Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Mentioned: 9 Post(s)
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It could be that the chain is first moving toward center since it's unguided when back pedaling, then is no longer on the sprocker under which the RD is positioned. This is very common at either end of the cassette.
The other possibility is that the RD is riding a bit high and there's not enough clearance between the pulley and sprocket.
This is easy to check. Shift to the problem gear, and look at the pulley, chain and sprocket. There should be a gap between the pulley and sprocket with free chain between them. (compare to the other bike). If you suspect that's the problem, tighter the "B" screw at the back of the upper RD body to push it down and away from the cassette, and establish the necessary clearance.
An ounce of diagnosis is worth a pound of cure.
“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin
“One accurate measurement is worth a thousand expert opinions”
- Adm Grace Murray Hopper - USN
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