After writing Vintage Cyclross Bike (VCB) VCB 1.0 and VCB 2.0 , I need to craete a VCB 1.5. Though I'm keeping the seat and brakes, I reverting back to the Gran Sport rear derailleur. Below you will see how I managed to tweak a Gran Sport derailleur (rated at 26T cog)to work flawlessly with a 28T cog.
One of the most frustrating thing about the Nuovo Record era was the 26T limit of the Nuovo Record and Gran Sport rear derailleurs. There were even attempts of varying success at grafting on a larger cage to facilitate using larger cogs. This not to say there were not other work arounds; shortening the chain and moving the wheel forward in the dropouts met with varying levels of success. This is the result of a standard Nuovo Gran Sport on a 28T cassette with out attempting any mitigating factors. You will see it will shift, but not so one would trust it would work. In the follow-up video "Camapgnolo Nuovo Gran Sport w/ 28T cog" Part 2 we will find a more elegant solution.
In Camapgnolo Nuovo Gran Sport w/ 28T cog Part 1, we saw that a Nuovo Gran Sport rear derailleur does not handle a 28T very well; this is not a surprise as they along with the Nuovo Record are only rated at 26T. In this video I have grafted a Super Record backplate (also called the outside plate)on my Gran Sport derailleur. The Super Record rear derailleur of the Nuovo record era, was nothing more than Nuovo Record derailleur with some visual changes and titanium pivot bolts. However, the change to a 28T cog was accomplished by simply raising the lower pivot on the back plate, thus lowering the jockey pulley. As you can see this new arrangement not only works well with a 28T, but could probably accommodate an even larger cog.
Okay, this may make little sense as it is probably easier to get a Super Record derailleur than to find just the backplate. However, you may not want to use a Super Record on a particular build, but want a better working Gran Sport derailleur. The Super Record backplate also solves the Achilles heal of the Gran Sport rear derailleur. Both the Nuovo Record and Super Record have a 1/4" thick aluminum back plate; the Gran Sport has a ridiculously thin steel back plate. The aluminum back plate is certainly stronger also about 2 to 3 times as stiff. The result is the Gran Sport back plate can bend with just a moderate amount of pressure, say leaning it against something. This leads to the fact that I have 1) never seen a Gran Sport rear derailleur that does not have a back plate that needs some truing and 2) It is very common for Gran Sport rear derailleurs to get bent so badly that they get sucked into the rear wheel. I learned this with the first Gran Sport derailleur I bought; yes it got sucked. I also found another at an LBS that was all bent up in the same manner.
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