The Shimano Positron 400 (DG300) was a racy little number, with a dropped parallelogram, an aluminium rear knuckle and a short 46mm pulley cage. It had something of the look of the Shimano 600 (or rather its steel intensive brother - the Shimano 400).

However the geometry was noticeably different, with a distinct backwards slant on the rear knuckle - so that the rear sprung pivot is behind the parallelogram - the weight was even more distinctively different - and then there was that despicable piano wire...

Close, Colonel, but no cigar.

• Derailleur brands: Shimano
• Categories: Shimano - Positron indexing insanity
• Country: Japan
• Date of introduction: 1977?
• Date of this example: unknown (no two letter date code)
• Model no.: DG300 or P240
• Weight: 329g including hanger plate
• Maximum cog: 28 teeth (Sutherlands 6th edition)
• Total capacity: 28 teeth (Sutherlands 6th edition)
• Pulley centre to centre: 46mm
• Index compatibility: 5 speed
• Chain width: 3/32”
• Logic: operated by piano-wire cable with no ‘normal’ position
• B pivot: sprung
• P pivot: sprung
• Materials: largely steel, with an aluminium b-knuckle