fadedglory

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?

neil

Is it possible there's kink in the cable somewhere? Indexed shifting can be very sensitive to cable kinks, since it's like a spring in the middle of the cable, and means the amount of movement will be different depending on cable tension. It's generally too small of a difference to measure, but would prevent proper adjustment for all gears.

operator

You really have to eliminate about a page of things before concluding it's the jockey wheel. At any rate, take a new derailleur and compare the amount of play - that will give you an answer immediately. Excess play in the upper pulley will cause shifting problems. Does the wheel teeth *look* significantly worn? How much use has the derailleur gone through? Those will give you some clues.

brucewiley

I got bit with shifting problems a while back and it turned out to be dried Gatorade goop under the BB in the cable guide. It doesn't wash off easily!

Shimagnolo

Same thing happened to me but it was my homebrew maltodextrin/fructose mix.
I couldn't believe how firmly that cable was cemented into the guide!

fadedglory

BB guide is OK, derailleur hanger and derailleur are tight. There is the very slightest amount of play in the wheel tension arm pivot (the bolt is tight though), again I don't know what is normal. No kinks in the cable either. I'm going to have to find a bike with a fairly new derailleur and compare tolerances.

Panthers007

When was the last time to replaced your cables? After 8,000 miles - I'd say they are over-due. And new cable-housing with the cables. This will allow you to examine the entire length of the cable - from the shifter to the derailleurs themselves. And rule that possible cause out.