Shimano Dura-Ace EX (7200 3rd style) derailleur

Having chosen to take the fight to Campagnolo with the Shimano Dura-Ace (7100), Shimano then (justifiably) decided that Campagnolo’s soft underbelly was technology.

The Dura-Ace EX (7200) introduced Shimano’s EX concept which I understood as being a design optimised for the (then radical) idea of using 6 speeds, particularly with the new Freehubs. It has virtually no inner pulley cage plate and a clever ‘Hatch-Plate Mechanism’ that allows the chain to be removed and inserted into the derailleur without tools. Campagnolo’s Nuovo Record was famously bad at handling 6 speed cogs (with the change into top gear, just before a sprint for the line, requiring faith, hope and charity) - and Shimano aimed to do the job properly - using science rather than religion.

Despite all of this, I found the Dura-Ace EX (7200) slightly unconvincing in its claims to be the ultimate derailleur. It lacked the clean, lightweight, minimalism of the Dura-Ace (7100), the true, bomb-proof, design of the Campagnolo Nuovo Record and the slant parallelogram of the SunTour Cyclone. Any dropped parallelogram gear will wear more quickly than the traditional Campagnolo design - because it loads the parallelogram pivots with some torsion. Any design without a slant parallelogram will not change as well as a SunTour. Any derailleur with two springs working against each other will be prone to one of the springs suffering exhaustion and going out of balance with the other.

I once heard a story of how Enzo Ferrari came upon Audi testing the original Quattro at Imola. The Audi engineers showed the great man their five cylinder engine, their weird engine bay layout with the in-line block almost in front of the front wheels and their radical four-wheel-drive system. Enzo Ferrari asked if he could take it for a test ride - and the Audi engineers agreed. Afterwards they eagerly asked him what he thought, and he is supposed to have replied that he could not congratulate them enough on the brilliant way that they had solved all the problems that they had caused for themselves. There is something of the Audi Quattro about the Dura-Ace EX (7200).

The Dura-Ace EX (7200) went through 4 generations:

The first version (1978) had a Hatch Plate with a squarish inner plate. It had pins in two parallelogram pivots to keep the cable adjuster and cable clamp bolt aligned. And it had no spoke protector at the tension pulley. and it had basic, one-part, plastic seals around the heads of the main b-pivot and p-pivot Allen bolts.
For the second version (1980) the Hatch Plate was improved with a curvaceous inner plate.
The third version (1982) introduced a spoke protector at the tension pulley.
The fourth version (1983) saw the removal of the two pins in the parallelogram pivots to keep the cable adjuster and cable clamp bolt aligned. Also the seals around the heads of the main b-pivot and p-pivot Allen bolts were improved to be a two-part design.

This is a thoroughly used example of the third version described above. Some key features are:

The parallelogram has pins in two pivots to keep the cable adjuster and cable clamp bolt aligned.
The Hatch-Plate on the pulley cage has a curvaceous inner plate.
The partial inner cage plate at the tension pulley has a built in plastic spoke protector.
The seals around the heads of the main b-pivot and p-pivot Allen bolts are a basic, one-part, plastic design.

Note that there is a crack in the mount that holds the cable clamp bolt. This is a touch surprising, because this is a steel component. However, this is not the first time that I have seen a crack in this position on a Shimano Dura-Ace EX (7200).