The main automatic transmission to use a torque converter (rather than a fluid coupling) was the Buick Dynaflow, which was introduced for that 1948 model yr. In typical driving, the Dynaflow made use of just the prime gear, counting on the torque multiplication on the torque convertor at reduced speeds. https://gearbox-auto30741.is-blog.com/40292897/facts-about-gearbox-auto-revealed