Looking for some advice on what to check next. I have a Shimano Di Ultegra 8050 11 speed drive train and have a very annoying chain skip going on, but only when I’m in the 5th cog in back, and only when pedaling under load. Skip happens when using either chain ring in front. On the maintenance stand, there’s no skip unless I start to apply a little brake and power increases. Shifting is normal, and there’s no skip when in any of the other cogs.
I’ve swapped wheels (different cassette). Same skip on just the one cog.
I’ve installed a new chain. Same skip
I’ve swapped rear deraileurs. Same skip.
I’ve installed a new deraileur hanger. Same skip.
I swapped chain rings in front, which required resetting front limits. Same skip. Not sure what else to try. Any suggestions?
I’d try a new cassette. I know you have tried another cassette on another wheel, but what you are describing frequently happens when you change chain on a worn drivetrain: the chain starts skipping on the worn out components.
Just a question: do you use erg mode on your trainer? And if so, are you typically in your 5th cog? If so, that’d explain why you are seeing wear on that particular cog.
I don’t use this bike on the trainer. I live in a very flat area and have a compact in front, so I’m rarely on the big part of the cassette, which is only about 2-months old. I’ll check the quick-link tomorrow. I’m fairly certain that the B-screw adjustment is good, but I’ll double-check it too.
A long shot but worth eliminating is whether your derailleur is slightly bent.
I had something not too dissimilar a few years ago (different cog but similar symptoms) and it was a bent cage that was causing misalignment around the bottom third of the cassette - was OK up the bigger cogs and fairly ok down the very bottom.