Dexron III

Hello Bill,

From what I've discovered and understand, the Dexron III is "backwards compatible to 1949", see article excerpt copied from our MASTER FILE INDEX below:

regards, Paul



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Automatic Transmission Fluid (This is included because many of our old boats were specified to use ATF designations that are no longer available, such as the "TYPE-A" recommended by Chris Craft).

The first automatic transmissions of 65 years ago operated on motor oil that was dyed red to help identify leaks. Automatic transmission fluid (ATF) has since evolved into one of the most complex lubricants in the oil industry.

When engineers design an automatic transmission, they consider the frictional properties of the ATF. All ATF types fall into two groups-(hose that contain friction modifiers and those that don't. Friction-modified ATF reacts to lower the coefficient of static friction as a clutch or band locks up. This creates a very smooth shift. Unmodified ATF provides a higher coefficient of friction as the clutch or band locks up and creates a firmer shift.

The first friction-modified ATF was Type A, introduced as a GM spec in the mid-'50 s. It evolved to Type A, Suffix A and eventually to Dexron fluid, introduced by GM in 1967. The first unmodified ATF was Type F, introduced by Ford in 1959 and used in all Ford transmissions through 1976 (and severed after that date).

ATF choices stayed pretty simple through the '60s and '70s. At the end of the latter decade, however, variations in ATF were increasing. Dexron had evolved into Dexron-II, and Ford introduced Type CJ, a friction-modified ATF, in the late '70s. Ford also specified Types G and H fluid for specific transmissions. Types H and CJ didn't last very long, as Mercon was developed to reduce the number of fluids required for Ford products.

Mercon is a friction-modified fluid, similar to Dexron. Mercon specifically does not replace Type F or G fluids for transmissions requiring unmodified fluid. Mercon, however, is the preferred fluid for most 1983 and later Ford automatics, all Nissans and some Mazdas, Jeeps and Eagles. Dexron-II is a secondary recommendation or okay for topping up some transmissions. Today, Mercon-V is specified for some Ford transmissions, and Mercon-SP is used in some 2003 and later Ford trucks.

Be aware, though, that C4 and C3 transmissions through 1979 and 1980, respectively, require Type F. Also, Jatco transmissions in Courier trucks used Type F through 1982, and all FMXs required Type F until the last one was built in 1981. Starting to get confused? It gets worse.

Chrysler had long recommended Dexron-series fluids for its automatics, but it began specifying MOPAR ATF-Plus (Type 7176) for 1987 and later transmissions. This fluid evolved to ATF+3 and ATF+4. MOPAR ATF is friction-modified like Dexron but specifically formulated for the electronic control programs of Chrysler s transmission control modules (TCMs). The MOPAR fluids let the torque converter clutch work in a unique partial-lockup mode. Chrysler cautions that if the wrong ATF is installed, the TCM can't regulate partial-lockup slippage correctly. Result: converter clutch shudder.

The older fluid recommended by Mitsubishi and Hyundai, Diamond SP, was similar to Chrysler's ATF+3, but the Diamond SP2 is quite different.

Toyota is another carmaker noted for unique ATF requirements. Toyota calls for its own Type T or Type T-IV fluid in certain vehicles. Most notable among these are the all-wheel-drive Camrys and Corollas built in the late 1980s and early '90s. If you fill one of these transmissions with ATF other than the specified Toyota Type T, your customer will most likely have to buy a new trans in 5000 to 6000 miles.

Some disagreement currently surrounds the fourth generation of Dexron fluids. Dexron-III was introduced in 1995 to supersede previous Dexron varieties. GM considers Dexron-III a fill-for-life ATF for some late-model transmissions, and it has a couple of notable features. It greatly improves seal life and resists oxidation better than previous fluids. It also is formulated for the control programs of GM's transmission modules. It is, in fact, one of GM's attempts to eliminate torque converter lockup shudder.

GM says that Dexron-III is backwards-compatible with all GM automatics built since 1949. Other carmakers aren't so convinced. DaimlerChrysler continues to specify ATF-Plus and some proprietary Mercedes fluids for its vehicles. Many Asian carmakers continue to call for Dexron-II and specifically say not to use Dexron-III because of some reported shifting problems. Time and aftermarket economics will sort it out.
From simple Type A and Type F fluids of 40 years ago, ATF varieties have grown to no fewer than 15 specifications from 10 different car-building corporations. Don't try to memorize all of the details. Rely on your Chek-Chart specification guides from MOTOR to help you select the right fluid for your customers' vehicles.