If the Shimano Positron AX was the coming together of Shimano’s disastrous Positron technology with its much sneered at AX aerodynamic design. Then this derailleur was Bridgestone and SunTour’s riposte - the coming together of Bridgestone's widely ignored in-derailleur indexing technology, with SunTour's derided Trimec design and hopelessly unreliable ‘Tech’ three pivot technology.
And just like the Positron AX, the result of this marriage of monstrosities was a surprisingly solid and workable derailleur. Albeit one that nobody wanted to buy.
This is a later, black, example with a medium length, openable, pulley cage. It has an 'improved' second pivot seal which is clearly branded SunTour but which I have not seen fitted on a SunTour derailleur
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