Street car, has a fully rebuilt TH400 and I will be running one of Jim's TSP converters. Trans mechanic said I can use whatever fluid floats my boat. I understand Dex 6 is much thinner viscosity than Dex 3 however Dex 6 has a longer service life. This is going to be driven maybe 3000-5000 miles a year and is primarily a street car. So, what would you guys pour into your fresh trans, III or VI ? PS, does brand matter? I know I can spend $12 a quart on fancy synthetic, but I want something that is common and simple for the poor fool (my son) who will own this car after I'm dead.
I would use either plan dex/merc of old fashioned type f. Just be clear to you son what fluid is in there. I don't see the need to pay crazy fluid price for this
I use Valvoline Max Life in both my GS and 98 Riviera. My Riviera has 200,000 miles on the original 4T65HD transmission. Still shifts great. The GS has 589 ft. lbs, and one of Jim's 9.5 converters. The Max Life ATF is full synthetic and Dex 6. https://www.valvoline.com/en-thailand/our-products/automatic-transmission-oil/maxlife-atf
I also use the Valvoline max life synthetic. It’s on sale right now at AutoZone for 23 bucks a gallon. Hard to beat that price for a synthetic fluid.
I was told a long time ago to use Type F by TCI?? I do know type F has a higher viscosity than Dexron resulting in a higher line presure, which results in less slip and firmer shifts like said above. With that said, Larry mentioned Max Life fully synyhetic. That covers almost all trans fluid specs...