better try yourself to repair your bike in the future. I had terrible torment for 2 years with 4 bikeshops from my town (the last one was for retro bikes). When I bought my bike I had the same problem with jumping. All mechanics told me that the derailleur (Campagnolo 980) was old and worn out, the rings were also changed. Three months later, the derailleur broke and I gave it for repair. I put the cheapest derailleur while I'm waiting for the old one. A week ago, two years later, the mechanic called me and told me that there was no way to get it. Well, I looked for another. After a long search, I decided to put on modern and stop the pains. I bought a new one, I know it's ugly, but I've already spent a lot of money for that bicycle. Putting it, it jumps again. With the cheap I didnt have a problem. I was just thinking of calling the store and screaming, because they were sending me a broken derailleur and I found that the hanger, which is very small, seemed hideous. I took the plumbing wrench (about 50 cm animal), put the old derailleur and pushed. ITS PERFECT! Like everything else I've decided to fix myself. The problem with mechanics is that they do it for money. We can't avoid this fact. They cant day and night repair just one bicycle, as I do with my own bike, just because I put my soul in it. Greetings! And yeah i got modern tourney, and i dont care anymore.