The main automatic transmission to make use of 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 used just the prime gear, depending on the torque multiplication from the torque convertor at decreased speeds. https://angelostsom.59bloggers.com/34231785/the-best-side-of-gearbox-auto