Shimano Dura-Ace SIS (7402 2nd style)

Today, we are all aware that the current Shimano Dura-Ace derailleur probably holds the meaning-lite title of 'best derailleur in the world'. Of course every pub in the land will house a self-appointed expert who holds a provocative (and interesting) opinion that they prefer some other, not quite so obvious, model from some other, not quite so obvious, brand - but that is what pub arguments are for.

In 1983, however, things were not quite so straight forward. The 1977 Shimano Dura-Ace (7100) was pleasant, but slightly underwhelming. The 1978 Shimano Dura-Ace EX (7200) was more technically interesting, but by 1983 was kind-of average and very long in the tooth. The 1980 Shimano Dura-Ace AX (7300) was so overly 'interesting' that most consumers of top-end equipment gave it a body-swerve. The Dura-Ace name was struggling and 'best in the world' seemed some distance away.

And then the Shimano Dura-Ace SIS (7400) groupset hit the scene. It had four stand-out attributes, one obvious, and the other three more obscure, but, perhaps, equally important:

Firstly and famously, it introduced the world to SIS, Shimano Index System. The first-ever approach to indexed gearing that worked accurately, reliably, smoothly, subtly and pleasurably.

But also:

SunTour's patent on the slant parallelogram had expired, and so Shimano was, finally, able to deploy the 'best fundamental design in the world'.
Dura-Ace (7400) was manufactured, and finished, to a magnificently high standard. It could seriously claim to be the 'best made derailleur in the world' - a claim that I would happily endorse.
It was styled in a new Shimano design language, which combined a certain minimalism with subtle anodised colours and simple elegant forms. It was a derailleur for adults and, more than that, adults with taste. At the time I would call it 'the best looking derailler in the world'.

Starting in 1984, Shimano rapidly came to dominate the world of high-end components. SIS was, of course the fundamental driver of this - but I suspect that SIS alone wouldn't have worked. If the Sachs-Huret Rival (41.1D) had had reliable indexing it would not have had nearly the same impact - because it was slightly crudely manufactured and, whisper it quietly, plain ugly.

The final oddity was that, in my experience, Shimano Dura-Ace (7400) hardly sold at all. Road bike sales were pretty low in 1984 - and things only got worse and worse over the next decade as the revolutionary new mountain bikes came to completely dominate the market. I found that selling bikes equipped with the eye-wateringly expensive Shimano Dura-Ace SIS (7400) was virtually impossible in the UK. For that market, at that time, they were a totally wrong sort of bike at a totally wrong sort of price point. But as so often in the early history of Shimano Dura-Ace, that misses the point. In the UK, at least, Dura-Ace (7100) and Dura-Ace EX (7200) only sold OK, but established Shimano as a company that was ambitious enough to get involved with the pro-peleton. Dura-Ace AX (7300) sold pretty poorly, but established Shimano as a technology leader. And Dura-Ace SIS (7400), however well or badly it sold, established Shimano as 'the best in the world'.

I suspect that Shimano was more than delighted to rake in the shed-load of mid-range sales that its new reputation generated.

I am aware of 5 different variants of the 7400 series rear deraillleurs. I think that their distinguishing features might be as follows:

The first version (1984) was a 6-speed with model number 7400. At the b-pivot there was no adjustment screw and no external plastic seal. The cable adjuster did NOT have a spring loaded 'click' mechanism. The cable clamp nut took a 6mm allen key. The pulley cage was 47mm centre-to-centre, the outer pulley cage had a pronounced hook at the guide pulley and the pulleys had bronze bearings.
The second version (1985) was also a 6-speed with model number 7400. However it now had an adjustment screw and external seal at the b-pivot. It also had a redesigned 48mm pulley cage plate and ceramic bearings in its 6-speed pulleys.
The third version (1986) was a 7-speed with model number 7401. It was extremely similar to the second version, above, but had 7 speed pulleys. The outer pulley cage plate was labelled '6S-7S SIS'.
The fourth version (1988) was an 8-speed with model number 7402. This was an extensive redesign with changes to nearly every part. The b-pivot had an obtrusive plastic shield, the p-pivot was now concealed, the cable adjuster had a spring loaded click, the cable clamp nut took a 5mm Allen key and there was a dial to change the parallelogram spring tension. The pulleys were 8 speed units with rubber seals. The outer pulley cage plate was labelled 'Integrated 8 SIS' and was round at the tension pulley. The inner pulley cage plate has no 'tab' at the tension pulley.
The fifth version (1988) was also an 8-speed and also sported the model number 7402. This was very similar to the fourth version. However, the outer pulley cage plate has a pronounce bulge at the tension pulley. The inner pulley cage plate now has a 'tab' at the tension pulley.

This is a tidy example of the fifth version described above. Some key features are:

It is clearly labelled with model number 7402.
The b-pivot has an adjustment screw and a prominent external plastic guard.
The p-pivot is concealed.
The inner parallelogram plate has a built-in parallelogram spring tension adjuster.
The cable adjuster has a spring loaded 'click' mechanism.
The cable clamp nut takes a 5mm allen key.
The pulley cage is 48mm centre-to-centre. The outer pulley cage is labelled 'Integrated 8 SIS' and has a bulge at the tension pulley. The inner pulley cage plate has a 'tab' at the tension pulley.
It has 8-speed pulleys with ceramic bearings and flexible rubber seals.

Note that this example was manufactured in 1996 - a full 12 years after the debut of the Shimano Dura-Ace SIS (7400). It's a tribute to the quality of the original basic design that the 7400 series was, arguably, still the 'best derailleur in the world' over a decade after its introduction.