The mid-1980s were a disturbing time for Campagnolo. Tullio Campagnolo had died in 1983, SunTour's slant parallelogram derailleur design was clearly established as the dominant derailleur geometry, Shimano's SIS offered consumers reliable indexing and the mountain bike, a alien object that Europeans knew nothing about, was sweeping all before it. Campagnolo's, long successful, strategy of producing ever more refined variations of the 1951 Campagnolo Gran Sport, using ever more exotic materials, was suddenly exposed as being intellectually and even commercially bankrupt.
The obvious response would have been to produce a beautifully polished, obsessively engineered copy of the Shimano Dura-Ace 7400. And that is what Campagnolo belatedly ended up doing in the form of the 1990 Campagnolo Record (RD-01RE). But first Campagnolo had two goes at reinventing the derailleur on their own terms - the 1987 Campagnolo Croce d'Aune and the 1987 Campagnolo Chorus. In some ways these two wildly contrasting experiments were admirable efforts, even heroic failures. But they also remind us that, in the words of Mary Midgley, hubris calls for nemesis, and in one form or another it's going to get it!
The Campagnolo Chorus departed radically from all Campagnolo orthodoxy, and enthusiastically embraced the slant parallelogram - a technology that Campagnolo had been quietly rubbising for two decades. But the Chorus did not only seek to ape SunTour and Shimano - it sought to outdo them at their own game. Its slant parallelogram could be set to one of two levels of slant. Position 'A' gave 5 degrees of slant, and was designed for close ratio sprocket clusters. Position 'B' gave 30 degrees of slant and was for wide ratio clusters. Switching between the two was a reasonably quick and painless process involving loosening and retightening two Allen key bolts.
In this way Campagnolo had cunningly solved a problem that had never existed. Virtually nobody regularly swapped their derailleur between their out-and-out racing bike and their touring bike. They had a close ratio racing derailleur on their close ratio racing bike and a wide ratio touring derailleur on their wide ratio touring bike and never the twain shall meet. Anyway, virtually nobody used Campagnolo derailleurs on a bike with a sprocket larger than 26 teeth - and the short cage Chorus could handle that on setting 'A'.
While solving this non-existent problem Campagnolo had, inevitably created a few very existent ones. The Campagnolo Chorus was heavy, the short cage version was a mere 75g or 46% heavier than the comparable SunTour Cyclone Mark-II. And the Campagnolo Chorus looked all wrong - with its b knuckle and p knuckle distorted by the need for the slant adjusting Allen bolts. Ugly, heavy and pointless - it's a tough act to beat - but for some reason I can't help loving it.
This example of a Campagnolo Chorus is a short caged version that Campagnolo claim will handle a 27 tooth sprocket on setting 'A' (I would go for 26 teeth) and 32 teeth on setting 'B' - although I would again suggest something more modest.
The key to dating a Chorus (C010) is to look at the number of components of the parallelogram module that are, and are not, polished. I think this is an earlier variant, perhaps from 1987 because all the components are polished. The key features are:
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