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The Roto-Hydramatic debuted in 1961. From the 1961 service manual:
"Two planetary units are used to obtain neutral, three forward speeds, and reverse."
"A fluid coupling is used to provide additional torque multiplication for first and reverse gears and to lock members of the two planetary gear sets together to provide third speed (direct drive). A multiple disc clutch is used to lock the drive torus and front unit internal gear together to provide reduction in the front unit for second speed. This clutch is also used with the fluid coupling to lock the front and rear units together to provide third speed (direct drive)."
"A sprag clutch is used to lock one member of the front or rear unit to the case to provide reduction for first and second speeds."
In 1961, when the fluid coupling empties, this is called the 1-2 shift. In 1962 this is called the 2-3 shift. I have long been under the impression that the change in '62 was a marketing ploy by GM.
Between spares & units installed in cars I own seven 1961-2 Slim Jims. They look & perform exactly the same. Was the Slim-Jim redesigned so extensively between '61 & '62 that the torque multiplication of the rotor became a separate stage or speed? What changed, engineering or marketing? Please shine some light on my misinterpretations.
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