Okay, so I have this new used bike. Almost everything working great. Made some cockpit adjustments, took a spacer out of the fork, replaced a valve core. That's about it. Except one crazy thing that I can't figure out. Before I take it for professional attention, maybe one of YOU can give it some professional attention.
SRAM XO 11-speed rear derailleur. Problem description in next paragraph. Here are things I've looked into already: Played with the B-screw, setting it to spec (jockey wheel 12-16mm below the big cog, per the SRAM install manual) and back to where it was when I got it (more like 8 - 10mm). No difference. Limit screws are fine. Cable action is fine (not sticky). Chain looks pretty new. No significant stretch by ruler test. Not sure about cogset - can't be more than a year old, and by the looks of the rest of the bike, seems unlikely to have a ton of miles on it. Not sure if a bent hanger or cage would cause the problem (below). Don't have a device to check.
Here's the problem: As the derailleur climbs the cogs from smallest to largest, the cable tension appears to grow increasingly too tight. I.e., the further you climb the cogs, the more one click of the shifter causes the derailleur to want to overshoot the target cog and start moving toward the next one, causing noise, yadda yadda. Basically it's a problem on the top 3 or 4 cogs. If I reduce cable tension to the point that it shifts okay on the largest cogs, it is way too loose to shift properly on the smallest cogs. E.g., one index "click" at the shifter won't even come close to moving the chain from the smallest cog to the next-smallest one. The indexing is off somehow.
I have been using a stopgap measure to keep me riding while I futz with the issue. I'll describe it here only as a diagnostic: Tighten the cable one cog's worth. When I do this it basically works fine on the largest 7 or 8 cogs. Since I spend the vast majority of my time in that range it's getting me by, but it's not right and it bugs me.
Ideas?
SRAM XO 11-speed rear derailleur. Problem description in next paragraph. Here are things I've looked into already: Played with the B-screw, setting it to spec (jockey wheel 12-16mm below the big cog, per the SRAM install manual) and back to where it was when I got it (more like 8 - 10mm). No difference. Limit screws are fine. Cable action is fine (not sticky). Chain looks pretty new. No significant stretch by ruler test. Not sure about cogset - can't be more than a year old, and by the looks of the rest of the bike, seems unlikely to have a ton of miles on it. Not sure if a bent hanger or cage would cause the problem (below). Don't have a device to check.
Here's the problem: As the derailleur climbs the cogs from smallest to largest, the cable tension appears to grow increasingly too tight. I.e., the further you climb the cogs, the more one click of the shifter causes the derailleur to want to overshoot the target cog and start moving toward the next one, causing noise, yadda yadda. Basically it's a problem on the top 3 or 4 cogs. If I reduce cable tension to the point that it shifts okay on the largest cogs, it is way too loose to shift properly on the smallest cogs. E.g., one index "click" at the shifter won't even come close to moving the chain from the smallest cog to the next-smallest one. The indexing is off somehow.
I have been using a stopgap measure to keep me riding while I futz with the issue. I'll describe it here only as a diagnostic: Tighten the cable one cog's worth. When I do this it basically works fine on the largest 7 or 8 cogs. Since I spend the vast majority of my time in that range it's getting me by, but it's not right and it bugs me.
Ideas?