The main automatic transmission to work with a torque converter (as opposed to a fluid coupling) was the Buick Dynaflow, which was introduced for your 1948 model year. In standard driving, the Dynaflow used only the top gear, depending on the torque multiplication from the torque convertor at reduced speeds. https://gearboxauto65206.blogripley.com/34471273/the-best-side-of-gearbox-auto