Dynaflow

Dynaflow was the trademark name for a type of automatic transmission developed and built by General Motors' Buick Motor Division from the late 1940s to the mid 1960s. The Dynaflow, which was introduced for the 1948 model year only as an option on Roadmaster models, received some severe early testing in the M18 Hellcat tank destroyer, which were built in Buick's Flint, Michigan assembly plant during World War II.

The Dynaflow initially used a five-element torque converter, with two turbines and two stators, as well as a planetary gearset that provided two forward speeds plus reverse. In normal driving, Dynaflow started in high gear (direct drive), relying on the converter's torque multiplication to accelerate the vehicle. Low gear, obtained via the planetary gearset, could be manually engaged and held up to approximately 40 miles per hour (65 kilometers per hour), improving acceleration. However, the transmission was incapable of automatic shifting, requiring the driver to move the shift lever from low to drive to cause an upshift.

The Dynaflow was an inherently inefficient design due to its sole reliance on the torque converter in normal driving. Exacerbating the situation was the dual stator arrangement, which wasted more power than the simpler three element converters used with other automatic transmissions, such as Chrysler's TorqueFlite. The multiple stators increased turbulence in the converter, even when operating in the coupling phase.

In 1953 Buick redesigned the Dynaflow, calling it the Twin Turbine Dynaflow. The converter now incorporated two turbines but only a single stator, which resulted in better efficiency, especially at highway speeds, as well as a higher level of performance. Buick also incorporated a variable-pitch stator in 1955 for greater flexibility. While these changes improved the transmission's overall performance and efficiency, the Dynaflow still was no match for other designs that utilized three element converters with automatic shifting.

A new version appeared in 1958: the Triple Turbine (Flight Pitch Dynaflow). This unit was similar to the Twin Turbine, but bore some operational differences. A few identifying features: the older Twin Turbine model was fitted with a rear pump, which meant the vehicle could be push-started (considered a desirable feature at the time). Also, the Twin Turbine would allow engagement of low gear up to 40 miles per hour, and had a shift quadrant that read P-N-D-L-R. In contrast, the Triple Turbine unit did not have a rear pump, so it could not be push started, as there was no means to produce line pressure to engage any friction elements. It would, however, allow engagement of low gear up to 45 miles per hour, and had a shift quadrant that read P-R-N-D-G (where "G" stood for "grade retard").

In 1964, the Dynaflow was discontinued in favor of the more efficient Super Turbine 300 two-speed and Super Turbine 400 three-speed transmissions, Super Turbine 400 being Buick's trade name for the Turbo-Hydramatic. One feature of the Dynaflow, the variable pitch torque converter stator, lived on in some versions of the Turbo-Hydramatic (Super Turbine 400) fitted to full-size Buicks, full-size Oldsmobiles and Cadillacs) built from 1965 through 1967.

References in popular culture

• Dynaflow was most famously referred to in an episode of The Honeymooners called "The Deciding Vote" (which first aired on December 10, 1955). In it, Ed Norton (Art Carney) tries to explain the troubles with the vacuum cleaner purchased as a wedding anniversary gift by Ralph Kramden (Jackie Gleason) thus: "The armature sprocket is causing interference; which, in turn, causes the combustion line to interfere with the flow in the Dynaflow." This was a subtle sponsor plug/inside joke, as Buick was the sponsor of the show in the 1955–56 season.
• Ray Charles' second hit record, "It Should Have Been Me" (1954), uses the Dynaflow as a sign of wealth and class in the lyric, "...It should have been me, driving that Dynaflow!" The song was written by Memphis Curtis.
• Malvina Reynolds' song, "The Day the Freeway Froze" (1959), mentions the Dynaflow in the lyric, "And a little VW superbug was winged by a Dynaflow."

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