The very first automatic transmission to use a torque converter (instead of a fluid coupling) was the Buick Dynaflow, which was released for that 1948 model calendar year. In usual driving, the Dynaflow employed just the prime gear, depending on the torque multiplication in the torque convertor at lower speeds. https://gearbox-auto52962.azzablog.com/34315137/gearbox-auto-for-dummies