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PostPosted: Sat Dec 08, 2012 8:14 pm 
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Joined: Wed Aug 02, 2006 3:55 pm
Posts: 68
Location: Menlo Park, CA
Riding a new Cannondale Evo with Sram red group from 2012. I've had several episodes of chain drop when shifting from front large ring to smaller ring despite several tunings by LBS. I've upgraded the front derailleur to 2013 version which is better and also have Praxis 53-36 chain rings which work great. Rear cassette is Sram Red 11-26 which came with bike and just a few months old. LBS says Sram derailleurs are "flexible" and just work as well as Dura Ace group. I was thinking of getting latest Sram rear derailleur to see if there is an improvement but LBS says they are all flexible. Any suggestions? Any feedback on newer X Dome cassette with shifting and precision?


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PostPosted: Sat Dec 08, 2012 8:48 pm 
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53 to 36 is a large drop

I'm running 53/39 Q rings so that could be a 56/36 if you get the timing wrong and have no issues at all. I'm running 11-28 at the rear all Sram Red 2011, recently swapped to 11-28 Powerdome 2012 (much quieter). I have no problems shifting at all, and I've also played a lot with my rear derailer with lightweight jockeys, bolts and carbon cage so if anything it flexes even more now

This will either be an adjustment issue (need to move inner stop screw on front derailer) or the crank rings are not right, reversed, not sat correctly or not bolted up tight or flexing, so that gap between them is not right)

Could also be a sticky/bent tooth on the rings or a sticky chain link

When does it drop, under power, fast change/slow change etc?

S

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Posted: Sat Dec 08, 2012 8:48 pm 


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PostPosted: Sat Dec 08, 2012 9:12 pm 
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No need to adjust and a new rear derailleur.
Get a chain catcher .This will solve your problem.

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PostPosted: Sat Dec 08, 2012 9:55 pm 
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Location: Volos GR / CT US .
The 2013 front Red derailleur he's using has a chaincatcher built in.

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PostPosted: Sat Dec 08, 2012 10:58 pm 
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Location: Menlo Park, CA
Thanks for the feedback and suggestions. The chain drop has occurred off the front when shifting and under load. More concerning is chain drop in the rear off the large gear into the wheel between the spokes and cassette. This too happens when shifting and under load. I remember it occurred once up a steep hill when I attempted to shift down to the lowest gear but was already in the lowest gear. It's happened a couple of other times but I can't recall the specific sequence of events other than suddenly finding the chain caught between the spokes and cassette. Just got new wheel set and want to avoid it happening again.


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PostPosted: Sat Dec 08, 2012 11:01 pm 
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In that case the stops are set incorrectly front and rear

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PostPosted: Sat Dec 08, 2012 11:04 pm 
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Location: Menlo Park, CA
Thanks! Got it. I'll look carefully at those settings. Any reason to change rear derailleur to 2012/2013 version?


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PostPosted: Sat Dec 08, 2012 11:09 pm 
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Location: Canada
Your derailleurs are not properly adjusted. Your high and low limits need to be set then your cable tension to ensure proper shifting. I'm guessing if your chain catcher isn't catching your chain then that should need proper setup as well.

No amount of new parts can fix improper installation techniques....

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PostPosted: Sun Dec 09, 2012 12:18 am 
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If your LBS could not solve a front chain drop issue, WITH a chain catcher, go somewhere else. Ask other cyclists who they think is the best mechanic within an hour drive, call and make sure he's in when you want to go in. An hour is a pain, but totally worth it if you no longer have problems.
I wouldn't be surprised if the new mechanic then points out other things seriously out of spec with your bike's setup that you weren't even aware of.


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PostPosted: Sun Dec 09, 2012 12:54 am 
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Location: NYC
bura wrote:
No need to adjust and a new rear derailleur.
Get a chain catcher .This will solve your problem.



Really poor advice...a chain catcher is never a substitute for a poorly adjusted der. As others have mentioned, if your "mechanic" has not been able to address what appears to be a very simple mechanical adjustment, then you should really seek another mechanic. There are several factors that need to considerer, in addition to properly setting limit screws for BOTH front and rear ders, you should also inspect cable tension, rear der hanger alignment (with proper tool, not eye balling) , chain length and finally make sure there are no bent or stiff links in chain and bent or chipped teeth on your chainrings. EM3

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Last edited by em3 on Sun Dec 09, 2012 6:45 am, edited 1 time in total.

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PostPosted: Sun Dec 09, 2012 12:58 am 
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Location: Menlo Park, CA
Thanks for the advice. LBS in Palo Alto has good reputation with very knowledgeable mechanics. Will investigate further.


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PostPosted: Sun Dec 09, 2012 3:52 am 
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Location: Santa Cruz, California, USA
Changing the rear derailleur or cassette isn't going to have much effect on dropping the chain on front shifts.

Have you checked the front derailleur adjustment? Shift into the large cog and turn in the low stop until you hear the chain hitting the cage when turning the cranks. Adjust the stop until the chain just stops rubbing on the cage. That will be out as far as practical. The Sram adjusting screws have a coarse pitch and don't need much to change the adjustment significantly.

If it's still throwing chains after correct adjustment, then you need to change the angle of the cage. To reduce throwing chains to the inside, aim the cage out (tail in). It's complicated due to the Yaw feature which changes cage angle based on position. Of course you'll need to re-adjust the stops and perhaps the cable tension.

In any case a chain catcher is still a good idea. It's not a replacement for a correctly adjusted derailleur but even a correctly adjusted derailleur can sometimes throw a chain if you shift while hitting a bump.

The Sram catcher is good but the few times it's caught a chain for me the derailleur alignment has changed, requiring adjustment.


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PostPosted: Sun Dec 09, 2012 10:30 am 
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Yiannis-Super 6. wrote:
The 2013 front Red derailleur he's using has a chaincatcher built in.

Thanks. I did miss that. :oops:

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Posted: Sun Dec 09, 2012 10:30 am 


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