jPrichard10 

Hi all,

I've got a broken spring in a first gen Suntour Cyclone rear derailleur. I've got a source for a replacement spring, but I can't for the life of me figure out how to remove the old spring. In the tech manual, it looks like the "cap" screws off for easy spring extraction:
Suntour Cyclone & Cyclone GT Cages c.1980

Any idea how this is done?

Velocivixen

You need that obsolete tool in the second photo on your link. There are probably people who have worked out something else out that works.

Andrew R Stewart 

IIRC the chrome cap on the outer end of the cage pivot bolt is a separate piece from the rest of the bolt, which is the portion that the spring wraps around/slides over. You need to hold the pivot bolt and simply use a hex wrench to loosen the cap. When it comes off you'll see the outer end of the spring and that it's tang fits into one of the cuts across the bolt's end. Padded jaws, a collet of the right size or even a drill chuck might be used to hold the bolt. Andy.

Since you'll be replacing the spring anyway you might be able to grind it away and be then able to grab the bolt under where the spring had been. Also the tool is likely used to tighten the bolt onto the cage. It's end had two dogs which look to fit in the bolt heads crossing cuts, therefore needing the cap to be removed before the tool can be used. A big screwdriver will sub for the tool. I did a number of these ders back in the day.