John Foster

Hello all

I recently purchased a used Scott CR1 with retro fitted Ultegra RD-6870 shifting. Initially all was well with the bike. Then I decided to up my game on cleaning and servicing my bikes so I built my own service stand. When I got the bike up to eye level, I noticed that the rear derailleur was quite loose. There was visible thread (+/- 3/16") between the derailleur and the chainstay. The set screw that positions the derailleur angle was barely on the ledge it rests against and the specialized fastening bolt was less than half way through the chainstay. I could wiggle the derailleur by hand.. I tightened up the fastener assuming that it had been working loose over time, and also assuming the previous owner had been doing adjustments to compensate.

As soon as I did this everything went bad. When I shifted down to the largest cog the chain would get thrown over the inside of the cassette ( the high/low limit set screws had never been adjusted) and I had to use up just about all my right adjustment on the Di2 trim to get the chain to go onto the smallest cog. I can't get rid of missed shifts or multiple shifts now, I think I have worked through every position possible on the derailleur adjustment. On an eleven speed cassette, there should be 10 shifts from one edge of the cassette to the other. Currently it only takes 6/7 shifts to go from smallest to largest, and 8/9 shifts to go from largest to smallest. A clean shift going one direction on the cassette can be a total disaster going the other way. I have watched a lot of online videos about Di2 adjusting, and think I am doing it right.

Here are my questions

Can Di2 be confused? Is it always in the gear that it thinks it is in?
Everything looks good on the bike, could there be damage that does not show?
Is there a potential compatibility problem between the bike and the component? Did the previous owner have the derailleur set out from the frame to make it work? I am a tinker and am all about hack fixes, but why would he not have got a longer fastener and used spacers?
Is this a case for a professional in a shop that does a lot of Di2 work?

Koyote

I'm wondering if the derailleur hanger is out-of-alignment, and the previous owner had made some compensating adjustments. Or, given the multiple shifts you are getting, perhaps your cassette is worn out. Perhaps both.

Seems like you should take it to a shop. Tell them to check (and fix, if necessary) the hanger alignment first.

While they've got the bike, ask them to update the Di2 software, if an update is available. (Though an old OS would not cause your problems.)

BHG6

I agree with Koyote - sounds like a bent derailleur hanger to me as well. There is normally a very slight gap between the derailleur and the hanger but it should still feel solidly mounted to the hanger.

You'll need a hanger adjustment tool to see it though - probably $100 or so and if you ride a lot, you'll need one eventually anyway. Otherwise, it's a trip to the LBS

John Foster

Thank guys

I will turn it over to the pros. I know all the shops are way behind on service this year, fortunately I kept my old reliable, will still be able to get to work.