Overdrive for Dyna Flows?

[suntreemcanic]

I was talking to an older gentlemen last week and he remembered overdrives for Buick Dyna Flow transmissions. I have never heard of anything like that, has anyone else? Maybe in the rear end? Vacuum two speed like the old two ton trucks had? If there was such a devise---- 3:90 gears and some road speed!

[BornBuick]

… late to the party here but dynaflows are like a fluid coupling and has multiple multiplication factors for ratios to a practical infinity. This means unlike other automatic transmission, the dynaflow never really shifts but continues to multiply it's spin and toque curve in a aspect ratio to ground speed. Therefore a overdrive was never needed so this old guy was confused. Overdrive units back in the day were connected to manual transmissions. The overdrives on present day automatic transmissions are electronic in nature and of a completely different horse altogether.