Shimano DG-300, Positron 400
Main Photo
Category:  Rear Derailleurs
Name:  Shimano DG-300, Positron 400
Brand:  Shimano
Primary Group:  Positron
Model:  DG-300
Years:  1980's - ?
Country:  Japan
Weight:  329 grams (Spec),
Weight given on Disraeli Gears
Added By: Walkman-man on 03/20/15
Updated By: Walkman-man on 03/20/15
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Shimano DG-300, Positron 400Shimano DG-300, Positron 400
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Outer Plate MarkingsInner Plate Markings
MaterialSteelDesign CategoryDrop Parallelogram
Attachment Bolt SizeClawCable Attachment Bolt Size9mm Wrench
Shifting SystemsPositronCable AdjusterYes
Cage LengthShortMax Cog Size28
Max Chain Wrap  
General Information
Looks like this was one of the later Positron models made, seeing as this is one of the few existing with the dropped parrelelogram design. And this is most likely the immediate successor to the non dropped Positron DG-200 model, seeing as the DG-300 has replicated this mech's styling exactly- although having changed things technically a good deal. On the 'net, Disraeli Gears has some useful comments on this, and also points out how this design was even different to its dropped parrelelogram same period Shimano brothers, that (if the dropped parrelelogram change had only recently come on the scene, as I assume) must have been going through a period of considerable design flux at that time. Date code is GD.
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Additional Resources
Resources:Reference & ChartsCatalogs
Component Groups
Primary Group NameBrandQuick InfoBrowse Group Components
PositronShimano1975 - , RecreationView 10 Components
Brand Information(click to expand)

Shimano Model Number Prefix List:

BB Bottom Bracket BL Brake Lever BR BRake
CB Coaster Brake CJ Cassette Joint CN ChaiN
CP Chain Protecto CR Chain Ring CS Cassette Sprockets
DF chain DeFlector DH Dynamo Hub FC Front Crank
FD Front Derailleur FE Fork Ends FH FreeHub
FS Front Suspension HB HuB HD HanDle bar
HP Head Parts (Head Set) HS Handle Stem IF Inter-3 Freehub
LP LamP MF Multi Freewheel PD PeDal
RD Rear Derailleur RH Rollerbrake Hub RM RiM
RR ReflectoRs RS Rear Suspension SB Shift Brake lever (Nexus, ?)
SC Speed Calculator (cycle computer) SF Single Freewheel Freilaufritzel SG Speed chanGe hub
SH SHoes SL Shift Lever Schalthebel SM SMall parts
SP Seat Post SQ Seat Quick release SS Single Sprocket
TL TooL WH WHeel ST Shift Brake Lever (STI, Rapid Fire, etc)
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