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The Chrysler-Plymouth-Dodge-DeSoto Hy-Drive automatic transmission

The Hy-Drive transmission became available (in Plymouths, at least) in April, 1953. Advertised as the transmission for those who wanted the ease of automatic driving yet the ability to select their own gears, it was really a stop-gap measure to mark time until the fully automatic Powerflite arrived, around a year later.

Hy-Drive semi-automatic transmission

Basically, the Hy-Drive was Chrysler’s old Fluid Drive, refined. The Fluid Drive used a fluid coupling with a three speed manual transmission and a clutch, to provide clutchless shifting once the car was in motion. The HyDrive replaced the fluid coupling with a modern torque converter, which gave two advantages: drivers didn’t have to lift the accelerator to shift gears, and power transfer was improved so it was practical to use with the Plymouth Six.

The red rubber clutch pedal (imprinted with the words “Hy-Drive”) was only needed for putting the car in gear (or going from Drive to Reverse); you could also start in third, or in first. [added by Allpar:] As a Chrysler Master Tech bulletin told mechanics,

Hy-Drive is a combination of the torque converter and a Plymouth synchro-silent transmission. As the name implies, you can operate the car in high or direct gear under practically all forward speed conditions. You can do all of your stop-and-start traffic driving without shifting gears or using the clutch pedal. ... Hy-Drive is not just the standard transmission with a fluid coupling added. It is a torque converter of the engine-fed type, capable of multiplying the engine torque by more than two and one half times.

Customers apparently liked the system; according to the Standard Catalog of Plymouth, the company was making 3,000 cars a week with Hy-Drive by June 1953.

The system also used a new 8.5 inch high-pressure clutch with a solid hub. A new clutch linkate had less friction for easier operation; the main drive gear teeth were stronger to handle higher torque.

The transmission shared oil with the engine, so owners had to change ten quarters (eleven with filter) — with two drain plugs. On the lighter side, the recommended time and miles between oil changes was doubled; and there was a single filler opening. Some buyers preferred that system. The oil pump remained externally mounted, but added a bypass valve to regulate oil pressure.

Since the buying public was clamoring for automatic transmissions, Plymouth tried to make the Hy-Drive look as “automatic” as possible by placing an indicator quadrant on the steering column, even though the lever still shifted in the normal H-pattern. The one additional advantage of the Hy-Drive was its price: at $145.80, it was much cheaper than any fully automatic unit. Still, the Hy-Drive was seldom mentioned once the new Powerflite automatic became available, and the system was quickly abandoned.

Curtis Redgap added: The Hy-Drive “semi-automatic” transmission was a late-1953-model-year introduction, carried over to 1954. Dealers could not convert a standard car to the “Hy-Drive” because of differences in the engine block, clutch, linkage, gear ratios, speedometer cable, and front floor pans; the Hy-Drive also had a longer, heavier tailshaft, a shorter driveline, larger radiator (due to extra heat from the transmission), and a carburetor dashpot to prevent stalling when the driver quickly lifted off the accelerator. The the main drive pinion clutch hub had sixteen splines, rather than the ten used before; and they added a transmission neutral switch to prevent owners from starting the engine while in gear.

Mike Sealey added: Outside the US, export Dodges and DeSotos based on US Plymouths also used Hy-Drive, which could cause some confusion. Cars with the Hy-Drive would generally have a Plymouth dashboard.

Hemi Andersen added: The driver did all the shifting with “Hy-Drive” exactly the same way the driver shifted a 1948 Dodge with Fluid Drive. “Hy-Drive” meant you could start off in high (3rd) gear. It was quicker than fluid drive, but not by much.

See the Imperial Club’s reprint of a Chrysler bulletin on Hy-Drive.


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