Chrysler’s Fluid Drive was an important step in the evolution of the automatic transmission. Here’s how Chrysler marketed the innovation and a quick, clear look at how it works.
First, 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 coupled to the drivetrain and now driving a viscous coupling that was free to slip at low speed, drivers could roll 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—but 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. When the old timers reminisce about the turtle-like acceleration of Fluid Drive, that’s what they’re talking about.
This poor performance and 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. Here’s how it actually worked on the road. Video below.
Thx MCG. Being just about the only transmission I HAVEN’T shifted in my life, I always wondered how that worked. My 1950 Packard had the “Ultramatic”, the 2nd fully automatic transmission, and it was a slug,,,but it was fully automatic. Even though this Fluid Drive was revolutionary, I think many were hesitant, this still had a clutch pedal. It seemed like this was more of a convenience for people who already knew how to drive a manual. Wasn’t until the HydraMatic came out. That changed everything.
Howard, HydraMatic was introduced in 1940 model Oldsmobile in 1939, roughly the same time of Fluid Drive. GM and RIO also started the Automatic safety transmission which is like the Fluid Drive back in 1934. Transmissions with fluid couplings are more efficient at higher coupling speeds than a Torque converter where their efficiency falls off due to the multiplier getting in the way . HydraMatic used four speeds to compensate for the loss by getting the transmissions coupling to spool up, and they also used split torque in the transmission so that the coupling was only taking a percentage of the engine power while the other part of the split torque was in mechanical connection delivering more power from the engine to the rear wheels and giving better mileage. Roto Hydramatic even further developed this concept adding a small stator to the fluid coupling and multiplying first gear and two ranges until RPM built up so that the coupling operated in the normal fashion, second gear or 3rd ranged was accomplished by draining the coupling entirely for full mechanical connection and for third gear or fourth range the fluid coupling fills and we are in one to one and in split torque where 40% of engine power is going through the coupling and 60% is in mechanical connection. HydraMatic is the most efficient automatic’s made until the lock up torque converter. Packard, with the help of it’s engineer John DeLorean developed this for UltraMatic, but unfortunately the transmission only had two forward speeds and was not versatile enough coming up through the gears just like DynaFlow and Powerglide and later Turboglide which relied on the multiplication of the converter to get the car moving and then efficiency would drop off because the multiplying unit or units would get in the way. Oldsmobile even touted that the HydraMatic was more efficient that stick shift transmissions.
Having used the Hydramatic in Aussie Holdens from 61 on they were power robbing slugs on the 138ci grey motor. On the later 179 with a LOT more power they were ok, just. Though they ‘flared’ when changing and still soaked up the power. Plus they had the damper plate that did not have a very long life and on occasion stopped driving when all the springs fell out! But on the open road they were ok when the lock up happened.
Chevvy however was using the powerslide with fast and faster gears. Strong and never very efficient or economical either.
I have never had anything to do with those fluid drives, though Torque flites were a good way above the offerings from GM and Ford in that period of early 60s.
Do not know what transmission ( model #) you are talking about. Flaring on any Hydramatic is a TV adjustment problem not the trans itself unless it’s worn out.
I still vividly recall my Dad’s 1950 DeSoto “Deluxe” four door sedan! The rear seat folded down for us kids to sleep on long trips, and the clutch was used to shift from “Drive” to “Reverse!” Then there was the night we all got stuck in some little town in Ohio with our 1953 Lincoln, as the transmission had given up on us. The “automatic transmission” in our new Jeep has nine (9) speeds!
Drove a 42 Chrysler in the 50s. Used clutch to shift from forward to reverse but otherwise simply let up on accelerator and trans shifted to higher gears. Very smooth.