Forum members might remember some trouble I had with my X-RF5 hub a while back involving a rattling noise whilst free wheeling/coasting. The problem was cured after I took my hub apart, though I never discovered any specific cause.
Recently I've been riding a Brompton with a 3 speed SA hub and the same problem exists only this time I've serviced the hub and it's not been cured. Searching the web has revealed that some people seem to think that this issue is endemic to SA hubs.
For instance here:
"Compared with the 12 year old T5, the new T6 felt more free running and stiffer - less flex in the handlebar stem. The 3-speed Sachs hub seemed to make a louder ticking sound both in drive and coasting, but of course without the rattling that accompanies coasting with an old Sturmey-Archer hub."
This thread appears to be about exactly the same problem, though it's clear from the responses that the cause isn't identified:
"has anyone cured an AW rattle ? I took it apart last night and put
it back together and though the cones are now more snug on the drive
side the rattle hasn't changed. it never rattles under power, just coasting
and when hitting bumps"
If every SA hub rattled when coasting then (besides the fact that no-one would use them) it would be stated as a known issue on forums. But it seems that only some hubs suffer from it and adjustment of some kind affects it.
So I'm wondering, is it a specific part of the hub that's rattling or are there several parts that are loose enough to rattle (when not under pedaling load)?
What's different from one hub to another such that some rattle and others don't?
Could it be to do with the quarter or half-turn loosening off of the bearing cone? I.e. is that difference of tension enough to affect the way the internals mesh together?
I'm trying to picture the situation in my head (not easy):
One potential culprit would be the driver vibrating against the planet pinions. In 3rd gear (on a 3-speed) the driver is engaging the pinions pins when pedaling, so when you stop pedaling the driver is next to the pins and free to rattle against them.
If you're in gear 1 or 2 there's more likely to be space between driver and pinions as they wouldn't have been meshed during pedaling. In those gears the clutch drives the gear ring, so when not under pedaling load those two parts would be free to vibrate against each other. . . presumably.
At this point my head is exploding.
The driver could be rattling against the clutch if there's a bit of play in the fit.
I guess one has to establish how the rattle changes depending on the gear one's in to get a clearer picture of what parts are causing it. But having done that what's the solution? Perhaps it's merely a question of making sure there's loads of grease in that drive-area of the hub (if grease is the solution then older oil-based hubs would always rattle).
Could the exact tightness of the drive-side bearing cone (i.e. half-turn/quarter-turn) make any difference?
I've forgotten the driver-type configuration on my X-RF5, I know it's quite different to an AW. . . yet a similar rattling problem arose.