Originally Posted by
RoadTire
First question is why did you replace the RD? The circumstances might help identify the root cause.
Originally Posted by
FBinNY
1- start with a square hanger, which puts the RD parallel with the wheel. You can check by shifting to any gear where the cage is fairly vertical, then look from behind the bike and compare it to a straightedge placed against the wheel.
My guess is you have a wonky derailleur hanger. If your derailleur isn't aligned to the same plane as your rear wheel, it'll never index properly.
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