Type F is about the last of the unmodified AFTs.
All of the Dex/Merc and related ATFs are friction modified. The modified ATF's change the way the clutches and bands grab and hold. All things being equal, the clutches and bands will grab quicker and harder with an unmodified ATF than a modified ATF. (They also may effect the release)

Things have become far more complicated in recent years due to the computers for the automatics.
Dexron II or III is hard to find. Here's a repost from another list of my conclusions in 2008 as to
what commonly available fluid to put in a torqueflite 727 or 9xx.

Type F. It's in a category of its own.
The only unmodified atf with a dynamic coefficient that
increases as clutches and bands lock up - resulting in firmer shifts.
If that's what you need, great. Drawback is that the fluid doesn't hold
up as long.

Of the modified ATFs, the options in order of preference:
1. Dexron VI. This is GM's current standard. By definition, Dex VI is
fully synthetic and has the lowest low temperature viscosity. That's
great for street and the first autocross run of the day. However, what
convinced me that this is probably the best current replacement (unless
Type F is wanted) was that several manufacturers specifically list
it as backward compatible to Dex III *and* Dex II.

2. Synthetics. Several manufacturers offer synthetics labled as
appropriate for Dex III applications. e.g. Mobile 1 Synthetic, Castrol
Syntec, Valvoline Synpower. But it seemed that if the manufacturer offered a Dex VI,
they stated Dex VI is the prefered replacement. (Valvoline, Mobile)

3a Dexron/Mercon. These are probably all fine - especially if the trans
has some leaks - since its generally cheaper than options 1 & 2. A lot of
people who post on the web and seem to be knowledgeable like to point out that
Dexron III and earlier 'no longer exist'. What they mean is that
GM is no longer licensing the early versions, therefore what is being sold may
or may not meet the former Dex III standards. My feeling is that may be
technically true, but the companies have other incentives to make sure
these products are what they say they are.

3b Dexron/Mercon - a chronology. Gleanings from the web (which appear to be
more substantial than wild rumors, but you've been warned).
Dexron II 1973 - 1987
Dexron IIe was for electronic controls & had extra cleaning agents.
Mercon 1992- Contained less wax than Dexron
Dexron III c.1993 - Similar to Mercon. Lower low temperature
viscosity than earlier versions. Said to have better oxidation
resistance and improved seal life. Not all agree on the compatibility.

4. ATF+3, ATF+4. Similar to Dexron but formulated specifically for
Chrysler transmission control modules. All of the manufacturer spec
sheets I found on-line seemed to agree - NOT recommended for DEX 3
applications.

5. Mercon V. Seems to be the Ford version of Chrysler's ATF+. Also not
fully backward compatible.

6. Multi purpose: Probably the same as Dex/Merc, but better check the
manufacturers recommendations. Seems like too much of crapshoot for
people who care about how the autogear changer shifts.


These were my conclusions and obviously others may come to different conclusions. I've used Dex II and III, Type F, ATF+, Dex VI at one time or another in my own 727s. The only one that I was really unhappy with how it seemed to effect the shifting were the ATF+3/+4. I'm currently using Dex VI in the leak free trans and Dex/Merc in the Jeep with rear leak.
--
Matt
67 Barracuda nb 340 TF727
85 Grand? Wagoneer AMC 360 TF727 np229