I use type F fluid in my TH350. At first I was skeptical but I did it and it works fine. They say Dectron is made to give a softer shift while Type F has less slippage and allows the tranny to shift harder. From now on I will only use Type F in all my trannies. Try it, it works.
409SB, TH350, 12bolt 4.10
7.18 @ 95 on premium pump gas
<BLOCKQUOTE>quote:</font><HR>Originally posted by ChevyCam: My built th400 instruction sheet recommended Type F tranny fluid anything else would void warranty. They specifically said to stay away from all newer dextrons. No problems so far!
At one time the oil types were to prevent seal and friction material problems. Apparently the different oils weren't compatible with various friction materials and seals used at the time. Now I think all seals and plate materials are pretty much the same. The difference comes down to adhesion modifiers, defoaming adgents and that sort of stuff. I've heard lots of people using Type F, but I have always stuck with Dextron II / III mainly because I was afraid to try anything else. However I don't think you'll have any of the seal / plate problems that was originally an issue. I'm not sure about mixing types though. If you're doing a fluid change, there will still be several quarts of the old stuff in the converter.
First a history lesson. Type F oil was used up until 1976 by Ford. Up to that point is was an everyday experience to work on Ford trannies that came in with this thick, stinky varnish that used to be oil. You see, Type F was and IS an inferior oil that does NOT hold up to heat. This makes it a particularly bad choice for newer vehicles as they all run allot hotter now. I would also stay away from any oil that is supposed to make a tranny shift 'harder', that is the job of the trannies calibration where the oil's job is to transfer power and lubricate and COOL the tranny. If heat and/or lubrication is an issue I use full Synthetic oil. If you are after a firmer shifting tranny then get a Valve Body kit. IF you ALSO want the tranny to last longer and FIX common problems then get the TransGo Shift kit or Reprogramming Kit.
For direct tranny questions: E-mail with subject "tranny problems"