johnlink

I have four cog spacers that I received some time ago with a Shimano Dura Ace cassette. Three of the spacers are 3.45 mm thick while the fourth spacer is 3.53 mm thick. The parts diagram for Shimano's FH-7400 freehub says the spacers for a 6-speed cassette are 3.65 mm thick.

Are these spacers Shimano? Could they be used in a 6-speed Dura Ace cassette?

ThermionicScott 

How thick are the cogs (no peeking at Shimano techdocs)? It's not unusual for Shimano to use spacers of differing thicknesses in a cassette, because real-world indexing works a little better when the smaller cogs are a tiny bit further apart than the biggest cogs.

For example, in the 7-speed cassettes with which I'm most familiar, most of the plastic spacers are 3.1mm, but the one between the 2nd and 3rd smallest cogs is 3.3mm.

johnlink

Why do you ask about the thickness of the cogs? I could measure any of the many cogs I have, but I have no idea which cogs came with the four spacers whose identity I'd like to know.

ThermionicScott 

Rats, I thought they had come as part of the Dura-Ace cassette. If the cogs were 2mm thick, that would point strongly to 6-speed use. I suspect the techdocs you posted call out 3.65mm spacers to go with 1.85mm thick cogs. Either way yields 5.5mm (average) spacing.

Alternately, the spacers could be useful if you wanted to build a cassette using much thinner 10/11-speed cogs but in a wider spacing. If you wanted indexing, you'd still need to throw in a thinner spacer here and there to keep the accumulated error down...

johnlink

All my cogs measure 1.7 mm to 1.85 mm. The spacers came with cogs, but I have no idea which ones. I never considered the possibility that a 6-speed cassette would have cogs of different thickness than a 7-speed cassette, but the Shimano parts diagram leaves open that possibility. Do you know whether a 6-speed cassette requires cogs of different thickness than a 7-speed cassette?



My brother Greg calls me Keeper of the Cogs.

Steel Charlie

I built a 7spd on a 126mm 6spd Dura Ace hub using 8spd (modded) cogs and spacers from a Sram cassette. Shifted just fine.

ThermionicScott 

Nice! Have you seen Sheldon Brown's spacing cribsheet? The freewheel/cassette part is about 1/3 of the way down. You can see that cog thickness isn't always standard between brands -- some brands even used different thicknesses depending on the model! https://www.sheldonbrown.com/cribsheet-spacing.html

So you could use that in cobbling together cassettes for your own use.