. As to finding out what a PO put in....I would locate a local Lab that can analyze the existing fluid. As we have mentioned in previous threads when a tranny is built it's friction discs are soaked in whatever fluid is going to be filled in the tranny. Now the fluid can't be mixed or changed. Unless a total tear down and clean. Others on this Forum have tried it only to have their tranny (the friction discs) slip.

 

That's it in a nut shell. You have to know what is in it and use the same stuff. Or you will be doing an overhaul shortly. Ya can't mix them and ya can't just drain it or even flush it and change types. It all depends on what the disks were first soaked in when it was assembled.

 

I'm tempted to just do a tranny service with Type F, but I know I should probably send a sample in for analysis.

Seems like it would be a gamble to put the Dexron in, but a safe bet for a tranny with a shift kit to use Type F.

 

The shift kits I have been around back in the day was just mods to the valve body and didn't get any clutches. So it had to use the same fluid as it had. We would use C6's with Type F because they shifted firmer and lasted longer at our street drag strip.

 

The dipstick should say on it what fluid Was supposed to be used. "In theory" the PO would have gone by that. But it's still a gamble untill you send a sample out.

 

I don't see the logic in using anything other than type F in it. A shift kit wouldn't change that either.

I'm still trying to decide what I will use When I swap my AOD into the truck, I could use Mercon, since that's what it was designed to run, or I could use type F for firmer shifting and less slipping.

 

I'd go with what it says on the dipstick. That way some dipstick won't put the wrong fluid in it when you aren't looking.

 

That's my thinking too. Plus, Mercon is a lot easier to come by than type f...

 

I've never been in an auto parts store that didn't have Type F. Lordco gave me a really weird look when I asked for a whole case of it, hahaha.

Fun fact. Mix Type F with Acetone 50/50 and you now have the world's best penetrating fluid.

 

Almost every parts store has it, but in limited supply. When I worked at oreillys we only had maybe 12qts on hand at most. And only one brand. Mercon was stocked in quarts, gallons, cases, and in 5 different brands.

 

The local car scene here is classic muscle. It's easier to find stuff ford old cars than new cars.