allenre

Many thanks to all those who have offered help either via this thread or directly by e-mail. Two weeks ago the friend who restored it and I dismantled the lever (actually a real Simplex - I didn't realise they had also produced them without the name branding) and tried various combinations with another Simplex he had in his parts bin. By using the screw from the other one we got it to work fine and determined that the old screw was fractionally too long: the female thread in the brazed-on bush is blind so the screw was stopping short. It was the original item that been on it for decades and had worked fine with the non-original Shimano I put on it 40 years ago but I guess the spring on the Campag was just that bit stronger and, with a certain amount of wear, it overcame the friction. So our solution was to simply add another small washer under the head of the existing screw, just enough to take up the slack, and it works perfectly now - after two weeks' use I have had no more problems.
So again, thanks to you all for your assistance - it's much appreciated.

Aubergine 

Another bump for this old thread. I too am having issues with a Gran Sport rear derailleur that I hope to use on an early 60s Bianchi Record. Looks like I'm off to eBay to find a copy of Glen's manual!

iab

What's the problem?

Aubergine 

Oh, it just does not want to work smoothly. Chain rubs against the cage in some gears, cage does not want to take up chain slack, etc. I am pretty familiar with fettling Nuovo Record rear derailleurs and I saw some pretty obvious differences between them and the GS that are likely related to the issues. I figured that a good manual would give me enough info to figure out how best to set the GS up.

iab

Sounds like a proper cleaning and perhaps winding up the cage spring a notch should fix your ails. I find GS to be quite smooth, just a bit limited on gearing and having the the typical Campagnolo overshift need.

Aubergine 

Cleaning might help, sure. I already wound up the spring, which made a difference but did not fully resolve the issues. Going to see what I can glean from the manual!