I grew up around the first shop in Nashville Tennessee to work on automatic transmissions, and attended a GM-sponsored seminar Dad was teaching for area mechanics on the Dual Range HydraMatic. At the ripe old age of 12, GM sent me a certificate proclaiming to the world that I was a "Certified Hydra-Matic Technician".
The Dual Range transmission used in the mid-1950's Chevy and GMC trucks was the second-generation transmission- - - -the first one that was produced from 1940 to around 1952 did not have the 3rd. gear hold position on the shift quadrant that locked the box out of 4th. gear until the engine was almost ready to float valves. The 1939 transmission had 4 forward speeds that shifted automatically, but it also had a manual clutch. Stopping and starting required the driver to disengage the clutch to prevent stalling the engine. By 1940 they had figured out how to include a fluid coupling (not a torque converter) that allowed the engine to idle in gear. Thousands of WW II military trucks ran Hydramatics, along with a light tank that ran two Cadillac flathead V8's with a H-M for each track. Dad's only competition in the automatic transmission business in the late 1940's and early 50's was a former tank mechanic.
Lots of history there- - - -I encourage you to keep the automatic unless it's trashed. FATSCO transmissions up in Noo Joisey still stocks a good supply of repair parts.
Jerry
