The 1941 M4 Vacamatic transmission by 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....

 was, historically, the first semi-automatic transmission

Semi-automatic transmission

A semi-automatic transmission is an automobile transmission that does not change gears automatically, but rather facilitates manual gear changes by dispensing with the need to press...

 which was marketed by a major manufacturer. It was an attempt to compete against rival's automatic transmission

Automatic transmission

An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...

s, though it still had a clutch

Clutch

A clutch is a mechanical device which provides for the transmission of power from one component to another...

, primarily to change range. In normal driving, the clutch is not used. The transmission itself was a fully synchronised manual type, with four forward gears, one reverse; where the shifting was done 'automatically' by either vacuum cylinders (early, M4), or hydraulic cylinders (late, M6, Presto-Matic

Presto-Matic

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...

). The main difference was the addition of a fluid coupling

Fluid coupling

A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch...

 between engine and clutch, and the shifting mechanism.

Operation

The range selector (looked like a column shift) had three positions: Low, High, and Reverse. Low consisted of what would be first and second gear with an ordinary four speed; High was third and fourth. Reverse was single ratio. Driving one was/is quite different: Upon starting, one would disengage the clutch, then choose a ratio (High for normal driving), and, whilst stopped with foot on the brake, engage the clutch. Pressing the accelerator would move you forward, in third, with the fluid coupling connecting the engine to the transmission. Upon reaching 15–20 mph (24.1–32.2 km/h), the accelerator is lifted, a 'clunk' would ensue (the automatic shift), and you would continue in fourth gear. Low range was quite similar, but much slower speeds. It is possible to start in Low, allow the shift, then move the range selector to High, using the clutch, and continue in High. This allowed somewhat faster acceleration, but was quite clumsy. Kickdown for passing was possible through electrical connections made by flooring the accelerator, though only in one range (i.e.: fourth to third).

Commentary

Never a performance transmission, it was nevertheless fine behind the six or eight cylinder flathead engine

Flathead engine

A flathead engine is an internal combustion engine with valves placed in the engine block beside the piston, instead of in the cylinder head, as in an overhead valve engine...

 but once the V8 Hemi engine

Hemi engine

A Hemi engine is an internal combustion engine in which the roof of each cylinder's combustion chambers is of hemispherical form.- History :...

was introduced, the shortcomings of such a slow-shifting transmission were magnified greatly. Over the years, though, this transmission has acquired a reputation for absolute reliability.