# Are Dura-Ace 7900 Brifters compatible with Ultegra 6700 Derailleurs?



## sqwk77 (Sep 13, 2010)

Sorry I know Ive seen the answer on here somewhere but can't seem to find it through search.

Thanks


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## Ventruck (Mar 9, 2009)

Yep

Said in another thread that 5700/6700/7900 are cross compatible to a far extent.


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## DaveT (Feb 12, 2004)

You can use a 6700 rear derailleur with the 7900 shifters but not the 6700 front der. A 7900 front derailleur has to be used with those shifters.


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## marathon marke (Nov 14, 2011)

DaveT said:


> You can use a 6700 rear derailleur with the 7900 shifters but not the 6700 front der. A 7900 front derailleur has to be used with those shifters.


That's the way I understood it too. But last week I installed a pair on a Cervelo, and they seem to work fine so far. Do you know exactly why they aren't supposed to work?

I also thought that the brakes won't work as well, possibly due to a change in the lever's pivot point which changes the leverage. Again, seem to work fine.


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## paulfeng (Jun 10, 2011)

[disclaimer: I am not a wrench. (Only an atomic physicist, in a past life.) But that won't stop me from adding to my post count while we wait for someone who knows for sure to chime in.]

I believe that 7900 uses a different cable pull ratio for the front derailleur, so performance might be sub-optimal with a 6700 derailleur. But if it works for you... Also, I believe you lose the ability to trim the front derailleur with the 7900 brifters, which the DA derailleur is designed not to need (via the shape of the cage), but 6700 will generally need as you move toward being cross-chained.

As for brakes, DA 7900, U 6700 and 105 5700 all use compatible lever-caliper cable pulls, which are different than prior generations. (I think more cable movement for a given amount of pad movement?) Levers and calipers can be mixed with other generations, but performance will not be as designed. That said, last summer I rode extensively on a bike with 5700 levers and below-105-level Shimano calipers, and braking performance was fine.


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## sqwk77 (Sep 13, 2010)

Not worried about caliper compatibility as its for a cross bike, but I do need to verify the derailleurs. Sounds like the front may be a no go.

Anybody know for sure? Can't find any answers on the Shimano site.


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## Ventruck (Mar 9, 2009)

sqwk77 said:


> Anybody know for sure? Can't find any answers on the Shimano site.


Shimano's chart says ST-7900 shifters are compatible with only the FD-7900:
http://www.shimano.com/publish/cont...e.html/01) Drivetrain Compatability Chart.pdf

I wasn't convinced to assume incompatibility previously because front derailleurs aren't at all that fancy (at least the non-electric ones), especially when I've read accounts about the cross compatibility between brands in such regards (I myself got Campy Centaur shifters controlling an FD-6600, but let's not stray off-topic).

Best interest to try to just get things matching.


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## DaveT (Feb 12, 2004)

sqwk77 said:


> Not worried about caliper compatibility as its for a cross bike, but I do need to verify the derailleurs. Sounds like the front may be a no go.
> 
> Anybody know for sure? Can't find any answers on the Shimano site.


I have personal experience using 7900 shifters with 6700 and 7800 rear derailleurs and 6700/7800/6600 brake calipers. All worked better than well in those combos. I have no experience using anything other than 7900 front derailleur with the 7900 shifters, but everything that I've read says that a 7900 front der is to be used with those shifters. Anything else won't work properly.


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## nightfend (Mar 15, 2009)

Don't believe Shimano. You can use 7900 shifters with older front and rear derailleurs and it works fine. See plenty of real world examples of this recently.


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## nightfend (Mar 15, 2009)

sqwk77 said:


> Not worried about caliper compatibility as its for a cross bike, but I do need to verify the derailleurs. Sounds like the front may be a no go.
> 
> Anybody know for sure? Can't find any answers on the Shimano site.


Yes, I know for sure. I've seen these bikes ridden in person, and they work fine. My example used 7900 shifters with 7800 rear and front derailleurs.


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## amoz04t (Mar 2, 2018)

The ST-7900 / FD-7900 combo does not have a trim adjustment as does the ST-6700 / FD-6700.


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## cxwrench (Nov 9, 2004)

amoz04t said:


> The ST-7900 / FD-7900 combo does not have a trim adjustment as does the ST-6700 / FD-6700.


Not only are you almost 7 years late...you're wrong. There is a trim on the 7900 shifter for the small ring. 
http://si.shimano.com/pdfs/si/SI-6RT0A-004-ENG.PDF


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## amoz04t (Mar 2, 2018)

I'm sorry, sir - I didn't pay attention to the date stamp of the original question. I hope the person that posted the question received a more timely answer. Haha. And I hope you feel better soon.

I believe my response is correct. I don't see any discussion about the trim function on the SIs for ST-7900 or FD-7900 as I do for ST-6700 and FD-6700. Also, i thought I saw another post that stated that the 7900 Dura-Ace series was the first to eliminate the noise trim function.


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## cxwrench (Nov 9, 2004)

amoz04t said:


> I'm sorry, sir - I didn't pay attention to the date stamp of the original question. I hope the person that posted the question received a more timely answer. Haha. And I hope you feel better soon.
> 
> I believe my response is correct. I don't see any discussion about the trim function on the SIs for ST-7900 or FD-7900 as I do for ST-6700 and FD-6700. Also, i thought I saw another post that stated that the 7900 Dura-Ace series was the first to eliminate the noise trim function.


Click on the link I provided, it describes the small ring trim. Trust me.


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## amoz04t (Mar 2, 2018)

Oh I see that you are referring to the operation of lever "a" to move the FD outward and avoid chain touching the inside surface of the outer plate. This is different that the noise trim function on the ST-6700; that trim uses lever "b" to eliminate noise from chain rub against inner surface of inner plate.

So back to the original question - no a FD-6700 is not compatible with ST-7900.


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## Jay Strongbow (May 8, 2010)

amoz04t said:


> Oh I see that you are referring to the operation of lever "a" to move the FD outward and avoid chain touching the inside surface of the outer plate. This is different that the noise trim function on the ST-6700; that trim uses lever "b" to eliminate noise from chain rub against inner surface of inner plate.
> 
> So back to the original question - no a FD-6700 is not compatible with ST-7900.


I don't understand your first paragraph but what it boils down to is that 7900 levers have trim for the small ring but not the large ring.

I've tried 7900 levers with a 6700 front der. and in that case you are correct. I could not adjust to eliminate rub from the big ring without that trim. But it was real close and that bike had really short chainstays. I may have been able to adjust so trim on the large wasn't needed in the big ring on a bike with much longer chainstays so the angle was less sharp.

Either way, I doubt anyone cares in 2018.


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