The main automatic transmission to use a torque converter (rather than a fluid coupling) was the Buick Dynaflow, which was introduced for your 1948 design calendar year. In standard driving, the Dynaflow used only the top rated gear, relying on the torque multiplication of the torque convertor at lower speeds. https://collinrwvsn.digitollblog.com/33962380/a-review-of-gearbox-auto