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I'm baffled. I installed a new chain, cassette, cables and housing yesterday. On the stand, all is happy and shifting is silky smooth. On the road all seems happy except on the bigger cogs in back (in either ring) where it feels like the chain might skip somewhere under load. More frustratingly, the chain will periodically drop to the inside. On the big ring, it'll drop to the small ring. If I'm in the small ring and biggest cog, the chain will drop without fail within a few pedal revs. When this happens, the chain isn't rubbing on the derailleur though there is definitely the sensation of something slipping. The limit screw is adjusted as far in as possible without the chain rubbing on the derailleur.

I'm struggling to find a cause. I'm using the same wheels and didn't touch the crankset - the chainline didn't change. The chainrings are in good shape, but to eliminate that as a cause, I swapped in an unused pair to no avail.

Any ideas? Thanks

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2  
I suspect the chain length - is the new chain the same length as the old one? –  andy256 May 19 at 1:20
1  
It could simply be a poorly-adjusted cable. But the chain length is also a good suspect. If you haven't changed any of the sprocket sizes the new chain should be the same number of links as the old one. –  Daniel R Hicks May 19 at 2:07
    
Both of the above are good suggestions and thanks for chiming in -- both were things I checked. Turns out that it was an idiot mistake on my part. The special Campy Ultra chain pin wasn't secured 100%. Not sure if the extra 1/10th of millimeter of exposed pin was the problem or if the chain was flexing, but when I went back to tighten it, it snapped into place. –  SDG May 19 at 2:42
    
Yeah, with indexed shifting the chain pins are a critical part of the mix. The cogs have "ramps" on their sides designed to catch the projecting chain pins and "lift" the chain onto a larger cog. If the pin projection is not pretty close to perfect then things can get sucky fast. –  Daniel R Hicks May 19 at 3:15

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