overdrive in my opinion was an easy way for transmission makers to keep basically the same design and many of the same parts and add gearing to a transmission..
in effect im totally with you on the idea of being properly geared in the rear, having 5 underdrive hgears and a 6 at 1:1, that design keeps driveshaft RPM;s lower, still allows for 6 ranges of forward gears for proper acceleration etc..
but manufacturers wanted cheap.. so if they could take a Turbo 350 transmission or a C6, and simply add a gear.. then they still share parts with the predecessor that was still made.. (TH-350 / 700-R4), ( C6 / C6-4AOD), etc... and being allison ended up being placed in a lot of medium duty applications, things spilled over there as well in the later years,.
now that I have read about these early 6 speed MT's, i wonder now how we arrived at the current state of affairs with 3 underdrive, 1 1:1, and 2 overdrive gears in the modern allisons..
-Christopher
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