Sheldon Brown states in his web site that the 1983 Suntour Symmetric levers had a serious flaw. He said that the movement of the rear lever would cause the front lever to tighten, thereby pushing the front cage closer to the big chainwheel and thereby eliminating chain rub. He then stated that the flaw was that by constantly going up and down in the rear, it would eventually cause the front derailleur to progess too far and thereby causing a new problem. I finally obtained one of these nice old shifters. I don't have a single bike that doesn't have side braze ons for the levers, so I haven't verified what he said ...BUT from my bench top view of things it does look like the levers do not have this flaw. Instead of rotating the front lever around, the internal cam pushes the lever forward in the housing. As you move the rear lever back and forth it appears that the other lever perfectly returns to the exact same position as before. I think I have this right and it is just possible that Sheldon is in error.
Offered in humble questioning. Both Suntour and Sheldon are my heros.... Garth Libre in Miami Fl USA