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Converting a Sturmey-Archer AW Hub Into a Two-speed Fixed Gear

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by Sheldon "Got A Milling Machine?" Brown
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Would you like to ride a fixed gear, but do you need a choice of gears to cope with your local terrain? It would be great if you could find somebody selling a Sturmey-Archer ASC three-speed fixed gear hub, but the chances of that are very slim indeed.

What about converting an existing multi-speed hub into a fixed gear? Is this possible? A reader named Randy Gordon-Gilmore sent me a photocopy of a set of plans that he apparently got from Sturmey-Archer for converting a readily-available AW three-speed into a two-speed fixed gear, giving a direct drive and a 25% reduction gear. All he was able to provide was the drawings reproduced below, no instructions.

Note: I have not tried this modification (yet). I have written a rudimentary explanation below. If this is not clear to you, you don't know enough about Sturmey-Archer hubs to undertake this advanced project. Please don't ask me for more information on this, I don't have any!

For more info on Sturmey-Archer hubs in general, see my Sturmey-Archer page, Jane Thomas's site with the Sturmey-Archer AW shop manual online and my ASC Tech Page. (I cannot find a current link to Jane Thomas's site but the relevant material seems to be available at the Sturmey-Archer Heritage - Product Archive. - HJF 4/2010)

[As described below, a Sturmey-Archer S5-series 5-speed hub can be converted into a three-speed fixed gear using the procedure described here. However, Sturmey-Archer now sells a fixed-gear three-speed hub, so the modification described here is less compelling than it once was -- John Allen]

On the other hand, if you try this yourself, I'd be interested in hearing how it works out for you.

I would expect that there will be a bit of internal backlash, which you'll have to live with unless you feel ambitious enough to make a clutch with wider arms that won't rattle back and forth between the pinion pins.

Note that these parts are made of very hard, tough steel. A standard steel milling cutter may not be adequate for the task.

It is possible that by fabricating non-stepped pinion pins you could reduce the lash a bit. Pins with a large head, like that of a nail, might eliminate it in the direct-drive gear.

[A converted five-speed hub will have no backlash in the direct-drive gear, because the clutch seats directly against lugs on the planet cage. Some early gear rings also had two sets of internal splines, and would reduce backlash in the lower gear(s). --John Allen. ]

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ball cup, planet cage, bar
Figure 1 shows the left hand ball cup (newer splined style, not the older threaded type.)

A groove must be machined in the center ridge of the ball cup to receive the bar shown in figure 3.

Figure 2 shows the planet cage, with a similar groove machined into it.

Figure 3 shows the bar which must be fabricated. This bar will lock the planet cage to the left hand ball cup.

awfixed sketch
The gear ring pawls must be removed. When the clutch is in the "high" position, driving the planet cage directly, you have direct drive. When the clutch is in either the "normal" or "low" gear position, you will get low gear, i.e., 75%.

I would imagine that if this modification were done to a 4- or 5- speed hub, you'd get three speeds: direct and the two lows. This is basically how the ASC works, though not with a standard clutch.

Was this too easy? Try Bruce Ingle's Bichain fixed-free setup!

For a different approach to this, see James Fairbrother's system.

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