Originally Posted by
Bob Gabele
As I have returned both of them to Campy, I do not have the opportunity to get a picture. In both cases, the band broke when shifting up to the big chainring and the derailleur got sucked in between the seatube and the small chainring. It really tore up the cage in both cases. I live in Florida and the terrain was totally flat. I was not hammering but instead coming out of my warmup and doing, in each case, an easy shift to the big ring. I have six bikes (all Campy ranging from Super Record to Record to Ergo Record) and have been riding for over 20 years and have never seen anything like this occur.
I was originally thinking overtorquing may have been the cause but I'm now leaning the other way and I'm thinking your derailler clamp is undertorqued. Given the position of the cable clamp on the derailler, if the clamp was loose, the front of the derailler would get rotated into the chainrings if the derailler slipped. When you shift into the big ring, the shift cable gets put under a lot of tension which could cause this.
Given the (assumed) fragility of carbon fiber (both on the clamp of the derailler and your seat tube) it could be possible that your LBS is going too safe with the torque they are applying. This in turn is causing the derailler to slip. When it slips, it's getting pulled into the chainrings and it's the chainrings getting caught in the derailler that breaks the clamp. When you tell Campy that the clamp breaking is the root cause of the problem, they may well be right that the only way that clamp on it's own would break is in a crash. Perhaps if they were looking at the problem from the standpoint of the clamp slipping as the root cause, they might be more willing to work with you. It could be possible that Campy's low end torque spec is not enough to hold the clamp in place. If that's the case, they owe you two deraillers. If the LBS is undertorquing from their fear of cracking something, they need to get over it and fix your bike properly.