[stevep]

Don,

Look at this:

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 1961-1964. It was based on the earlier, four-speed Hydramatic, but was more compact, providing only three forward speeds plus a small 8" fluid coupling with a stator 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 Super Turbine 300 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.


BTW, did you ever read the 1961 Hot Rod article where they installed washers in the pressure regulator valve to raise the line pressure and quicken the shifts? They did shave a bit off their ET, but I would love to have seen that coupling bowl after a few runs!!

One thing that we have seen over the years was that the Roto seemed to work better in an Olds than a Pontiac. A rebuilder who was around in the 50's-90's figured that because the Olds a bit more HP and torque, it worked better. We did far more Pontiac Roto's than Olds Roto's.