FAQ: Should I use synthetic fluids in my transmission or differential?

I have had some experience with synthetic fluids, such as Amsoil, Mobile 1, etc. I believe that synthetic engine oil works better than "regular" engine oil, reducing friction noticably, and for this reason I would say yes to a question about using sythetics in an engine. An automatic transmission, however, relies heavily on properties in the fluid to make proper shift quality, and in all of my personal experiences concerning synthetics in an automatic transmission, shift quality suffered substantially. Honda, Chrysler, as well as other manufactures, are now manufacturing their own fluid that they design their transmissions around. Using Dexron III in a Honda/Acura, or Chrysler, can, and do, cause various shift complaints that Chrysler's "7176", and Honda's equivalent, prevent. I have seen synthetics cause much more pronounced shift-quality-based complaints than merely substituting Dexron III for "7176" fluid. A problem also can result from using synthetic lubricant in a limited slip differential, rendering the limited slip clutches almost completely useless. I do not recommend the addition of synthetic oil in any automatic transmission, or limited slip differential.
As for installing synthetic fluids in a standard (open) differential, transfercases without any kind of clutch-type coupling, or standard transmissions that do not have "special" syncros (most syncros are made of brass material, but many are changing to fibre syncros that work similar to automatic transmission clutches; with these new type transmissions, I do not recommend synthetics.), you can without any negative results, aside from the price. For these components, I do not recommend synthetics, but it cannot hurt; Use your own judgement. If it makes you feel better, then by all means, use synthetic oil.