The main automatic transmission to use a torque converter (as opposed to a fluid coupling) was the Buick Dynaflow, which was released for that 1948 design calendar year. In standard driving, the Dynaflow applied just the top gear, relying on the torque multiplication on the torque convertor at lower speeds. https://gearbox-auto37813.blogripley.com/34470807/the-basic-principles-of-gearbox-auto