Originally Posted by
skiingfury
Eventually derailleurs wear out. There are a bunch of pinned connections that are exposed to the same grit that chains are. When these connections get worn, the derailleur gets sloppy. You can tell if you grab the parallelogram and twist, you can feel slop in one that is burned out, a new one will be tight.
You can check the friction in your housings by grabbing the cable and pulling it first from the RD end, and then from the shifter end. No friction = easy pulling.
I'm a newb so I don't have a particularly keen eye for some of this stuff. However, the mechanic did give me the impression that the cassette and derailleur appeared to have very few miles on them. He manipulated the derailleur by hand both on the bike and off.
Cables move beautifully through the housing. Although, I did not test them through the whole system. Maybe that will reveal something, but I'm not hopeful. You'd think a bike mechanic would find something that obvious in about 5 minutes.