Originally Posted by
miamijim
Where do they say that 77XX shifters will work with a 74XX derailleur? If I'm reading the charts right they say the 9-speed levers are NOT compatible with pre '97 Dura-Ace (7400).
From SB: And I think there's someting worng with the CTC table. How can a Shimano 8-speed lever not be compatible with and old Dura Ace derailleur but a 9 speed lever is? There's something wrong with the chart. I think its that all the Shimano levers listed are non-DA levers.
Its easy.
Pre '97: Everything interchanges with everything except Dura Ace. Dura Ace must be paired with Dura Ace.
Not quite right, even according to
Shimano. The ctc chart explains it all, but it can be a little mystifying to read. Here's how to do it.
Lets look at the Shimano mechanism table.
Non-74xxDA Shimano RD have a
1.7 actuation ratio. The 74xx have
1.9 actuation ratio.
Next: look at the cable pull/shift column. Shimano 8 (ex-DA) pulls
2.8mm/shift, Shimano 9 (all) pull
2.5mm/shift.
If you take a Shimano 8s (ex-DA) shifter and a non-DA RD, you get
2.8x 1.7 = 4.76mm c-c cog spacing (it's actually 4.8 so the cable pull/shift stated is rounded off slightly from the 2.8 shown)
If you mix a 9s STI and a 74xx RD, you get
2.5x 1.9= 4.75mm (also 4.8), which is Shimano 8s spacing
And the same formula means that a 10s STI will shift a 74xx RD in 9s mode (4.35mm cog spacing) [1.9x2.3=4.37]
So it's not luck, nor is it voodoo, it's just math.