Following their experiences supplying the Shimano Crane to a European pro racing team Shimano became convinced that the key to success at pro level was a combination of sophistication and durability. They wanted to combine the indestructability of the Campagnolo Nuovo Record with (whisper it quietly) the sophistication of the SunTour Cyclone and Superbe.
The result was this derailleur - the Shimano Dura-Ace (7100). It is a heady cocktail of 3mm and 6mm allen bolts (even the adjustment screws) and cold forged aluminium. The pulley wheels have two part bronze bushings, like Campagnolo, and, in a curious echo of the Sanko-sha Procyon, it incorporated a ‘Synchro-Line Mechanism’ whereby the cable outer stop and the cable clamp bolts were kept aligned by a pin through the each of the relevant pivots.
I am rather fond of this rear mech, it is sophisticated without being complex and, to this day, it remains Shimano’s only real attempt at making a truly lightweight derailleur. This black example is particularly stylish.