SunTour Superbe Pro GT (5800? 1984 version) derailleur

At the time I remember being deeply, deeply, disappointed by this derailleur. The bike shop where I worked made something of a speciality of high-end British-style touring bikes. We loved the SunTour Cyclone Mark-II GT and sold it in bucket-loads. We could have sold a ton of an ultimate, up-market SunTour derailleur that used the Cyclone GT's geometry - but added the Superbe's signature features - lusciously polished anodising, removable parallelogram pivot pins, sealed bearing pulley wheels and stainless steel and aluminium small parts... But what we got was the SunTour Superbe GT (5800) and its Pro sibling.

The problems started with the slant of the parallelogram. This was shallow - ideal for a close-ratio racing cluster, but useless for touring purposes. These huge derailleurs, with a total capacity of 38 teeth could only accept a maximum rear sprocket of 25 teeth. Bizarre. Then there was the missed opportunity of the pulley wheels - which were perfectly good, but totally mundane, plastic items - no improvement on those on the Cyclone GT. Next up were the strange, massive, thin guage pulley cage plates (one of which was steel!) which made a tinny noise as you changed gear. And finally there was the weight - the Superbe GTs were around 40g heavier than the Cyclone GT. You can accept a sliver of a weight penalty for superior construction (the short cage Superbe was, after all, 10g heavier than the short cage Cyclone) but 40g and you're having a laugh.

These derailleurs do not appear in many catalogues, so it is difficult to be sure of the various versions. Even the model numbers are obscure. I have a SunTour Service Manual from 1985 that lists the SunTour Superbe GT (5800), but does not give a number for the Superbe Pro GT. Elsewhere I have seen the SunTour Superbe Pro GT referred to as also having the part number 5800 - which seems a touch odd.

I rather vaguely think the following:

The only differences between the Superbe GT and the Superbe Pro GT are the writing and anodising on the outer parallelogram plate.
Early GT models from 1983 have the slimmer b-knuckle and 19mm b-pivot bolt. From 1984 they have the chubbier b-knuckle and 22mm b-pivot bolt.
Earlier models (1983) have slightly less huge pulley cage plates. Later models (possibly from 1984) have slightly more enormous pulley cage plates. The centre to centre distance is the same in both cases, it is the extravagance of the chain pusher plates that increases.
Early models (1983) have plastic pulley wheels that are identical to each other. Later models (possibly from 1984) also have plastic pulley wheels but there are specific guide and tension pulleys with different tooth profiles.
Hideki Sasaki says that the very earliest models had steel b-pivot bolts. He also suggests that there were versions that had a cable adjuster. I have never seen either of these in Europe.
The contemporary racing Superbes were offered in a range of interesting colours. In contrast, all the GT models that I have ever seen have been silver.

I believe that this is an unused example of a 1984 version of the SunTour Superbe Pro GT. It has the following attributes:

It has a chubby b-knuckle and a 22mm long b-pivot bolt.
The plastic seal between the p-knuckle and the outer pulley cage plate is relatively thick and has a protruding part to cover the trap for the end of the p-pivot spring.
The pulley cage plates are the larger of the two types used on the GT versions of this generation of Superbes.
The pulley wheels are SunTour's later standard plastic units. There are specific guide and tension pulleys with different tooth profiles.