Shimano Postive Shift Mechanism (AX Series)
Short Name:Shimano Postive Shift (AX)Year Introduced:1981
Speed Range:7&6spIndexed Component:Rear Derailleur
General Information
With the introduction of the AX series of components, Shimano made their first attempt at an index system aimed at the upper end of the component line.  AX groups were produced from the high end Dura-Ace line all the way down to the Adamas touring group and even a Positron AX  part.  Unlike the SIS shifting system which would be introduced a few year's later, the AX group had its shifting mechanism (called the Positive Shift Mechanism by Shimano) built into the rear derailleur similar to how the Positron systems worked.  Because of this, AX rear derailleurs can not be used in a pure friction mode, however any shifter that has a friction mode can be used with an AX derailleur when paired with a compatible 6 speed freewheel or cassette. 
Shifter Information
Because the AX series of derailleurs has the Positive Shift Mechanism built into the rear derailleur, the AX group shifters were pure friction shifters.  Furthermore, any pure friction shifter capable of pulling the needed amount of cable can be used with a Shimano AX rear derailleur if you wish to set up a Postive Shift bike. 
Derailleur Information
One of the few Shimano derailleurs which will not work in a friction shifting setup, the AX series of derailleurs has the Positive Shift Mechanism built into it.  The Positive Shift Mechanism is a set of small steps which help the derailleur stay aligned on each of the cogs when setup with a six speed freewheel or cassette.  However problems will arise if you try to use this type of derailleur on an Ultra-6 spaced or other count freewheel or cassette. 
Shifting System Component Variations
NameCategoryGearingYear Introduced
6sp Shimano Postive Shift (AX)Rear Derailleurs6sp1981
7sp Shimano Postive Shift (AX)Rear Derailleurs7sp1981
    Notes: Dura-Ace AX only
Component List
Generally in Indexed systems, either the shifting or the derailleur component contains the indexing logic. Here is a list of components currently on which utilize the Shimano Postive Shift Mechanism (AX Series) shifting mechanism.
Component NameModelGroupCompatibility
Rear Derailleurs
Shimano RD-6300, 600 AXRD-6300600 AX6sp Shimano Postive Shift (AX)
Shimano RD-7300, Dura-Ace AXRD-7300Dura-Ace AX7sp Shimano Postive Shift (AX)
Shimano RD-AD10, Adamas AXRD-AD10Adamas AX6sp Shimano Postive Shift (AX)
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