Originally Posted by
FlashBazbo
Thanks for the replies. FBinNY, you caused me to take a closer look at what's actually happening -- at least on the stand. To my surprise, the mis-tracking ISN'T happening when I shift the rear derailleur. It happens, under certain conditions, when I shift the front.
With the chain on the 4th or 5th sprocket (counting from the 11T) and the big ring, if I shift to the little ring, the chain tracks off the idler to the inside (small chainring side). It's off track at initial contact with the idler, but is on the idler within 1/4 of the way around. If I back-pedal even an inch at the crankarm, the chain gets back on track.
The jump from 50 to 34 up front is apparently allowing enough chain slack to let the chain pop off the idler teeth. In that nano-second of slack, the fd is pulling the chain off the idler to the inside. At least that's my theory. Anyone know how to fix it?
I believe it's still an alignment related problem. The wave that moves back when you shift the front dislodges it, but if the chain is coming straight on it shouldn't go over the edge. If you can find pulleys with deeper teeth, they'll engage the chain better and prevent or reduce derailing, but when the chain comes from an angle derailing is still an issue. Note also that they sell thousands upon thousands of these derailleurs and if the pulleys couldn't retain the chain, there would have been a modification.
As I posted earlier, shift to the middle of your cassette, and see if the chain appears to come to the pulley straight on as it should. If not, then you have to align things so it does, with it coming from angles only when the RD is inside or outside of the chainline plane.