727 Fluid- What and Why?

No problem mixing fluids, my personal mix is a 50/50 blend of Dexron and Type F.

I use type F to protect the clutches, they are the most common failure I see by a long shot, bearings and gears not so much. The type F allows the clutches to live longer, +4 is to make soft shifts and protect bearings and gears. In reality the difference is barely noticable from type F to +4. All the dex merc stuff seems to be somewhere in the middle and you should have no issues mixing them.

My Chrysler has the original 1969 transmission, less than 60,000 miles. I know I had it changed at ~ 52,000 miles but it's been about 10 years now and the gasket is leaking again. What do you think would be best for my situation? We don't drive it hard at all and almost no highway driving.

Robert

Type F.

ATF+4

ATF+4 is formulated for transmissions with lockup converters and overdrive gears that run constantly...not features that you find in the majority of performance 727's.

Although Mopar says it is backwards compatible with previous fluids and recommends it for older 727's they do that mostly to be able to stock just one fluid in their service/parts departments rather than 3 or 4.

For torqueflite 727 and 9XX transmisions, Chrysler changed recommendations as fluid improved.
About 2/3 way down in this 2002 Motor Magazine article they summarize the differences in ATF up to 2002.

Type F has the opposite characteristics than most of the other fluids. Many racers have used it in torqueflites for that reason.

My conclusions that the 'best' claims to backword compatible ATF for a plain 'A' or 'Dexron' spec'd torqueflite are:
Dexron VI (synthetic and generally most expensive)
Synthetic Dexron spec'd as Dex III replacement
Dexron/Mercon (least expensive)
Multi-purpose (usually least expensive, but IMO these are a crap shoot on compatibility)

The newer ATFs usually have better oxidation resistance and low temperature viscosity. Whatever you buy, check the can (uh bottle) or the manufacturer that its compatible with Dex II or earlier.

Warning: Some bottles say compatible with all Chrysler transmissions. This is a bad sign. The needs of all Chrysler transmissions are not the same. Many do not take Dex III and earlier. There are long articles on this (go to Allpar.com for an example). As stated by others, the big change in Chrysler ATF seems to be when ATF+3 and +4 were developed specificly for the new transmissions with control modules.

Another moparts thread on Dexron and Type F characteristics In it, an oil dealer posts some of the viscosity specs for Dex VI, Dex III, and F synthetics in his product line. Note that this specs, especially for Dex III and Type F may not be the same as other brands, but it is a good way to see one way these ATFs are different.

edit corrected link

All I can tell you is that many years back I had an old beat up Mopar wagon with a 383, 727. The trans started slipping between gears when it shifted. I was using the old wagon to pull the dirt tract car to the track, and it was racing season, no time to fix the hauler! So like a good boy, I dropped the pan, scrapped all the "stuff" out of the pan, changed the filter and added the Dextron fluid. The slip was still there. My friend that worked on transmissions suggested I try the Ford fluid, so I dropped the pan, replaced the filter again, and filled it up with the Ford fluid. The trans quit slipping, and we got another year out of it pulling the race car before something else went out in the old wagon. Without a doubt, the Ford fluid helps the clutch linings.
I've used Ford fluid in all my non-OD transmissions since. The newer OD stuff gets the ATF+4. Gene

Great debate! I have always run Type F, but got a new Turbo Action converter and it listed +4 as the first choice and Type F as the second. I filled the converter with F upon install,but haven't filled the trans yet...thought I'd ask and see what I don't know about ATF.

I had a fellow that did my trans work a while back tell me just use red fluid!!! Just go buy the cheapest red fluid you can find and run it. Did that and never had a problem so

I just got my trans done.. Trans guy said to use type f... Convertor I bought tci? said to use red fluid/. I bought the f. Kevin