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Rear Derailleur Won't Shift to Smallest Cog (Under Load)

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Rear Derailleur Won't Shift to Smallest Cog (Under Load)

Old 03-10-14, 12:05 PM
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Aerodee80
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Rear Derailleur Won't Shift to Smallest Cog (Under Load)

Hello,

I have a SRAM 2012 RD on a Tarmac SL4. Even with modest load, it shifts fine from 13t to 12t. But going down further to 11t, it wont shift until I soft pedal for at least half a pedal stroke. What could be causing this issue? W/o load it shifts fine.

I have done the following...

- Changed my cable housing (using Jagwire Race Cable set)
- Cleaned the bottom bracket cable guide
- Cross Routed the derailleur cabling (California Cross)
- Changed the derailleur hangar
- Removed the cassette spacer off my Ultegra 11-28 cassette
- Reduced the tension on my cable as possibly I can while maintaining the shift index.
- Decreased the limit on my lower limit screw (didn't make a difference)
- Decreased the limit on my B screw. Only to the point that it does not affect the shifting to 28t. (However it I now realized that the housing is now too short. Which I will change later)

What else did I miss here?

Thank you
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Old 03-10-14, 12:26 PM
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Dave Mayer
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Originally Posted by Aerodee80 View Post
Hello,

I have a SRAM 2012 RD on a Tarmac SL4. Even with modest load, it shifts fine from 13t to 12t. But going down further to 11t, it wont shift until I soft pedal for at least half a pedal stroke. What could be causing this issue? W/o load it shifts fine.
Looks like you've covered most of the steps correctly. Your rear derailleur housing loop should be tennis-ball sized. Perhaps it is currently too short to allow the derailleur to swing forward so as to better engage the small 11-tooth cog. You appropriately unscrewed the B-screw - that should have helped.

I cannot resist to add:
  • Shift under load? My chain is never under tension when I shift. Perhaps old-school training that involved Regina chains and freewheels. Shifting under load only resulted in horrible grinding noises and broken chains.
  • 11-tooth cogs... If I was contesting finish line sprints at 50mph, then I would need one of these. But I don't, so my cassettes start at either 12 or 13. The 11t cog will always be a challenge for derailleurs due to the larger gap between the upper jockey wheel and the cog. If you have a long derailleur hanger, the problem will be worse. The tigher the gap, the crisper and faster the shifting.
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Old 03-10-14, 02:10 PM
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You reduced the limit on the wrong screw. It's the "high limit" screw that controls the derailleurs stop alignment on your 11 cog. The 11 is your highest gear. Having said that, the limit screw is unlikely your problem, but it could be. You need to readjust the low limit screw, you don't want to throw the chain off into the spokes. I also agree with Dave Mayer that you probably don't need an 11.

The short housing at the rear derailleur should be 12 to 13 inches in length, but it's hard to measure when in operating position, maybe with a fabric tape.
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Old 03-10-14, 02:50 PM
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Originally Posted by Al1943 View Post
You reduced the limit on the wrong screw. It's the "high limit" screw that controls the derailleurs stop alignment on your 11 cog. The 11 is your highest gear. Having said that, the limit screw is unlikely your problem, but it could be. You need to readjust the low limit screw, you don't want to throw the chain off into the spokes. I also agree with Dave Mayer that you probably don't need an 11.

The short housing at the rear derailleur should be 12 to 13 inches in length, but it's hard to measure when in operating position, maybe with a fabric tape.
I misquoted, I adjusted the "low limit" screw. I even watched the alignment on the 11t and the upper pulley move but no difference.

I will find out next when I get a longer housing installed.
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Old 03-10-14, 03:04 PM
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take the load off, pedal lightly,spin.. and the return spring should pull it down to the smallest cog.
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Old 03-10-14, 03:17 PM
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Originally Posted by Aerodee80 View Post
I misquoted, I adjusted the "low limit" screw. I even watched the alignment on the 11t and the upper pulley move but no difference.
Again- if you adjusted the low limit screw you adjusted the wrong screw. The low limit screw is the one that keeps the chain from going into the spokes.
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Old 03-10-14, 03:20 PM
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I had a fluky situation preventing me from getting to the smallest cog. I took a close look and found one of the pivot pins on the cage was starting to come out and was getting in the way of the body moving all the way over. I suppose there is a .01 % chance that you have a pin coming out and it is just brushing the body so that sometimes it prevents it from getting to the small cog.
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Old 03-10-14, 03:27 PM
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Originally Posted by Al1943 View Post
Again- if you adjusted the low limit screw you adjusted the wrong screw. The low limit screw is the one that keeps the chain from going into the spokes.
Exactly. The low limit screw has nothing to do with your High (11 tooth cog) gear alignment.

One more thing: you replaced cable housing with Jagwire? Maybe I'm missing something, but Shimano and Campagnolo sell the highest quality cables and housing that I'm aware of. Low compression, low friction - the good stuff.
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Old 03-10-14, 05:45 PM
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Originally Posted by Dave Mayer View Post
Exactly. The low limit screw has nothing to do with your High (11 tooth cog) gear alignment.

One more thing: you replaced cable housing with Jagwire? Maybe I'm missing something, but Shimano and Campagnolo sell the highest quality cables and housing that I'm aware of. Low compression, low friction - the good stuff.
Dave, it is fairly well accepted now that the Jagwire Pro Road kit is among the best cable kits available bar none. Best braking and best shifting performance I have ever experienced since adopting this kit on all my bikes. Ridiculously low compression outers for both shifting and braking. Both outers are built with longitudinal wire, not coiled wire. Inner wires are coated with Teflon besides the liner supplied. This Jagwire stuff is great.
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Old 03-11-14, 01:05 PM
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You said you replaced the gear hanger. Did you check that the hanger is aligned properly when attached to the rear dropouts? There may be a slight misalignment in the frame.


Good luck. Problems with the rear mech moving to smaller rings can be a real PITA to sort out.
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Old 03-11-14, 01:30 PM
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You said you replaced the gear hanger. Did you check that the hanger is aligned properly
when attached to the rear dropouts? There may be a slight misalignment in the frame.
yes , this .. you have to allign the dropout after you replace it , as it is not automatically good enough ..

your LBS has the tool ..
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Old 03-19-14, 10:56 AM
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The issue is fixed. I switched to a short RD hangar. Spesh normally stocks the SL4 with the longer RD hangar. The short hangar is about 6-8mm closer to the axle.
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