The 1st automatic transmission to use a torque converter (rather than a fluid coupling) was the Buick Dynaflow, which was introduced for that 1948 design yr. In typical driving, the Dynaflow made use of just the major gear, relying on the torque multiplication with the torque convertor at decrease speeds. https://gearbox-auto20853.blogozz.com/32938104/about-gearbox-auto