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 Post subject: Sticky 7900 Shifter
PostPosted: Tue Mar 06, 2012 8:16 pm 
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Joined: Mon Dec 28, 2009 8:30 pm
Posts: 3935
Location: Bay Area
Odd problem with my right shifter, but it came after riding in some rain so it could be related.

Bike shifts perfect in all gears, but the two cog upshift does not work from the 21->25 (basically from my 3rd largest to largest cog). It almost feels as if it does not engage and the chain falls back down. If I go 1 at a time it works fine.

Anyone think its worth pulling the lever apart and cleaning or had this problem before? I was thinking of doing so, but its a bit of a PITA so I wanted to double check before i did it

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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Wed Mar 07, 2012 2:38 am 
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Joined: Sat Jun 13, 2009 4:02 am
Posts: 1976
Location: NoVA/DC
im pretty sure that is normal.


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 Post subject: Re: Sticky 7900 Shifter
Posted: Wed Mar 07, 2012 2:38 am 


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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Wed Mar 07, 2012 6:10 am 
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Joined: Wed Dec 28, 2011 11:16 pm
Posts: 12
I've had similar issues with older STI shifters (9speed ultegra, etc.). The first thing I do is degrease and then relube (I use triflow, love that stuff and it smells good too). If it works, great, problem solved. If it doesn't, I check the derailleur adjustment settings, especially the low end limit screw in your case. It seems ridiculous but if its dialled in just a bit too close it works fine under single shifts but as soon as you go for a double it jumps up and then back down. Hope you get it all sorted out.


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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Wed Mar 07, 2012 6:40 am 
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Joined: Sat Jun 27, 2009 10:20 pm
Posts: 84
KWalker wrote:
Anyone think its worth pulling the lever apart and cleaning or had this problem before? I was thinking of doing so, but its a bit of a PITA so I wanted to double check before i did it


Are you saying that in the past you have pulled the BLADE off this shifter and gone into the 'guts' of the mechanism?


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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Wed Mar 07, 2012 3:37 pm 
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Joined: Mon Dec 28, 2009 8:30 pm
Posts: 3935
Location: Bay Area
I have, and it sucks. It really, really sucks. You can't fully disassemble it, but you can partially and it takes quite a while.

I checked the limit screws and its super close to going into the spokes on the up shift. This never happened before on either of my last two bikes so its weird that it started with this one. I'll just clean it out and see what pops up I guess.

I put two brand new 7900 bikes in a stand the other day and neither of em did this so I'm 100% sure its not normal.

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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Wed Mar 07, 2012 4:53 pm 
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Joined: Sat Jun 27, 2009 10:20 pm
Posts: 84
Quote:
I put two brand new 7900 bikes in a stand the other day and neither of em did this so I'm 100% sure its not normal.


KWalker wrote:
I have, and it sucks. It really, really sucks. You can't fully disassemble it, but you can partially and it takes quite a while.


You have (2) NEW 7900 bikes at your disposal, sounds like you work in a shop.

So you took it apart. Shimano has always advised everyone, including shop techs to not pull those shifters apart. The shift mechanism under the blade is put together by an automated machine and there is NO way a person can get it back in the correct configuration.


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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Wed Mar 07, 2012 5:14 pm 
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Joined: Mon Dec 28, 2009 8:30 pm
Posts: 3935
Location: Bay Area
I have pulled a 7900 shifter SLIGHTLY apart before. It was also on the warranty shelf, and would no longer be used.

I used to work at a shop, and yes we have two new bikes sitting there just built up to compare to.

This shifter has never been apart. At most I'd take the access plate off just to get a q tip in there to clean off the ratchet a bit better.

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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Wed Mar 07, 2012 7:19 pm 
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Joined: Wed Mar 28, 2007 12:49 pm
Posts: 1581
Location: Near Horgen, Switzerland
Send the shifter back to Shimano - there is a common issue that if you downshift from 8th gear to 10th in one swipe, the chain falls back to 9th. Single shifts from 9th to 10th work fine. I think it only affected the first release of 7900 shifters. Mine took a few weeks but was warrantied without any issues.


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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Wed Mar 07, 2012 7:41 pm 
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Joined: Mon Dec 28, 2009 8:30 pm
Posts: 3935
Location: Bay Area
Word. I don't have a spare bike so its kind of an issue.

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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Thu Mar 08, 2012 2:16 am 
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Joined: Mon Aug 29, 2011 8:55 pm
Posts: 169
Location: New Jersey
How old is the cable? Any chance it's starting to fray inside the shifter and stretching or jamming?


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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Thu Mar 08, 2012 6:29 am 
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Joined: Sat Jun 27, 2009 10:20 pm
Posts: 84
I have had bad shifting develop slowly over time. I never suspected the cable was fraying inside the housing.
Finally took the housing off and there it was, a frayed cable. Happened right were it exits the shifter body.


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 Post subject: Re: Sticky 7900 Shifter
PostPosted: Thu Mar 08, 2012 10:41 am 
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Joined: Mon May 24, 2010 4:18 am
Posts: 382
Location: Australia
Have had this happen before but with old sticky ultegra shifter (6500) with 30000km on the clock. WD40 squirted up the guts followed by lots of shifting. Wipe what drips out with a cloth. Repeat to make sure any grit/old grease is purged. Wipe again and off you go. Probably not brilliant for all of the special internal grease that they use in the shifters.

Could also be grit in your limiter mechanism on your RD.

Cheers,
I


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 Post subject: Re: Sticky 7900 Shifter
Posted: Thu Mar 08, 2012 10:41 am 


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