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Dura Ace 7900 issues

post #1 of 17
Thread Starter 
I recently bought an RT-800 with full 7900 kit. I love the bike but I've been having trouble with the RD and right shifter. I've been told by many mechanics that there are known issues with the early 7900 production runs an that later runs have changes that take care of the problems (better RD spring, improved shifter mechanics, etc.). Some mechanics around here in some of the shops will start muttering "F**king Shimano" when you mention 7900 to them .

Specifically, I am having probs with:
  1. The RD shifting up smoothly. The spring does not always pull the chain to the next higher cog smoothly.
  2. When double-downshifting the ratchet in the shifter does not always engage the second shift [<click><click>), thus the RD will shift down two cogs then slip back one. This often results in the chain riding between two cogs . oh boy. dangerous.

I've tried everything I can to address the issues myself (cable upgrades, endless adjusting, calls to Shimano, etc.) I am now in the process of getting warranty replacements for my RD and right shifter from Shimano. This, of course, takes a long time and is going to cost me more money.

Any one else have similar issues? What did you do?
post #2 of 17

Re: Dura Ace 7900 issues

Quote:
Originally Posted by pdelappe View Post
I recently bought an RT-800 with full 7900 kit. I love the bike but I've been having trouble with the RD and right shifter. I've been told by many mechanics that there are known issues with the early 7900 production runs an that later runs have changes that take care of the problems (better RD spring, improved shifter mechanics, etc.). Some mechanics around here in some of the shops will start muttering "F**king Shimano" when you mention 7900 to them .

Specifically, I am having probs with:
  1. The RD shifting up smoothly. The spring does not always pull the chain to the next higher cog smoothly.
  2. When double-downshifting the ratchet in the shifter does not always engage the second shift [<click><click>), thus the RD will shift down two cogs then slip back one. This often results in the chain riding between two cogs . oh boy. dangerous.
I've tried everything I can to address the issues myself (cable upgrades, endless adjusting, calls to Shimano, etc.) I am now in the process of getting warranty replacements for my RD and right shifter from Shimano. This, of course, takes a long time and is going to cost me more money.

Any one else have similar issues? What did you do?
I don't know if the mechanics inside the DA shifter are actually causing your problem, OR NOT ...

Presuming you're willing to do a little more fiddling before you send the shifter & derailleur back to Shimano, then I recommend you remove the derailleur cable housing which Shimano supplied (which is what I presume you are using) that I presume has the same close-to-zero tolerance inner diameter & parallel stranded construction as the stuff Shimano supplied 10 years ago ... AND, replace it with a piece of GENERIC/(coiled core) BRAKE CABLE HOUSING ... you can spend more (e.g., NOKON brake cable housing), but why bother?

Be sure that you debur the ends of the housing with a FLAT FILE & run a spoke into the ends of the housing to ensure that they are clear.

Re-LUBE the cable with a dab of VASELINE before feeding it into the housing.

Tape the housing onto your handlebar ... attach the end of the cable to the derailleur ... test.

If you are keen to use parallel stranded, derailleur cable housing, then get a set of Campagnolo cables & housing ...

And then, REMEMBER, YOU MUST USE THE CAPS ON BOTH ENDS OF THE PARALLEL STRANDED, DERAILLEUR CABLE HOUSING.
post #3 of 17
Thread Starter 

Re: Dura Ace 7900 issues

Thanks for your suggestions. I've tried all of these. I won't bore you with the details. The Shimano
cables were the first to go -- many recommend doing this. Teflon? no go, parallel strands? no joy.

The shifter problem is absolutely positively a defect of the internal ratchet.

Seriously. Early 7900 is defective. Shimano are resistant but they are honoring my warranty.

My question still stands:
Has anyone else experienced these problems?
post #4 of 17

Re: Dura Ace 7900 issues

The bike shop I work in has installed, sold and serviced dozens of bikes with DA7900 and I have yet to see one that gave us any real problems getting to run perfectly.

That being said on bikes with lots of internal cable routing you can get some problems due to the weird bends. In these cases we normally just replace the cables with the new Jagwire 1.1mm sets.
post #5 of 17

Re: Dura Ace 7900 issues

Sounds like you have it narrowed down but. A friend I ride with bought a new Tarmac last summer and was having issues with RD performance on his 7900, they tried everything in the shop same as you. One time in shop one of the mechanics was watching gears work from behind and he noticed the RD kinda sitting funny, hard to explain how he described it because of his heavy east european accent. Anyway took the RD off the bike and were the bolt attched to hanger there was a huge build up of paint from the factory, sanded paint off reinstalled RD, problem gone.
post #6 of 17
Thread Starter 

Re: Dura Ace 7900 issues

Good point on the internal cable crossover potential. That's messed me up in the past.
post #7 of 17

Re: Dura Ace 7900 issues

I have the same problem with a Trek Madone 6.2 with Ultegra. The shifts are sloppy and the chain rubs the cassette. For some reason, the entire gruppo is Ultegra, except the cassette, which was 105. The dealer said there is no difference aside from weight, and tried a SRAM cassette - however, the problem is worse. Will probably get my old bike from the dealer (2.3 aluminum with full 105) - it has external cables and the aluminum hurts the joints with 50+ mile rides, but it shifts smoother than a caddy!!
post #8 of 17

Re: Dura Ace 7900 issues

Agree with others. Assuming derailleur is properly adjusted you will want to confirm cable slides easily in housing. My guess is that it doesn't.

make sure you don't have and tight bends. If you buy new cables\housing make sure you don't cut it too short and end up with tight bends especially at the rear.
post #9 of 17

Re: Dura Ace 7900 issues

I've just built up a second bike and can tell you from experience (as have others replying to this thread) that cable housings that aren't cut cleanly can affect the movement of the cable through the housing and no amount of lubricant will fix the problem. If the cable doesn't slide very easily through the housing, go no further...in my view, the FD and (in particular) RD springs just can't compensate for the added resistance. If the cable moves easily, then check for overly-tight cable/housing bends as another source of resistance. I have no shifting problems with my 7900 FD or RD on 2008 Trek Madone 5.2 with 7801 STI shifters.
post #10 of 17

Re: Dura Ace 7900 issues

Whenever I'm faced by a rear derailleur that won't shift properly after I've made all the proper adjustments and I'm sure the cable is sliding freely, I look at the alignment of the derailleur hanger. About 99.8 percent of the time, straightening or replacing the derailleur hanger fixes it.
post #11 of 17

pdelappe, What was the final outcome on your 7900 issues? I'm experiencing the same challenges on my Scott Addict, dealer installed complete 7900 groupset, and the performance to this point is the same as yours...

post #12 of 17

I had all the same problems and tried the same cures as above.  I had been to 3 small local shops in Arizona.  Finally when I went to a major shop on Orange County, Ca they told me the way the solve the problem is to install Sram coated cables.  The bike is a 2011 Roubaix with internal cable routing.  After installing the Sram cables all the problems went away and the bike shifts perfectly.  The repair guy at the shop explained they have found that the 7900 shifter and derailurer are increably touchy to any, and they emphasized any, friction in the cables.  Hope this helps.

post #13 of 17

Thanks for the reply desertrider.....

post #14 of 17

Is the problem totally consistent, or does it sometimes happen and sometimes not?  A bike from that specific time period may also have the shimano chain quick link, which they discontinued almost immediately because of various problems.  If you do have the shimano quick link, and your problem is intermittent, see if you can watch it closely on the stand to see if the problems only occur when the quick link is in the derailleur or on the cassette.  

 

(Actually if you have the quick link, you should remove it anyway (lose a link if you can, or get a new chain), even if it's not the cause of the problems.)

post #15 of 17

Have had endless problems with my early (2009) DA rear shifting. It's never been smooth and accurate. I've rerouted the cable coming out of the STI (alternative routing), and run it on along the bottom of the bars. Gentler bends using a longer cable housing. Securely attached metal (not plastic) caps.  It works ok now (altho sometimes almost hesitates shifting). Basically seems like there are some bandaids to solve design problems (ratchet springs too weak?). I am going to replace the RD and see if that helps any. 

 

Have a 2011 Ultegra 6700 group on another bike. Shimano did it right. Bulletproof positive shifts. Slightly more force needed at the STI. 

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