Quote:
Originally Posted by Schurkey
That's probably why they have four speeds, instead of three--no torque multiplication from a torque converter, just slip from a fluid coupling. The later unit had two fluid couplings--the main one in front, about the same size as a typical torque converter, plus another that took the place of a clutch-pack. About 8" diameter, with a fill-and-drain scheme to mimic a clutch pack applying and releasing.
It's no wonder that the Turbo-Hydramatic 400/Super Turbine 400 was such a ginormous improvement in sophistication from the day it debuted in Model Year '64.
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Reply's like this are why 4 speed hydros get a bad rap because people don't understand them. The torus slips at idle, which quickly diminished at very low speeds. This was purposely engineered for an exceptionally smooth startup by the input torus of the fluid coupling running at a slower speed than the engine due to the reduction of the forward gear assembly. Slippage is almost negligible after shifting into 2nd gear. Between this design and the split torque design, these early hydros are
documented as being the most efficient automatic transmissions in existence until lockup torque converters came into play in the late 70's/early 80's. The 350/400 transmissions are more
INefficient than the first dual band transmission in 1939.
GM switched to the Turbo Hydros because they were simpler, lighter, and
cheaper to manufacture. The dual band/dual coupling hydros were a true GM design from start to finish by Earl A. Thompson, a Cadillac engineer. The Turbo Hydros were a Simpson based design first licensed by Chrysler (Torqueflite) and later by Ford (Cruise-O-Matic).