Replacing a Positron II with a modern gear shift I was tinkering on an old Enik Roadbike (see here: Convert old road bike to comfortable commuter). Most of the parts were still working fine, but the Positron II was not in a good shape, so I bought a "new" one from ebay. This did work reasonably good for about a year now, but the bike was not moved too much during that time. Now again I'm having problems with the replaced Positron II. 

While I was searching for a way to fix it, I found a few posts online where people were mentioning that the Positron is not a good derailleur and they woud recommand to replace it - but no recommendation of what a good replacement for the Positron II would be.


Is it possible to replace the Positron II with a more modern, reliable gaer shift? 
What would be a good replacement for a reasonable price? 
And how much efford would that be?
Positron doesn't have return spring but instead uses single wire for pushing and pulling. That means you have to replace the cable and shift lever, too.

The photo shows that the bike has claw mount derailleur. The best bet is to get a cheap claw mount derailleur and non-indexed shiter.