Changing fluid (and filter) in my ’66 Toronado and wondering if using Valvoline Max life synthetic fluid is acceptable for this transmission? It is a multi-vehicle blend, for GM Dexron II, III, and IV etc. Some say using synthetic fluid in older transmission can cause leaks so wondering what others have to say about it? Also, is it safe to add it to what old conventional Dexron does drain out?

n’t drain out in during the change?,,,

 

I would put Dexron III/Mercon in it if you can find it.

I would stay away from anything synthetic unless the transmission has been recently rebuilt with parts compatible with it. Contrary to what a lot of folks say synthetic isn't compatible with 60s vintage clutch materials.

 

Thanks for your reply. I read many places that the Ford F type fluid is a good replacement for the Dexron III,,,

 

Again, ONLY if the transmission has been rebuilt and is dry before you put the Type F in it. F has different friction characteristics than Dexron or any synthetic and may not mix well with any existing Dexron in the transmission.

 

A lot of people use Type F, it can be mixed with Dexron. It will firm up your shifts.

 

Did that in a couple of high-mile Turbo 350s with no ill effects.

Tried it in a Toronado's 60k mile 425 and immediately after the drain and refill with Type F the 2-3 shift went from quick and positive to a drawn-out shift with engine flare. Coincidence? Maybe. But I've been wary of mixing different fluids since then. A 425 was a $1300 rebuild in 1990.

 

It will work fine.

Gesr changes are accomplished by hydraulically clamping friction plates together. As long as the pump can provide enough pressure, and the friction material has enough surface area to provide sufficient grip, the type of fluid has little influence.

The fluids purpose is mainly cooling and the pressure. And I have never put too much faith in the mixing of conventional and synthetic fluid causing leaks.

 

Stick with Dexron III / Mercon.
It's what this transmission was built to use, and is a safe bet.
Anything else is a crapshoot.

 

Even though I have 3 gal. of the multi-vehicle Valvoline in stock for other vehicles and also several quarts of Ford F type for my old Thunderbird, all things considered it sounds like sticking with Dexron III is the safest bet,,,thanks to all made suggestions!