In 1961, General Motors introduced one of the most unusual automatic transmissions the Motor CIty has ever seen: the Buick Special Dual Path Turbine Drive.

At General Motors, Buick had a tradition of going its own way on automatic transmsissions starting in 1948 when, instead of adopting the corporate Hydra-Matic like Oldsmobile, Cadillac, and Pontiac, it introduced its own unique automatic, the Dynaflow. That approach was still evident in 1961 when the compact Buick Special was introduced, and with it Dual Path Turbine Drive. Used only in the 1961-63 Special and Skylark, this two-speed gearbox was like no other automatic transmission produced by GM before or since.

Dual Path referred to the fact that engine torque was split between the torque converter and the output shaft. And just as the illustrations suggest, the transmission was designed to be as light and short as possible—total weight was around 95 lbs, around half that of a Hydra-Matic or Dynaflow, and compared to these transmissions, it’s tiny.

Like the Chevrolet Powerglide, the Buick two-speed used a three-element torque converter and a single planetary gearset, but it shared no components with its GM sibling and was laid out in a totally different way. Here, the torque converter was installed backward from the conventional layout in the air-cooled aluminum case, with the impeller toward the flywheel. Meanwhile, the gearset was iocated inside the converter. (See cutaway above.) Additionally, the Dual Path Turbine Drive incorporated a torque converter clutch, aka lockup torque converter, a feature that would later become universal on Detroit automatics in the CAFE fuel economy era.

The valve body, clutches, and centrifugal governor were in the conventional location behind the torque converter, more or less, operating the planetary gearset and torque converter clutch through a series of four sleeve-shafts, one inside the other, that were concentric to the mainshaft. Clutch applications through the sleeve-shafts selected low gear, high gear, neutral, and the torque converter clutch. While the four concentric sleeve-shafts might seem a bit Rube Goldberg, the setup was actually quite ingenious.

With most of its business packed inside the finned torque converter housing (above) the Dual Path Turbine Drive was a compact and efficient package. And by most accounts it worked pretty slick, with smooth shifts, good acceleration, and industry-standard reliability. (Though parts are difficult to find today.) But since the transmission was used only in the Buick Special and Skylark and shared no components with other GM products, its cost must have been difficult to justify and the Dual Path Turbine Drive was discontinued at the end of 1963, when the Dynaflow was discontinued as well. From 1964 on, Buick used GM’s corporate automatic transmissions.

1962 Buick Special Deluxe Convertible