The M6 Presto-Matic was a

Chrysler Corporation Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automoti ...

semi-automatic transmission A semi-automatic transmission is a "theoretical" multiple-speed transmission where part of its operation is automated (typically the actuation of the clutch), but the driver's input would be required to launch the vehicle from a standstill and to ...

produced from 1946–1953. It was a special

manual transmission A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom, and the United States), or stick shift (in the United States), is a multi-speed motor vehicle transmission (mechanics), transmission ...

with a

fluid coupling A fluid coupling or hydraulic coupling is a hydrodynamic or 'hydrokinetic' device used to transmit rotating mechanical power.

. Although it had just two forward gears, an electric

overdrive Overdrive may refer to: Organizations * OverDrive, Inc., a digital distributor of entertainment media ** OverDrive Media Console, a media player developed by OverDrive, Inc. * Overdrive PC, a subsidiary of Velocity Micro Technology * Overdrive ...

unit was attached and useful in either gear for a total of four forward speeds. The driver would use the clutch pedal any time when selecting low, high, or reverse gear. Once underway, the accelerator could be eased and the car would engage the overdrive. With the

Fluid Drive Fluid Drive is the trademarked name that Chrysler Corporation assigned to a transmission driveline combination which replaced the flywheel with a hydraulic coupling and performed the same function as a modern torque converter, only without torq ...

coupling, the car could be brought to a halt in gear without releasing the clutch and would creep like an automatic. The Presto-Matic name was only used on

Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automoti ...

-brand cars. DeSoto called the transmission the Tip-Toe Shift, while

Dodge Dodge is an American brand of automobiles and a division of Stellantis, based in Auburn Hills, Michigan. Dodge vehicles have historically included performance cars, and for much of its existence Dodge was Chrysler's mid-priced brand above P ...

used Gyro-Matic, Fluid-Matic, Fluidtorque, or Gyro-Torque. Chrysler and DeSoto sold the unit from 1946–1953, while Dodge did not introduce it until 1948.

Plymouth Plymouth () is a port city and unitary authority in South West England. It is located on the south coast of Devon, approximately south-west of Exeter and south-west of London. It is bordered by Cornwall to the west and south-west. Plymouth ...

introduced their ''

Hy-Drive The Hy-Drive was a Chrysler Corporation semi-automatic transmission introduced in 1953 in US-market Plymouths. It was a hybrid manual transmission equipped with a torque converter, like an automatic. Although ''Hy-Drive'' cars had a clutch pedal ...

'' semi-automatic in 1953, but all were replaced by the ''

PowerFlite PowerFlite is a two-speed automatic transmission engineered and produced by the Chrysler Corporation and used in their passenger cars from 1954 to 1961. Production began in late 1953 and the simple and durable PowerFlite remained available on P ...

'' hydraulic automatic in 1954.

Operation

Attached to the transmission was an “underdrive” with a reduction gear of 1.75/1. The shift lever was column-mounted and had three positions: Low (in the “2nd” position of a conventional 3-speed manual unit), High (in the “3rd” position), and Reverse (same as the 3-speed). The clutch had to be depressed every time the gear shift lever was moved. When the lever was put in Low, the car started in “underdrive” low; when the vehicle reached a minimum speed of , the driver lifted his foot off the accelerator, the underdrive unit would kick out and the car would be in Low. Similarly, with the lever in High position, the car would start in underdrive high, and at any speed above , the driver would lift his foot and the car would “shift” into direct drive. This configuration had the effect of providing 4 gear ratios: *Underdrive Low, 3.57/1, *Low 2.04/1, *Underdrive High, 1.75/1, *High, 1/1. In order for the unit to work without gear clashing, it contained a freewheeling device (in Underdrive, Low and High), and the Owner’s manual cautioned drivers not to use “1st or 3rd” gear when descending hills because there was no engine compression braking in those free-wheeling ranges. Generally, most drivers started an M6 car in High and accomplished the shift to direct drive somewhere between 13 and 25 MPH by releasing the accelerator pedal and waiting for the “clunk” that signaled the disengagement of the underdrive. An M6 car would automatically shift from High down to underdrive high when car speed dropped below approximately 11 MPH.

Operation

References

See also