Shimano Positron 400 (DG-300)

Shimano Positron 400 derailleur (DG-300) main image

The Shimano Positron 400 (DG-300) 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.: DG-300 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
Shimano Positron 400 derailleur (DG-300) additional image 01