pwa wrote:It bothers me too. I wonder if it has something to do with many non-Shimano freehubs not being self-contained, sealed units that come away from the rest of the hub with all their innards still sealed as Shimano units do. Perhaps they are noisier because they operate in a resonating chamber. I think they may also act directly on the main hub shell, which may amplify noise.
Sounds like the best explanation I have heard. Of course Shimano has the freehub patent which stops others from using the same construction. It must be expiring soon though.
as Mick says it Is a contribution but it is not the whole story by any means. For example freewheel mechanisms which use a single 'loop' return spring on the pawls are almost invariably a lot quieter than those which use individual springs, even though other aspects of the design might be near-identical.
BTW one of the faults that can occur (especially with freehub pawls which are set on a small diameter) is that the pawls may not engage at the same time; one-pawl drive is to be avoided, because it always ends in tears.
Freewheel mechanism designers often seem overly keen to make the pickup lash as a small as possible. Some riders (eg in trials) are very keen on this, but for others it ought
to be less important. If you find yourself wanting more than ~18T or so (which is typical for shimano freehubs) on the road, I suggest a treatment which includes riding around on an old SA hub with both clutch lash and a 10T (dog ring) freewheel for a while; that'll cure you!
As a bonus you will learn to engage drive smoothly, rather than smashing the pawls into drive, and this will give any freewheel mechanism you subsequently use an easier life.
Anyway, it doesn't seem to matter how you try and reduce lash in a conventional freewheel mechanism, it always seems to increase the chances of one-pawl drive. For example sometimes there can be four pawls in two pairs such that an opposed pair is engaged and drives, whilst the other pair is not loaded. The dog ring appears to the user to have twice as many teeth as it actually has, because the other pair are ready to engage when the first pair are half-way between teeth. Engagement speed-wise there is some point but engagement quality-wise this arrangement is arguably pointless vs having twice as many teeth in the dog ring, because you have still doubled the chances of one-pawl drive.
If you turn a wheel very slowly forwards, you can often hear the freewheel pawls clicking back. If the mechanism is 'perfect' all the pawls will click back simultaneously, with a single 'click-k' sound. However if the mechanism is imperfect you will hear individual clicks, not just one, and worse yet if the dog ring is even slightly eccentric the interval between clicks will vary depending on the wheel position, and the mechanism is basically a 'no-hoper'.
A recent realisation is that whilst the 'loop' type pawl spring is never as forceful as individual springs, it may also decrease the chances of one-pawl drive due to another effect. This other effect is that usually, the pawls are not all sprung effectively unless all the pawls on the same spring are free to move; if one pawl tip is not yet free to spring back, this reduces the force on the other pawls too, so (provided they remain seated properly) they are presumably that bit more likely to work in unison.