Technical FAQ: Autoshifting
Originally published: Aug. 18, 2009
Another solution: One other solution to Dan’s “auto shift” problem:
I had the same thing happen to me on my Rivendell Rambouillet with indexed downtube shifters. Turns out, grit had accumulated under the bottom bracket and was causing friction between the cables and the bottom bracket.
When I stood on hills, the extra torque makes the bottom bracket sway back and forth.
All is OK if the cable was able to slide as normal, but with the fact that I was in first gear so the derailleur couldn’t move to the left, the friction made it so that the cable eventually caught enough that it pulled the derailleur just far enough to the right that it would drop a gear.
Very frustrating, but after brushing the bottom bracket clean and squirting some oil on it, all was better.