The repair tag said, "Bike fell over on drive side. Trouble shifting to big ring." The bike was stopped, so it wasn't a serious slamming, sliding crash. There were no major or even minor impact marks.
The front derailleur cable felt a little slack. I thought maybe the cable had simply gone out of adjustment and the bike's fall had been a coincidence. Snugging the cable did not fix the shifting, but it did change the problem enough for me to notice that the front derailleur was not swinging in a smooth arc.
This picture was taken after I noticed that the rivet on which the derailleur cage pivots had backed out about three millimeters. When I tapped it back in, the derailleur then functioned properly. I have no idea how a minor topple could have caused this problem, but there it is: something else to check when normal adjustments aren't bringing the desired results. The rivet could have been backing out already and the minor fall either helped it the rest of the way or had nothing to do with it.
Shown at the center of this shot, the pivot rivet. Derailleur is Shimano 105.
Some older front derailleurs were held together with bolts that can loosen. Check your derailleur and snug these bolts every so often. The term
Marvin bolts comes from the particular repair on which I failed to remember them soon enough.
.JPG)
Some Shimano front derailleurs are held together with bolts that can loosen, leading to erratic front derailleur action, high-siding the chain and eventually falling apart. They had no name until recently. I had not seen a derailleur with Marvin Bolts in a while, so when a customer named Marvin brought a bike in with front derailleur problems, I took care of one of the issues, but forgot the Marvin Bolts. One fell out, and I ended up buying Mr. Marvin a derailleur before never seeing him again because I am obviously a negligent, untrustworthy bastard. Gone he may be, but he has given his name, as Ned Overend did to the Ned Gear and Tinker Juarez did to the Tinker Bolt.
