The 1st automatic transmission to use a torque converter (as an alternative to a fluid coupling) was the Buick Dynaflow, which was released for your 1948 model year. In regular driving, the Dynaflow employed only the best gear, counting on the torque multiplication in the torque convertor at reduce speeds. https://gearbox-auto31963.blogs100.com/34273652/indicators-on-gearbox-auto-you-should-know