Shimano D/A RD-7700 for 10 spd?

Lonnie Utah said:

Hi all,

I heard a dirty little rumor that the "old" (last years) Shimano Dura-Ace RD-7700-GS will work with 10 speed. If that's true, I'm thinking about swaping out my current 10spd D/A derailier so I can have more flexability with the rear casette. I'm running a 50/34 in the front and a 11x23 in the rear, but would like the flexability to use up to a 12x27 in the rear. That's beyond the specs of the current 10 spd derailer. If the 7700-gs will work that would be awesome. The $100, I would have to spend would be a bit much, but that's another story...

L

It stands to reason to those of us who are not engineers that if you can use a Shimano 10-speed rear derailleur with a 9-speed drivetrain by anchoring the rear derailleur cable in the alternate 9 o'clock position, then if you were to anchor the rear derailleur cable in the hubbub.com alternate anchor position at 3 o'clock, the 9-speed Shimano rear derailleur will be index for a 10-speed cassette.

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This alternate anchor position was pioneered to utilize a 9-speed Shimano rear derailleur with a 10-speed Campagnolo ERGO shifters & 9-speed Shimano cassette (hence, the picture of a 9-speed XT rear derailleur) ...

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I'm sure one of the "engineers" who monitor this forum may suggest the JTEK Shiftmate ...

WHY is your 10-speed D/A rear derailleur incapable of being used?

If it is simply a matter of chain capacity, then why don't you just swap the 13t jockey wheels from the 7700-gs for the 11t wheels in the 7800?

I've only glanced at pulley wheels on the 10-speed rear derailleur that I have, so I don't know if the wheels are too thick for the 10-speed chain ... I think they are the same width ... but, if needed, you could spend 2-minutes with a flat file if the teeth need to be narrowed ...

You can buy replacement, 13t jockey wheels if you don't want to cannibalize your 7703-GS rear derailleur ... apparently, there are two different prices depending on whether the jockey wheel is for the "upper" or "lower" position ... the "lower" wheel is cheaper. I don't know that the rear derailleur cares ...

You could always change the cage, itself, with one from a 105-or-Ultegra xx03 rear derailleur ... not as easy to do, but it may not cost any more than the 13t pulley wheels.

That combination of teeth is out of specs. The total chain link uptake capacity for the 7800-ss (which I currently have) is 29. If I wanted to run a 12x27 rear cassette with the 50x34 compact double that I have it works out like this

50-34 = 16
27-12 = 15

16+15 = 31

With the longer cage derailluer the capcity goes up to 37 so it would work better.

From what I've been told here, there is no reason you can't run the short cage deraillure out of specs, but it is at your own risk. That's most likley what I'll do. Either that or sell the 10spd ultegra 12x27 and get a 12x25 instead, bringing the system into spec. But I didn't think that combination was THAT much more benificial that the 11x23 that's on there now, so why spend the money? Honestly I've cranked up some pretty steep stuff with the 34x23 (10% for more than 1 mile) and while my cadences have been low, it really hasn't been that much of a problem. It would just be nice to have a bail out option. Anybody want to buy a 10spd cassette with less that 5 miles on it? 😉

L

Lonnie Utah said:

That combination of teeth is out of specs. The total chain link uptake capacity for the 7800-ss (which I currently have) is 29. If I wanted to run a 12x27 rear cassette with the 50x34 compact double that I have it works out like this

50-34 = 16
27-12 = 15

16+15 = 31

With the longer cage derailluer the capcity goes up to 37 so it would work better.

From what I've been told here, there is no reason you can't run the short cage deraillure out of specs, but it is at your own risk. That's most likley what I'll do. Either that or sell the 10spd ultegra 12x27 and get a 12x25 instead, bringing the system into spec. But I didn't think that combination was THAT much more benificial that the 11x23 that's on there now, so why spend the money? Honestly I've cranked up some pretty steep stuff with the 34x23 (10% for more than 1 mile) and while my cadences have been low, it really hasn't been that much of a problem. It would just be nice to have a bail out option. Anybody want to buy a 10spd cassette with less that 5 miles on it? 😉

L

Sorry, let me try this again ...

There is little reason that I can see why you can't swap the 11t pulley wheels in your 7800-SS rear derailleur with the 13t pulley wheels from your 7703-GS rear derailleur other than the psychological trauma a (temporarily) cannibalizing one to benefit the other ...

I think the 7703-GS cage is fractionally longer (is that right), so your increase in chain capacity will only be the 4t differential in the pulley wheels ... that gives you a theoretical capacity of 33t if you change both pulley wheels, and 31t if you only change the trailing/"lower" pulley wheel (see attachment) ...

The particular pulley wheel (sorry the pic is so small) is from a cheap mega- rear derailleur ... the particular 13t pulley wheel's bushings were too wide because it was for a 7-speed derailleur & it needed to be narrowed to fit the 950 cage, but the teeth were fine. I wanted to "test" fit the 13t pulley wheel before buying a 13t pulley wheel from a 7703 rear derailleur for the above pictured XTR rear derailleur ... but, it works so well, that I figure "why bother until it wears out?"

The hubbub.com alternate anchoring SHOULD BE viable, and you have nothing to lose by trying it other than the time it takes to remove the 7800-SS rear derailleur from your bike and putting the 7703-GS rear derailleur on in its place.

If the rear derailleur cable is anchored as shown in the hubbub.com position, it will NOT slip ... at least MY limited experience is that should not be a concern.

Ok, maybe I wasn't clear either. I only own the 7800-ss at this point. I was going to purchase a new one to replace it. I understand what you are saying (which is really cool), but I don't have the parts to do what you are suggesting without making a purchase of something...

L

Lonnie Utah said:

Ok, maybe I wasn't clear either. I only own the 7800-ss at this point. I was going to purchase a new one to replace it. I understand what you are saying (which is really cool), but I don't have the parts to do what you are suggesting without making a purchase of something...

L

Oh, okay ...

FWIW. The 13t pulley wheels used to be available at JENSONUSA (www.jensonusa.com) ... something like $13 & $18, respectively ... certainly, your bike shop can order ONE ...

If you do decide to buy a new rear derailleur, you may want to consider the 105 ... VeloNews recently noted (more related to the shifters) that the quality of the 105 was much closer to DA than in the past ...

And, my limited observation is the difference between the various Shimano front & rear derailleurs is minimal -- mostly weight & finish. So, if 105 troubles your sensibilities, you could get an Ultegra 6603 rear derailleur.

Lonnie Utah said:

Ok, maybe I wasn't clear either. I only own the 7800-ss at this point. I was going to purchase a new one to replace it. I understand what you are saying (which is really cool), but I don't have the parts to do what you are suggesting without making a purchase of something...

L

Just put it on. The capacity is only going to be a problem if you accidentally shift into the big-big combo.

artmichalek said:

Just put it on. The capacity is only going to be a problem if you accidentally shift into the big-big combo.

Yeah, I know (Unfortunately, against mine and everyone elses better judgement, I do that too frequently). Here's another question, I've never gotten consistent shifts out of the 12x27 (it seems to skip, alot). Ideas?