Dynaflow
Encyclopedia
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 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, Michigan
assembly plant
during World War II
. It was also used in the 1951 Le Sabre
concept car.
The Dynaflow initially used a five-element torque converter
, with two turbine
s and two stator
s, 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 2.1:1 torque multiplication to accelerate the vehicle. Low gear, obtained via the planetary gearset, could be manually engaged and held up to approximately 40 mph (64.4 km/h), 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. Buicks equipped with the Dynaflow transmissions were unique among American automobiles of the time in that the driver or his/her 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 shifting 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.
In 1953, Buick redesigned the Dynaflow, calling it the Twin Turbine Dynaflow. The converter now incorporated two turbines and a planetary gear set, but only a single stator. The first turbine was linked to the ring gear and the second to the planets, which gave a 2.5:1 torque multiplication which was now partly mechanical. This resulted in better efficiency especially at highway speeds as well as a higher level of performance and no penalty regarding the trademark smoothness. 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)3-speed. This unit was similar to the Twin Turbine, but bore some operational differences, amongst them a variable pitch stator that increased converter's torque multiplication to 3:1. The stator element of the torque converter has two blade positions, controlled by the driver via the accelerator pedal to offer a 'passing gear' and extra response at any speed from heavy throttle application. In normal driving the stator blades are arranged at 'cruise' angle which offers improved efficiency and response at light throttle. Flooring the accelerator pedal changes the angle of the stator vanes hydraulically to 'performance angle' which permits the converter to achieve stall about 1000 rpm higher than in 'cruise' as well as redirecting oil to strike the next-lowest drive turbine which effectively lowers the drive ratio of the transmission and allows engine speed to flare to a speed where output is greatest. 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 mph (64.4 km/h), 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 mph (72.4 km/h), 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, colloquially the "Switch-Pitch", lived on in some versions of the Turbo-Hydramatic (Super Turbine 400) fitted to full-size Buicks, full-size Oldsmobile
s and Cadillac
s built from 1964–1967, as well as the Buick Super Turbine 300 and Oldsmobile Jetaway.
Several thousand 1953 Oldsmobiles were also equipped with Dynaflow.
Buick
Buick is a premium brand of General Motors . Buick models are sold in the United States, Canada, Mexico, China, Taiwan, and Israel, with China being its largest market. Buick holds the distinction as the oldest active American make...
Motor Division from the late 1940s to the mid 1963. The Dynaflow, which was introduced for the 1948 model year only as an option on Roadmaster
Buick Roadmaster
The Roadmaster was an automobile built by the Buick division of General Motors. Roadmasters produced between 1936 and 1958 were built on Buick's longest non-limousine wheelbase and shared their basic structure with senior Oldsmobiles. Between 1946 and 1957 the Roadmaster was Buick's top of the line...
models, received some severe early testing in the M18 Hellcat
M18 Hellcat
The 76 mm Gun Motor Carriage M18 was an American tank destroyer of World War II. The manufacturer, Buick, gave it the nickname "Hellcat" and it was the fastest tracked armored fighting vehicle during the war with a top speed up to 60 mph. Hellcat crews took advantage of the vehicle's...
tank destroyer
Tank destroyer
A tank destroyer is a type of armored fighting vehicle armed with a gun or missile launcher, and is designed specifically to engage enemy armored vehicles...
, which were built in Buick's Flint, Michigan
Flint, Michigan
Flint is a city in the U.S. state of Michigan and is located along the Flint River, northwest of Detroit. The U.S. Census Bureau reports the 2010 population to be placed at 102,434, making Flint the seventh largest city in Michigan. It is the county seat of Genesee County which lies in the...
assembly plant
Factory
A factory or manufacturing plant is an industrial building where laborers manufacture goods or supervise machines processing one product into another. Most modern factories have large warehouses or warehouse-like facilities that contain heavy equipment used for assembly line production...
during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. It was also used in the 1951 Le Sabre
Le Sabre concept car
The General Motors Le Sabre was a 1951 concept car. Possibly the most important show car of the 1950s, it introduced aircraft-inspired design elements such as the wrap-around windshield and tail fins, which became common on automotive designs during the second half of the decade.-History:The Le...
concept car.
The Dynaflow initially used a five-element torque converter
Torque converter
In modern usage, a torque converter is generally a type of hydrodynamic fluid coupling that is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load...
, with two turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
s and two stator
Axial compressor
Axial compressors are rotating, airfoil-based compressors in which the working fluid principally flows parallel to the axis of rotation. This is in contrast with other rotating compressors such as centrifugal, axi-centrifugal and mixed-flow compressors where the air may enter axially but will have...
s, as well as a planetary gearset
Epicyclic gearing
Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...
that provided two forward speeds plus reverse. In normal driving, Dynaflow started in high gear (direct drive), relying on the converter's 2.1:1 torque multiplication to accelerate the vehicle. Low gear, obtained via the planetary gearset, could be manually engaged and held up to approximately 40 mph (64.4 km/h), 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. Buicks equipped with the Dynaflow transmissions were unique among American automobiles of the time in that the driver or his/her 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 shifting 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
TorqueFlite
TorqueFlite is the trademarked name of Chrysler Corporation's automatic transmissions, starting with the three-speed unit introduced late in the 1956 model year as a successor to Chrysler's two-speed PowerFlite...
. 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 and a planetary gear set, but only a single stator. The first turbine was linked to the ring gear and the second to the planets, which gave a 2.5:1 torque multiplication which was now partly mechanical. This resulted in better efficiency especially at highway speeds as well as a higher level of performance and no penalty regarding the trademark smoothness. 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)3-speed. This unit was similar to the Twin Turbine, but bore some operational differences, amongst them a variable pitch stator that increased converter's torque multiplication to 3:1. The stator element of the torque converter has two blade positions, controlled by the driver via the accelerator pedal to offer a 'passing gear' and extra response at any speed from heavy throttle application. In normal driving the stator blades are arranged at 'cruise' angle which offers improved efficiency and response at light throttle. Flooring the accelerator pedal changes the angle of the stator vanes hydraulically to 'performance angle' which permits the converter to achieve stall about 1000 rpm higher than in 'cruise' as well as redirecting oil to strike the next-lowest drive turbine which effectively lowers the drive ratio of the transmission and allows engine speed to flare to a speed where output is greatest. 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 mph (64.4 km/h), 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 mph (72.4 km/h), 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
Super Turbine 300
The Super Turbine 300 was a two-speed automatic transmission built by General Motors. It was used in various Buick, Oldsmobile, and Pontiac models from 1964-1969...
two-speed and Super Turbine 400 three-speed transmissions, Super Turbine 400 being Buick's trade name for the Turbo-Hydramatic
Turbo-Hydramatic
Turbo-Hydramatic is the registered tradename of a family of automatic transmissions developed and produced by General Motors. These transmissions mate a three-element torque converter to a Simpson planetary geartrain, providing three forward speeds plus reverse.The Turbo-Hydramatic series was...
. One feature of the Dynaflow, the variable-pitch torque converter stator, colloquially the "Switch-Pitch", lived on in some versions of the Turbo-Hydramatic (Super Turbine 400) fitted to full-size Buicks, full-size Oldsmobile
Oldsmobile
Oldsmobile was a brand of American automobile produced for most of its existence by General Motors. It was founded by Ransom E. Olds in 1897. In its 107-year history, it produced 35.2 million cars, including at least 14 million built at its Lansing, Michigan factory...
s and Cadillac
Cadillac
Cadillac is an American luxury vehicle marque owned by General Motors . Cadillac vehicles are sold in over 50 countries and territories, but mostly in North America. Cadillac is currently the second oldest American automobile manufacturer behind fellow GM marque Buick and is among the oldest...
s built from 1964–1967, as well as the Buick Super Turbine 300 and Oldsmobile Jetaway.
Cadillac Dynaflow
The early 1950s Cadillacs were normally equipped with Hydramatic transmissions. However in 1953 the General Motors Hydramatic Plant burned to the ground, leaving Cadillac without a source of transmissions. Buick Dynaflow transmissions were hastily adapted to Cadillac mount points, and some 19,000 1953 Model 62 Cadillacs, and some 28,000 Cadillacs of all models, were equipped with Dynaflow transmissions.Several thousand 1953 Oldsmobiles were also equipped with Dynaflow.