russmcb

I've got bizzare rear shifting problems with my Ultegra 10 from 2006 (6600?) shifter/derailleur. After a lot of messing around trying to get the rear shifting dialed in properly I realized the following: the distance that the derailleur travels with each shift is a tiny bit farther than the distance between any two cogs. So, I can get the derailleur to shift properly over one end of the casette but by the time it gets to the other side it's skipping a gear. I can tune the derailleur to one end of the casette or the other but there's no way I can get it indexed properly across the whole casette. I set the limit screws first and I tried different approaches, including adjusting the indexing for one of the two middle cogs--no luck.

I finally gave up and just stuck the casette spacer between the 7th and 8th cog (which looks horrible). But now when I adjust the derailleur for, say, the 1st or 2nd (easiest or second easiest) cogs it shifts perfectly across the whole casette. Weird, no? I'm tempted to leave my hack job in place because it works great, but I'm still curious about what's going on.

I'm running a compact 50/36 in the front and a 11,12,13,15,17,19,21,23,25,27 in the back. I've got a short rear derailleur. I assume that my derailleur can handle a maximu sprocket size of 27. The needed derailleur capacity is (50-36) + (27-11) = 30. Maybe my derailleur can only handle a capacity of 29--???

Any ideas appreciated.

Thanks,
russ