GM Roto Hydramatic transmission

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Roto Hydramatic (sometimes spelled Roto Hydra-Matic or Roto-Hydramatic) was an automatic transmission built by General Motors and used on some Oldsmobile and Pontiac models from 1961 to 1964. It was based on the earlier, four-speed Hydramatic, but was more compact, providing only three forward speeds plus a small torque converter in place of the Hydramatic's fluid coupling. Oldsmobile, one of the users of this transmission, called the torque converter's stator the "Accel-A-Rotor." The lightweight, aluminum-cased transmission was sometimes nicknamed the "Slim Jim."

There were two models of the Roto Hydramatic: the lightweight Model 5, which weighed 145 lb (66 kg) and had ratios of 3.03, 1.58, and 1.00, and the larger Model 10, which weighed 154 lb (70 kg) and had ratios of 2.93, 1.56, and 1.00. The stator provided a maximum torque multiplication of 1.2:1. In 1961-62 the "Model 5" was used on the Opel Kapitan, Vauxhall Velox/Cresta and EK Holden. The Roto Hydramatic was cheaper and smoother than the previous Hydramatic, but its slower, softer shifts sacrificed performance for refinement. Owners discovered that it was also less durable than Hydramatic, and was prone to various mechanical problems.

The Roto Hydramatic was phased out after the 1964 model year in favor of the two-speed Jetaway and three-speed Turbo-Hydramatic. As with previous Hydramatic transmissions, auto safety experts criticized GM for the Hydramatic design which had a shift quadrant sequence of Park-Neutral-Drive-Second-Low-Reverse (P-N-D-S-L-R) due to the placement of reverse adjacent to a forward gear as opposed to the more common P-R-N-D-S-L sequence found in most other automatic transmissions at the time that placed "reverse" between "park" and "neutral", which was also incorporated in the new Turbo Hydramatic design introduced on Buicks and Cadillacs in 1964, and then other GM divisions in 1965. The Roto Hydramatic was used in all full-sized Oldsmobile models including the Dynamic 88, Super 88, Ninety-Eight and Starfire from 1961 to 1964 as well as the compact Oldsmobile F-85 from 1961 to 1963. Pontiac used the Roto Hydramatic from 1961 to 1964 on its shorter-wheelbase full-sized cars including the Catalina, Ventura and Grand Prix, but continued with the older four-speed Super Hydramatic design in the longer-wheelbase Star Chief and Bonneville models.