The main automatic transmission to utilize a torque converter (in lieu of a fluid coupling) was the Buick Dynaflow, which was launched to the 1948 design yr. In regular driving, the Dynaflow used only the top rated gear, depending on the torque multiplication with the torque convertor at reduced speeds. https://gearboxauto04701.blogrenanda.com/40073481/how-gearbox-auto-can-save-you-time-stress-and-money