The first automatic transmission to utilize a torque converter (rather than a fluid coupling) was the Buick Dynaflow, which was launched for your 1948 model year. In regular driving, the Dynaflow made use of just the best gear, counting on the torque multiplication with the torque convertor at reduced speeds. https://gearboxauto93692.theideasblog.com/34277008/detailed-notes-on-gearbox-auto