Chrysler’s Fluid Drive was an important step in the evolution of the automatic transmission. Here’s how Chrysler marketed the innovation and a brief look at how it works.
First, we need to do some housekeeping on model years and dates. While this film clip was produced in 1940, the car depicted is a 1941 Dodge, and Fluid Drive first appeared on some 1939 models in the flagship Chrysler division. The feature was then introduced on DeSoto in 1940 and Dodge for 1941. We strive to get the details right.
Anyway, Fluid Drive was an important first step for Chrysler in the evolution from manual to fully automatic transmissions.The mechanism itself was rather simple, as shown in the illustration below: a hydraulic fluid coupling was placed between the engine and an otherwise totally conventional manual clutch and transmission. (Fluid coupling is just a fancy term for a pair of fans or turbines in a bath of fluid, one driving the other, like two opposing water wheels.) Unlike modern torque converters, this fluid coupling produced a simple 1:1 drive ratio without torque multiplication. But it still made driving much easier in a number of ways.
With the engine no longer solidly fixed to the drivetrain and now driving a viscous coupling that was free to slip at low speed, drivers could decelerate to a stop, sit at a traffic light, hold the car on an incline, or drive away, all without depressing the clutch. While the clutch was still required for gear shifting (on these earliest models, anyway) drivers could start out and drive away in second or even third gear—albeit at a more leisurely pace than in low gear, naturally. If you chose, you could drive around all day in third (top) gear, never using the clutch, as long as you weren’t in a hurry.
This poor acceleration performance, and poor efficiency due to slippage, were among the major drawbacks of the original Fluid Drive setup. But developments throughout the industry, led by GM’s Hydra-Matic transmission, quickly addressed these shortcomings with automated shifting and other features, and fully automatic transmissions are now ubiquitous. This 1940 Chrysler film clip provides a brief but clear explanation of Fluid Drive operation and how it makes driving easier. Video below.