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Unequal spacing of cogs in 7-speed Dura Ace cassette

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Unequal spacing of cogs in 7-speed Dura Ace cassette

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Old 07-11-18, 05:31 AM
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johnlink
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Unequal spacing of cogs in 7-speed Dura Ace cassette

On my Dura Ace 7-speed cassette, I noticed that the width of the (1st position) threaded cog with spacer is slightly less than the width of the (2nd position) cog with spacer which is equal to the width of a spacer plus a regular cog. So the spacing between the first and second cogs is slightly less than the spacing between each of the other adjacent pairs of cogs. Why might that be so?
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Old 07-11-18, 07:48 AM
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'Need to know which Dura Ace free hub are you working with.

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Old 07-11-18, 07:50 AM
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Are you perhaps missing a thin spacer from behind the threaded cog? A slight difference is not too relevant, since the first cog's position is set by the low limit and you set the indexing (if used) to make the shifting line up anyway.
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Old 07-11-18, 10:40 AM
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Is it causing you problems shifting? If not, don't worry. I think that on some they do space them slightly different to optimize shifting.
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Old 07-11-18, 12:19 PM
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Originally Posted by johnlink View Post
On my Dura Ace 7-speed cassette, I noticed that the width of the (1st position) threaded cog with spacer is slightly less than the width of the (2nd position) cog with spacer which is equal to the width of a spacer plus a regular cog. So the spacing between the first and second cogs is slightly less than the spacing between each of the other adjacent pairs of cogs. Why might that be so?
I recommend you look at your bike much more closely -- use high magnification and precision measurements. Then you'll have a valid context for the variability already observed, rather than some random internet guessing. Meanwhile, I'm going for a ride.
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Old 07-11-18, 03:36 PM
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Originally Posted by AnkleWork View Post
I recommend you look at your bike much more closely -- use high magnification and precision measurements. Then you'll have a valid context for the variability already observed, rather than some random internet guessing. Meanwhile, I'm going for a ride.
I'll be ordering a digital calipers and will post precise measurements regarding the spacing once it arrives.
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Old 07-11-18, 03:38 PM
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Originally Posted by dean51 View Post
'need to know which dura ace free hub are you working with.

Dean
It's FH-7400.
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Old 07-11-18, 03:41 PM
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Originally Posted by dsbrantjr View Post
Are you perhaps missing a thin spacer from behind the threaded cog? A slight difference is not too relevant, since the first cog's position is set by the low limit and you set the indexing (if used) to make the shifting line up anyway.
There's no thin spacer between the threaded cog and the second cog.
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Old 07-11-18, 05:11 PM
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I just measured a 7-speed cassette for a 7400 Dura Ace freehub.....that was conveniently removed from the hub for another issue. I have good quality digital calipers and here is what I found:

1st position cog with integral spacer (threads on to the 32 mm portion of the hub body) is 4.98 mm.

2nd position cog with integral spacer (splined on inside diameter) is 5.16 mm.

The cog plus separate spacer combination for the 3rd through 7th positions varied from 4.95 to 4.99 mm.

I run this cassette in friction mode, since my index shifter for the rear derailleur is a 6-speed model.

'Hope this is helpful.

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Old 07-12-18, 05:12 AM
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I have the 1989 8speed DA-7400. Be aware that dura-ace from that period is different cable pull ratio, different thread on the last cog (is smaller than standard uniglide. so they could fit 11T .. while normal non-duraace uniglide had 13T or 12T)
RD and shifter must be both dura-ace or both non-duraace to work on 8speed indexing (or a weird combo of standard 9speed shifter with dura-ace RD will work ok for 8speed but using only 8 out of the 9clicks the shifter has). Might be true for 7speed as well.

https://www.sheldonbrown.com/dura-ace.html
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Old 07-12-18, 02:06 PM
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Originally Posted by Asi View Post
I have the 1989 8speed DA-7400. Be aware that dura-ace from that period is different cable pull ratio, different thread on the last cog (is smaller than standard uniglide. so they could fit 11T .. while normal non-duraace uniglide had 13T or 12T)
RD and shifter must be both dura-ace or both non-duraace to work on 8speed indexing (or a weird combo of standard 9speed shifter with dura-ace RD will work ok for 8speed but using only 8 out of the 9clicks the shifter has). Might be true for 7speed as well.

https://www.sheldonbrown.com/dura-ace.html
Sheldon is wrong about some of that - Uniglide wasn't replaced by Hyperglide until 1992, and UG cassettes for DA were made through 1994.

The reduced size locking cog is only partially true. Later DA hubs had the larger threading for standard threaded sprockets:
http://www.velobase.com/CompImages/H...65FF7FC9C.jpeg

vs the earlier:
http://www.velobase.com/CompImages/H...4A67CD046.jpeg
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