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The FW used a special two-part indicator spindle, with a small spring surrounding the junction of the two parts. The four-speed trigger works normally shifting down through the top three gears, but when you pull it into the bottom gear, it is shifting the two sun pinions, making the secondary sun pinion disengage, and the primary sun pinion engage. You can feel the extra spring tension as you shift into the bottom gear, which may require considerable effort.
The S5 and related models used dual shift controls, with a cable running to each side of the hub's axle.
The original shifters were a pair of top tube levers, designed to look like the shift levers of a derailer bike of the period. These levers were very poorly designed, and never worked very well. The hubs acquired a bad reputation as a result, but that reputation is not entirely deserved. If you replace the original shift levers, these hubs can be quite pleasant to ride, once you get used to their unusual shift pattern.
Shifting the left lever works most smoothly if you keep pedalaing forward (gently) while shifting.
With the S5.1 they reversed the linkage on the left side, using an indicator spindle chain to pull the sun pinions to the left. The S5.2 is similar. The AT5 uses the s5/2 mechanism but with a drum brake, and a shorter planet cage with plunger-type pawls that engage with a radial ratchet on the inner face of the left ball cup.
Here's some official info on upgrading to the S5/2. This is not necessary with the S5 but it is highly recommended with the S5.1, which does not reliably stay in gear (or you could backgrade to an S5).
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Last Updated: by Harriet Fell