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Huh...Suntour Accushift works with Dura Ace RD (7402)

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Huh...Suntour Accushift works with Dura Ace RD (7402)

Old 06-17-20, 04:01 PM
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Huh...Suntour Accushift works with Dura Ace RD (7402)

Nothing earth-shattering here, I was just honestly surprised at how well a Suntour Accushift 7 speed downtube shifter worked with a Dura Ace RD (7402). The cassette is a modern Sunrace. A Shimano a400 shifter did not work well at all with the RD. Just noting this for any future bike nerds who may wonder about compatibility.


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Old 06-17-20, 04:22 PM
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So you're saying it works in index mode? I have a set of Accushift that I've yet to install
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Old 06-17-20, 04:56 PM
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I remember it being somewhat well known, back in the early 1990's, that Dura-Ace 74xx shifters and Suntour derailers were compatible enough to work together. I briefly used a 74xx rear derailer with 7s Accushift levers and recall that this worked acceptably Using an Accu-7 freewheel.
This applied to both 6s and 7s (as long as the number of clicks matched the number of cogs).

The Suntour derailer geometry and the Shimano 74xx derailer geometry (cable-to-cage actuation ratio) are actually about the same, and are even apparently the same as pre-index Shimano derailers such as Titlist, 600 and Crane. I doubt if pre-index Suntour derailers are any exception.
But the derailers designed for indexing, and having the slanted parallelogram, are more likely to work well as indexing derailers.

I've also used a Campagnolo Gran Turismo with Shimano 7s indexing levers (with a similar cable travel per click to 6s 74xx shifters, and this setup indexed a 6s freewheel accurately (though indexing required cable adjustment before shifting across the freewheel in the other direction, due to excess chain gap).

The take-away from all this is that most derailers before and immediately after Shimano introduced their very first SIS model have about the same actuation ratio.
One exception to this is the Huret Allvit and Luxe duo (with their asymmetric or variable actuation ratio), but there may be others.

Also, I wouldn't be surprised to find that the "unique" actuation of Suntour's low-cost 3040 model derailer turns out to be the same as Shimano's non-Dura-Ace SIS Actuation, since Shimano couldn't patent their actuation ratio!

And I'm guessing that the old Simplex Prestige and maybe even the Campagnolo Record derailers have about the same actuation as the 74xx, Superbe Pro and earlier derailers from Suntour and Shimano.

Lastly, where Shimano and Suntour differ most is that Suntour used the "faster" actuation of the 74xx and earlier derailers on most of their derailers, with only their 3400 series parts using the longer cable travel and "slower" actuation analogous to Shimano's 64xx and later derailers. In hindsight, Shimano's broader/earlier use of the longer cable travel / lower actuation ratio geometry was the better way to go, as everything designed since then has trended only in this direction.

It's always a challenge to get non-index derailers to index well, mainly due to their little-understood actuation ratios, their lack of any cable adjuster, their non-floating upper pulley, and because of their lack of consistently close proximity of their top pulley to the freewheel cog's teeth (even though their actuation may be about the same).
The older derailers were designed for use with stiff bushing chain and so weren't so good at maintaining a tight chain gap because it wasn't important. But it is important when modern chain is used, even as modern chain better interacts with indexed freewheel's teeth.

For Campagnolo's part, their actuation ratio was slowed to work with newer indexing parts around 1990, exceeding the rest of the industry, until SRAM developed 1:1 (mtb) and "Exact Actuation" (road). Shimano would eventually follow this trend into the modern age.
A 9s Ergolever will thus index properly on a 6-speed Shimano 600 SIS equipped bike.

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Old 06-17-20, 06:42 PM
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For a Trek 400 I recently flipped, I used Accushift down tube shifters, a Suntour ARX rear derailleur (without a barrel adjuster and using brake housing), and a 6-speed Suntour cluster. If it didn't work, I was just going to switch the shifters to friction mode, but it indexed really well. I told the young couple that bought the bike what I did and what it might need down the road, so they could keep it in tune.
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Old 06-18-20, 04:56 AM
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Originally Posted by seedsbelize
So you're saying it works in index mode? I have a set of Accushift that I've yet to install
Yep!
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Old 06-18-20, 05:03 AM
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dddd - thanks for the info! I assume this thread may have touched upon your dissertation? Seriously though - unless a reference book regarding shifter / derailleur / cassette compatibilities already exists, I suggest you publish one. Of course, when all else fails, there's always the info Sheldon left for us.
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Old 06-18-20, 05:07 AM
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Originally Posted by SurferRosa
If it didn't work, I was just going to switch the shifters to friction mode, but it indexed really well.
Sweet! Gotta love those pleasant surprises.
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