Dynaflow was the trademark name for an automatic transmission developed and built by General Motors' Buick Motor Division from the late 1940s to the mid 1960s.
Dynaflow, which was introduced for the 1948 model year, got some early, heavy-duty testing in the M18 Hellcat tank destroyers, built in Buick's Flint plant during World War II.
The Dynaflow initially used a five-element Torque (with two Turbines and two stators, and a planetary gearset), providing two forward speeds plus reverse. In normal driving, Dynaflow started in high gear (direct drive), using the converter for Torque multiplication. Low gear, obtained via the planetary gearset, could be manually engaged and held up to approximately 40 mph (65 km/h), improving acceleration, but the transmission would not automatically upshift to high gear.
Despite its smooth shifting capability, Dynaflow developed a reputation for being slow when compared to other GM divisions' Hydramatics and Chrysler's Torque. Dynaflow was also an inefficient transmission by virtue of its initial design. In 1953 Buick redesigned Dynaflow as the Twin Turbine Dynaflow, incorporating two turbines but only a single stator, which resulted in a higher level of performance and greater efficiency of transmitted energy. Buick also incorporated variable-pitch stators in 1955 for improved flexibility. A variant appeared in 1958, the Triple Turbine (Flight Pitch Dynaflow). This unit is similar to the Twin Turbine in theory, but bears many operational differences. A few indentifying features: Twin Turbine can be push-started, engages L up to 40 mph, and has a shift quadrant that reads P-N-D-L-R. Triple Turbine cannot be push started, engages low up to 45 mph, and has a shift quadrant that reads P-R-N-D-G (where "G" stands for Grade Retard).
The Dynaflows were discontinued in favor of the Super Turbine 300 two-speed and the much more efficient Super Turbine 400 three-speed automatics (the latter being Buick's trade name for the Turbo-Hydramatic) starting in 1964. Elements of the Dynaflow continued a few years longer, as full-size Buicks (along with full-size Oldsmobiles and some Cadillacs) used a variable-pitch torque converter variant of the Turbo Hydramatic from 1965 through 1967.