Fichtel & Sachs Hubs

Sachs hubs are German, and very high quality. They used to be called Fichtel and Sachs back in the 1960's. I have no idea what happened to Fichtel. In 1997, which is much too recent for our interest, Sachs was taken over by the American components company, SRAM. Inside the hubs, the parts are beautifully machined and look very precise compared to Sturmey hubs. Even so, they can develop problems due to unfortunate details in the design of the pawls. Sachs "Torpedo" 3 speeds from the 1970's have legendary durability. A cyclist who has been travelling the world by bicycle for the last 40 years has made his entire journey using the same Torpedo 3 speed. If you look to the top of any page on this site you'll see the exploded diagram of this hub.

The Fichtel & Sachs Torpedo Duomatic

torpedo duomatic siteThis two speed hub is no longer made, and in fact there have been no new F&S Duomatics since around 1980, despite the huge interest that surrounds this brilliant concept. The hub is neat and relatively small and light, but within the shiny corrugated shell there lurks a coaster brake and two-speed mechanism that, get this, can be changed by simply rotating the pedals backwards a quarter turn. This means that no cables are needed going to the rear of the bike. Sun Race Sturmey Archer have introduced a similar hub in recent years, the S2C, and from what I've read, there were teething troubles. Complaints don't seem to be recorded after 2012 and the S2C is still made. But it has a hard act to follow as the original Duomatic was so durable and reliable.

small duomaticThe Duomatic was developed especially for small-wheeled folding bikes and for this reason they are almost always found with 28 holes in the shell. (Small wheels = less spokes). Dr. Moulton was an advocate of the Duomatic, using it first on Stowaway model, then on the Mini Automatic and finally on the spaceframe AM2. The latter bike came out in 1983, after the Duomatic had been deleted.

The Duomatic Exploded

An important thing to know about the Duomatic is that there are two different models, often called the old Duomatic and the new Duomatic. Interestingly, they are almost identical outside but really quite different inside. The old Duomatic has a thicker axle that has flats machined along the length, meaning that you can grip the axle in a vice. This is a great aid to stripping down the hub. Taking apart the two hubs, you will find that the gear changing mechanisms are different. Inside the new Duomatic, there is a brown plastic ring that is able to revolve when the pedals are rotated backwards. It clicks the high gear in and out in a similar way to a biro. As for the old Duomatic, there is no plastic ring and one of the parts has two sets of pawls (ratchet bits) pointing in opposite directions.

Here is the exploded diagram of the old Duomatic:

duomatic old thumbAll of the parts to the left of the hub shell are components of the coaster brake. Most of the parts to the right are the two speed gear, although nos. 17 and 22 are also used to apply the brake. So as you see, the gear itself has an amazingly low number of parts. And these are all extremely durable components that will literally last a lifetime. An obvious difference between any Sachs hub and a Sturmey-Archer design is the way in which the pawls are sprung. Pawls are the little clicking parts that engage with corresponding steps in the hub shell, part number 26. Sturmeys use very delicate steel wire that looks frail. I have made replacements from the thinnest electric guitar string. German engineers must have thought this could be improved upon, and replaced the little springs with a fat wire ring around both pawls. However, in practice we find that Sturmey pawls, rotating on a shiny axle, are extremely reliable whereas Sachs pawls can stick. This is usually the fault on a Duomatic if it ever does stop working. Cleaning, lubricating and perhaps bending the wire ring slightly restores the pawl function.

The first design of Duomatic as described above was made from 1964 to 1970. This means that all of the 2 speed Moulton Stowaways, Automatics and Mini Automatics will have the old hub design. I have therefore decided to begin with a photo stripdown of the older design because there is less information about it on the web. The second design was made from 1970 to 1980. Here is an exploded diagram:

torpedo duomatic new thumbThe brown plastic ring is part number 20; the pawl spring is part number 15. Curiously, the first Duomatic was lubricated by a combination of grease in the ball bearings and the brake, and also by oil in the actual gear components. Oil could be replenished regularly through an oil port, and by regularly I mean every 2 years. Only grease was used in the later design, and from my experience the same type of grey/black grease throughout the hub. That is why you will not find an oil port on the later hub shell.