My 2 year old Shimano BD-7800 rear deraileur equpped bike with about 8000 miles on it abruptly began developing shifting problems. When the barrel is adjusted just enough to cause a shift from the smallest cog to the next, it won't reliably shift up to larger cogs. When adjusted to shift reliably to larger cogs, it balks at shifting to a smaller one. When adjusted to shift reliably to a smaller cog, it won't shift relibaly to a larger one. There does not appear to be slop or binding in the shift cable, and I've replaced the chain though it wasn't yet "stretched" enough to warrant replacement - no improvement.
The derailleur does not appear to be binding either. The smallest movement of the shift lever either way results in an equally small movement of the derailleur.
At this point, I can only surmise that maybe there is too much float in the jockey wheel. I know there is supposed to be some with Shimano index systems, but I don't know how much.
Any other ideas, or tips on the jockey wheel?