In the pantheon of Shimano’s aero derailleurs, the Shimano adamas AX dwells in that no-man’s-land between prestige and utility - the very no-man’s-land where profits should be maximised. It has just enough aluminium and shiny Allen bolts to catch the beady eye of the eager punter, and just enough pressed steel to put a smile on the face of each and every one of Shimano’s shareholders. What a pity it didn’t sell.

The steel front knuckle and pulley cage look very like those of the budget Shimano Positron AX, the aluminium b-knuckle is a nod towards the enthusiast’s Shimano 600 AX (6300).

Like all of the 'AX' aero derailleurs, the Shimano adamas AX went through several generations within an alarmingly short period. I know of three:

• The first generation (1981?) had a steel outer paralelogram plate with a plastic 'hatch' covering the centring screw. It is indexed, with a stepped ramp behind the b-knuckle. The selector screw for 5, 6 or 7 speeds is mounted on a separate plate attached to the b-knuckle (as on the first style of Shimano 600 AX).
• Very soon after (also in 1981?) came the second iteration. This is largely identical, except that the selector screw for 5, 6 or 7 speeds has been incorporated into the body of the b-knuckle.
• Finally (in 1982?) the derailleur was extensively redesigned, with an aluminium outer parallelogram plate and with no indexing. The ramp behind the b-knuckle is smooth and step-free.

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This, used but very usable, example is a Shimano adamas AX II. Note the aluminium outer parallelogram plate and smooth, non-indexed ramp behind the b-knuckle.

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• Derailleur brands: Shimano
• Categories: Shimano - the turbulent AX story
• Country: Japan
• Date of introduction: 1982
• Date of this example: 1983 (two letter date code HD)
• Model no.: AD12
• Weight: 257g
• Maximum cog: 28 teeth (Shimano)
• Total capacity: 28 teeth (Shimano)
• Pulley centre to centre: 58mm
• Index compatibility: friction
• Chain width: 3/32”
• Logic: top normal
• B pivot: unsprung
• P pivot: sprung
• Materials: largely steel, with an aluminium b-knuckle and outer parallelogram plate

Ref. 603