It was Saturday night around 8:00 PM and we have a race on Sunday morning. I'm in bed with a fever and LOML tells me that she can't shift into the big chain ring.

First step, point out that I setup her bike on Wednesday and asked to to give it a test ride and try out everything. Scratch that, our 28th anniversary is in one week, I've (finally) learned not to say that.

• The obvious first step is to charge the Di2 system - except I do that before every race, it is fully charged.
• Since I was charging it, maybe I accidentally unplugged a wire - nope not it.
• Both the aerobar shifter and the base bar shifter make the rear derailleur move so they are connected.
• I start spinning the crank and shift through the gears. The front der. gives a little twitch at the appropriate time, but doesn't shift the chain.

I start digging through the manual and it mentions that it is ok to force the front der. to move by hand when setting it up. I try to force it to move and the whole front der. swivels on the mount!

It turns out there is a set screw just above the limit screw. This set screw goes through the body of the derailleur and braces the derailleur against the bike frame. This stops the derailleur from pivoting and all is fixed! Either her set screw must have been slowly backing out over the years or the main mounting bolt must have been slowly working loose.

It is not obvious at all from the manual. The lower picture shows a "support screw". The top picture shows a "Backup plate". The backup plate goes on the bike frame. The support screw braces the derailleur against the bike frame by pushing into the backup plate.

The lower picture shows that the mount is curved and the fixing bolt can easily rotate around the mount, hence the need for a support screw.