Originally Posted by
Crankycrank
Have you checked the cable for any type of damage? If it's got a kink or broken strand/strands it may prevent the derailleur from moving all the way over but won't affect the other gears. Pretty sure you can just buy an 11t cog for 105 but if not Ultegra or DA will work and not too expensive. Compared to your larger cogs 11t don't last long if used a lot.
The cable looks fine... it's internal cable routing so I can't say 100%, but it looks fine on the parts I can see.
And I'm fairly sure it's releasing enough of the cable tension to sit in the correct spot because when adjusting the H limit screw I am able to get the chain to move too far outward (as in it would drop off the cog, if I went that far) and I can get it to move inward to where it will jump to the next cog. But when the H limit screw is set in the "best" spot, it's still not anywhere near as quiet as the rest of the cogs.
Yea... I'm starting to think maybe it might be a worn cog. I do have 2 other Ultegra 11-28's on my other 2 race wheelsets. I could pull an 11t off one of those and try it and see if that resolves the issue. The bike came with this 105 and I just use it on my training wheelset.