Cheshire Dave - thanks! that will help a lot!
Richard of WAus. - thanks for the diagrams. No springs hey?? I think I will need to add a couple at either end of the cable. I note that some guru on Gomog recommends a spring at the axle end.
And re the rods - my concern was how tightening them would affect the calipers.. In any case I will experiment on one side to see how it works.
Brownbaker - easier said than done!.. I've pulled everything apart already. And besides, its 40 years old - who's to say that the previous "enthusiast" assembled it correctly in the first place?
Anyhow - thanks everyone - I will check bak here to see if any other good ideas turn up. An will definitely report back with the end result and solution. But don't hold your breath. These things take time.