Dynaflow was the trademarked name for a type of automatic transmission developed and built by General Motors Buick Motor Division from late 1947 to mid-1963. 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 Assembly plant during World War II. It was also used in the 1951 Le Sabre concept car. History Original version The Dynaflow was an automatic transmission used in various forms in Buick cars by the General Motors Corporation from 1947 until 1963. The transmission 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 3.1:1 torque multiplication, Ref. 1963 Buick Service Manual to accelerate the vehicle. Low gear, obtained via the planetary gearset, could be manually engaged and held up to approximately , improving acceleration. The transmission was incapable of automatic shifting, requiring the driver to move the shift lever from low to drive to cause an upshift. Buicks equipped with the Dynaflow transmissions were unique among American automobiles of the time in that the driver or their passengers would not detect the tell-tale interruption in acceleration that resulted when other automatic transmissions of the time shifted through their gears. Acceleration through a Dynaflow was one smooth (if inefficient and slow) experience. It was because of this slow acceleration that the Dynaflow transmission was nicknamed "Dynaslush." 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. Design rationale During the Dynaflow era, many of Buick's unique engineering features ranked smoothness above most other design and marketing objectives. Dynaflow's non-shifting design was demonstrably smoother than the rough shifting automatics then available. Moreover, Buick's torque tube "live axle" rear suspension design, which incorporated a rigid drive shaft with just one single universal joint ("U-joint") at the front end of the driveshaft, was said to amplify the harshness of contemporary automatic shifting transmissions. Dynaflow's