Presto-Matic
Encyclopedia
The M6 Presto-Matic was a Chrysler Corporation transmission
produced from 1946-1953. It was a hybrid manual transmission
with a torque converter
or fluid coupling
like an automatic. Although it had just two forward gears, an electric 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
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
-brand cars. DeSoto
called the transmission the Tip-Toe Shift, while Dodge
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
introduced their Hy-Drive
semi-automatic in 1953, but all were replaced by the PowerFlite
automatic in 1954.
This configuration had the effect of providing 4 gear ratios:
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.
Transmission (mechanics)
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...
produced from 1946-1953. It was a hybrid manual transmission
Manual transmission
A manual transmission, also known as a manual gearbox or standard transmission is a type of transmission used in motor vehicle applications...
with a 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...
or fluid coupling
Fluid Drive
Fluid Drive is the trademarked name that Chrysler Corporation assigned to a transmission driveline combination offered from 1939 through 1953 in Chryslers, 1940 through 1953 in Desotos, and from 1941 through 1954 in Dodge models...
like an automatic. Although it had just two forward gears, an electric overdrive
Overdrive (mechanics)
Overdrive is a term used to describe a mechanism that allows an automobile to cruise at sustained speed with reduced engine RPM, leading to better fuel economy, lower noise and lower wear...
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
Fluid Drive is the trademarked name that Chrysler Corporation assigned to a transmission driveline combination offered from 1939 through 1953 in Chryslers, 1940 through 1953 in Desotos, and from 1941 through 1954 in Dodge models...
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
Chrysler
Chrysler Group LLC is a multinational automaker headquartered in Auburn Hills, Michigan, USA. Chrysler was first organized as the Chrysler Corporation in 1925....
-brand cars. DeSoto
DeSoto (automobile)
The DeSoto was a brand of automobile based in the United States, manufactured and marketed by the Chrysler Corporation from 1928 to 1961. The DeSoto logo featured a stylized image of Hernando de Soto...
called the transmission the Tip-Toe Shift, while Dodge
Dodge
Dodge is a United States-based brand of automobiles, minivans, and sport utility vehicles, manufactured and marketed by Chrysler Group LLC in more than 60 different countries and territories worldwide....
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 (automobile)
Plymouth was a marque of automobile based in the United States, produced by the Chrysler Corporation and its successor DaimlerChrysler.-Origins:...
introduced their Hy-Drive
Hy-Drive
The Hy-Drive was a Chrysler Corporation transmission introduced in August 1940 in Chryslers and DeSotos, Dodges in 1949, and Plymouths in 1953. It was a hybrid manual transmission with a torque converter like an automatic. Although Hy-Drive cars had a clutch pedal like a traditional manual...
semi-automatic in 1953, but all were replaced by the PowerFlite
PowerFlite
PowerFlite is a two-speed automatic transmission produced by the Chrysler Corporation and used in their passenger cars from 1954 to 1961. Production began in late 1953; despite the launch of Chrysler's three-speed TorqueFlite automatic in 1956, the simple and durable PowerFlite remained available...
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 6 mph (9.7 km/h), 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 13 mph (20.9 km/h), 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.