The Hydra-Matic was one of the most "over-engineered" transmissions I've ever worked on. For instance, it has two hydraulic pressure pumps, one driven by the engine, and another that's connected to the output shaft. Theoretically, that was done so hydraulic pressure to apply the clutches and bands could be developed by pushing the vehicle above 30 MPH- - - - -in case of a dead battery. However, there's an additional advantage- - - - -above certain vehicle speeds, the rear pump generates enough fluid volume that the variable-displacement front pump moves "over center" and acts as a pressure relief for the rear pump- - - - -effectively taking the load of generating hydraulic pressure in the transmission off the engine. There's a good reason Rolls-Royce licensed the production of Hydra-Matic transmissions for their own vehicles.
Jerry
