(German Wikipedia)
Torpedo Freilaufnabe (freewheel hub) is the brand name of a bicycle rear wheel hub from the manufacturer Fichtel & Sachs with freewheel and coaster brake. The special feature of this hub is the cylindrical rollers, which are pressed radially against the hub housing when riding to transmit the drive force.
The Torpedo freewheel hub has been installed in bicycles since the beginning of the 20th century and had by far the largest market share in Germany for many years. It was developed by the employed designer Johann Modler after eight years of development with numerous modifications. The inventor left F&S due to non-participation and founded the still existing Aschaffenburger Maschinenfabrik Johann Modler GmbH.
Fichtel & Sachs had been building the torpedo freewheel hub since 1903. Thanks to the roller freewheel, the popularity of the torpedo freewheel hub was mainly due to its smooth running and largely low-maintenance operation. The Torpedo freehub was the standard in better utility bicycles for decades. The highest production figures were achieved between 1960 and 1980. It has since been largely replaced by imported products and derailleur gears.
A little later, Fichtel & Sachs also built freewheel hubs with gear hubs, initially under the Wanderer license DRP 131486.
Even if freewheel hubs are very low-maintenance, they do not function indefinitely. Environmental influences (heat, moisture, etc.) and the intentional or unintentional addition of foreign substances can cause the lubricants in the bearings and gearbox parts to resinify. This leads to shifting failure (in the case of manual transmissions) and, in the case of heavier loads, to the destruction of the transmission or freewheel hubs.
In the case of freewheel hubs, the back-pedal brake sometimes fails or jams, with the result that the chain drive is suddenly pulled along. Hub maintenance should therefore be carried out at certain intervals. This involves completely cleaning the gearbox and applying new bearing and brake grease. During final assembly, it is important to adjust the bearing play - if a gearbox is operated with bearing play that is too tight or too loose, the bearing surfaces can crack, which can lead to bearing or axle breakage.
Most damage to manual transmissions is caused by broken gear or spring parts that are held in the lubricant. As soon as these get between the gears, the planetary gearbox is destroyed.
