Hi Scott, Are you talking about what is commonly called the "grub screw"? An old mid 1950s version is in the lower right under the red bolt, here: <http://www.wooljersey.com/gallery/Torpado_1955_Gran_Sport_52cmBlue/Torp55Gran Sport52LtBlu19?full=1> You can see the side view of it here: <http://www.wooljersey.com/gallery/Torpado_1955_Gran_Sport_52cmBlue/Torp55Gran Sport52LtBlu20?full=1> They seemed to change the design of that piece quite a bit in those years, evidently attempting to hone in it's effectiveness. When the chain tension is released, the pulley cage will spin around until a specific part of it stops on the inside tip of that screw. In more "modern" Campy derailleur versions, like Nuovo and Super Record, the screw is instead attached with the extension pointing outward, and makes contact in a different way. Here is one on a 1973 Nuovo Record: <http://www.wooljersey.com/gallery/Colnago74Super52GreenPanto/Colnago74Super52 Green_Panto14?full=1>
As far as I know, the screw does nothing more than the preload you mentioned, and is not in use ... once in use!
Ciao, Mark Agree Southfield MI USA ~ ~ ~
Date: Fri, 13 Jan 2006 16:54:45 -0800 (PST) From: scott Baxter <rg500g@yahoo.com> Subject: [CR]Pulley Cage Preload on Early Campy Gran Sport
I have an early Campagnolo Gran Sport rear derailleur in hand. No obvious dating, but the body is bronze. Unlike the '74 NR rear derailleur I have, there is no stop on the pulley cage to hold the cage spring under any tension. What I see instead is an interesting screw on the left side of the lower pivot body that seems to go to nowhere.
Is the pulley cage of the Gran Sport rear derailleur by design not tension preloaded, or is that screw a stop screw that seems to break off in every picture I've seen of this derailleur? I have a funny feeling the stop screw breaks off frequently, for part # 99 in the Gran Sport exploded view in Catalog 14 shows a longer screw than is in the derailleur, and its name is "vite regolazione cambio", whatever that means.
Scott Baxter
St. Louis, MO