With groundbreaking innovations and robust technology for practical use - with this range, ZF products gave the young company access to the world of motorcars and commercial vehicles in the 1920s. Following years of recession, armaments production, and the destruction of many of its locations during the war, 1945 saw ZF resume its former product success as well as its image as an innovative company.
The phrase "Roaring Twenties" was not only coined from the sounds of Charleston and Jazz, the roars of the engine were also an influencing factor: Particularly the time after hyperinflation in Germany was a period of growth for the young automotive industry. Companies such as Maybach, BMW, and many others who, like ZF, started out in the aircraft industry, then caused a surge towards motorization on land. The original rule that a chauffeur had to be employed to drive the car and manage its complex operation soon no longer applied: Wealthy citizens who could afford a car increasingly wanted to get behind the wheel themselves.
When in 1921 the Soden transmission was exhibited at the Berlin Motor Show by the the "Zahnradfabrik Friedrichshafen" just six years after the company was founded, this preselector transmission without shift lever was years ahead of its time. The driver selected the desired gear on a gear selector located on the dashboard or on the steering wheel. Upon actuation of the clutch, the gear was automatically engaged in the transmission by spring mechanism. The transmission was fitted with a multidisk starting clutch; the gears were especially hardened and ground. In the years to come, a total of 75 automotive manufacturers fitted their vehicles with the Soden transmission - an impressive figure yet an indication of the weakness of the former market economy. Although the taxicabs of Vienna in the 1920s and all trucks of a brewery (Böhmsches Brauhaus) were fitted with the Soden transmission, it did not sell in large volumes as many of the manufacturers only built small numbers of vehicles.
Control of quantities and costs with the "ZF standard transmission"
The market structure continued to be a cause for concern for ZF over the years to come as the many small manufacturers also had extremely special requirements regarding how their transmissions should be built. This stood in stark contrast to ZF's more industrial approach: ZF designers developed a "standard transmission" for passenger cars and trucks, pursuing the idea of a modular transmission construction kit as is still in use today. A basic and robust transmission that ZF could deliver with three or four gears in various models and five sizes of housings for both passenger cars and commercial vehicles could satisfy all demands and installation requirements. The advantage being that ZF could manufacture the same transmission for several customers which promised large quantities. This factor, alongside a basic design, secured cost advantages and in turn presented the market with a convincing argument. A virtuous circle that gave ZF an enormous economic success: The company sold a total of 300 000 models of the standard transmission until well into the 1930s.
Silent and comfortable
Besides focusing on market demands, ZF continued to be noted for its technical innovations. In response to increasing engine outputs and speeds, ZF launched the "Aphon low noise transmission" (meaning "without noise" in Ancient Greek). Aphon transmissions were the first transmissions featuring helical-cut gears to offer a revolutionary new running smoothness and meant that the familiar high-pitched sound of a transmission running at full speed disappeared from the road and city soundscape forever. The "Aphon" low noise transmission became the next economic success and was quickly followed by another innovative breakthrough: In 1930, ZF introduced synchronizers for the most frequently shifted gears – when the driver wanted to shift gear, he no longer had to double declutch by first engaging the transmission in neutral and then matching the speeds of the transmission input shafts. ZF supported this trend with a further invention, the first freewheel. The result was in 1934 the launch of the first multi-synchronizer transmission – a fully-synchronized low-cost transmission for volume production cars with smooth running characteristics in all gears.
Diversification and new start
In which other areas can ZF technology still be used? This was the question this young company asked itself when it made its successful transition from the aircraft to the automotive industry. Constant repositioning has since then become a trademark feature of the company. There have been several times in the past when ZF designers and the corporate management have looked around for alternative operating ranges and new sales markets. In the 1930s, before this question was answered by the Nazi state in Germany and the production of transmissions for military vehicles predominated at all ZF production locations, ZF made its breakthrough into steering technology and – with the launch of its first tractor transmission in 1937 – into the world of agricultural machinery. Two production lines that ZF managed to resume after the end of the Second World War. In the immediate post-war years after 1945, the production of tractor transmissions became an important mainstay for the company – one of the main customers was the former tractor manufacturer Porsche with its factory in the nearby town of Manzell at Lake Constance.
The 1950s saw ZF resume its pre-war spirit of innovation in the production of passenger cars and truck transmissions. Alongside the manufacturing of robust constant-mesh transmissions for trucks, the company also experimented with the Media transmission, a semi-automatic solution to make gear-shifting and clutching operations far easier for the driver. This development work later became the nucleus for the development of the multi-ratio transmission for passenger cars and commercial vehicles.