Mine isn't jumping from gear to gear, it stays in one gear and jumps. Causes the crank to lurch forward while pedaling. The bike is IN one gear while doing this. I installed another helicomatic from my PH10 peugeot, and it was full speed ahead, no problems.,,,,BD

Cogs are shot I guess. Sorry not trying to hijack. My bike is doing the same thing that's all.