Some people report successful index shifting with old Suntour ders and Shimano freewheels and shifters,. Maybe 90% of my shifts on the road were fine, and they all worked on the stand. The failed shifts seemed to be due to some stickiness in the mechanism. I think my V-GT needs to be overhauled, but I don't have the skill. I figured there was a significant probability I could take it apart but not put it back together, in which case I'd need a new der anyway, so I just got the new one.