Just a few thoughts regarding auto trans fluids.....
1. The concept of friction as it applies to tranny fluid is totally different that oil: with oil you theoretically want the lowest friction since friction increases losses in your engine output. with an automatic transmission, the friction coefficient of the fluid applies almost entirely to the fluid's action with the clutches - allowing the clutches to grab or slip based on the engineering parameters established at design time. the role of atf is: - hydraulic fluid - to clean - to cool - to lubricate - to seal each tranny builder sets up a fluid spec that is composed of many parameters - and each fluid (Dexron III, Dexron V, Mercon, ATF+4, etc) must meet those specs. certainly there are different qualties of fluids: some handling heat better than others, and some staying in spec longer. unfortunately most of that is masked in marketing and its hard for people to know the truth. from your sig it appears that you are using Amsoil ATF. I believe that you have made a sound choice - Amsoil's ability to handle heat and not shear makes it a top quality fluid. I use it in my all my cars, including my Ram that pulls over 10,000 lbs. the truck is 11 years old and has never had a tranny problem. and as long as Amsoil meets Chryslers ATF+X spec (because their trannys were one of the first to use electronic shifting and are very sensitive to the fluid friction properties) I am very happy!
2. For one thing, small differences are important. For another, its not JUST the "coefficient of friction" that matters, and CF itself isn't just one number. In the case of ATF+4, what matters most is that the sliding (dynamic) and still (static) coefficients of friction be as close to one another as possible. If the static CF is much greater than the dynamic CF, then what happens as a clutch engages is that just before its fully engaged, the static CF takes over and the clutch "grabs." The sudden loading of the grabbing action then starts the clutch slipping again at the lower dynamic CF, and then the "grab" occurs again. This is what causes torque converter clutch "shudder" and why ATF+3 (and +4) were designed the way they are. If the static CF is very very close to the dynamic CF, then there's no sudden "grab" as the clutch engages.
3. The first thing that you have to understand is that the whole friction discussion is much more complex than just a question of fluid choice. In an automatic transmission for instance the determination of 'appropriate' friction behaviour is down to a combination of the friction materials used, not only for shift clutches but also for TTCs, reaction surfaces, control systems, and last but by no means least, the fluid. Given that it is probably easy to see that a fluid that performs well in one situation might not work very well in another.
How can all these multi vehicle ATF's perform in so many different applications? The properties have to be very close to the same. If you had a Honda and Z-1 was not available what ATF fluid would you use as a replacement? MecronV,ATF+4,DexronVI There is no one super fluid to cover every application except maybe Amsoil ATF which seems to claim nearly every application.
I guess the final determination is by the owner, and his/her own judgement as to which fluid is "best"....it seems as if which fluid is in use, by who ever is using it, is the best fluid.....probably using the time honored methodology of "seat of the pants feel" (#11) or maybe its the color, taste, smell, or price...or ??.....for those keeping score, ATF+4 seems to be the winner.........just talking out loud......
BOB RENTON
