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Old 10-29-05, 09:33 PM   #1
bandregg
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vertical chain jumping - rear derailleur

I have a newly installed campy 10 speed double drivetrain with bar-end shifters. With the chain shifted to the smallest cog in the cassette the chain jumps, for lack of a better word. This isn't ghost shifting or bad trimming. The chain actually jumps vertically a little bit ever revolution or so, though speed and force seem to play a part. The rest of the shifting is as smooth as can be, and both the front and rear derailleur seem to be setup perfectlly except for this weird "jump." Has anyone encountered anything like this, or fixed it?

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Old 10-30-05, 01:19 AM   #2
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Sounds like a tight chainlink to me. Turn the crank backward with your hand and watch the chain where it comes out of the derailleur cage. That will help you to identify if you have one.
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Old 10-30-05, 07:35 AM   #3
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Check the travel limit adjustment; if it's "not quite enough" it will not allow the chain to be fully engaged on that last gear.

If it was a tight chain link one would expect it to do this in more than just the one gear...
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Old 10-30-05, 08:22 AM   #4
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Please understand that I defer to the senior members on this, but I had a similiar problem with a Trek 720. After trying other approaches to fix the problem, I realized the previous owner was running a chain that was one link too long and I perpetuated the problem when I replaced the chain. Could it be that with the new set up your chain is one link too long resulting in no tension on the chain on the smallest gear? Just a thought.
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Old 10-30-05, 08:59 AM   #5
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Are you using the correct lockring for your cassette?, and if using a connex link,make sure it is installed correctly.
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Old 10-30-05, 09:16 AM   #6
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A slightly too long chain shouldn't cause this problem unless it is long enough to allow the derailleur to go completely slack in the problem gear. The OP didn't say which chainring the problem happens in or if it occures in both. If it happens in the large ring, a too-long chain isn't likely to be the cause.

The wrong lockring or a poorly adjusted high gear limit screw are more likely. A tight link would be most prominant in the smallest cog since the chain wrap is most severe so that should be checked too.
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Old 10-31-05, 10:30 AM   #7
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I just checked and it does happen when using either chain ring up front. So, to sum it up, that's small sproket in the back (campy lock ring on a campy cassette on a campy hub) with either chainring in the front.

There isn't any problem shifting into or out of this gear, so the limit screws seem to be set right.

The jump happens multiple times per pedal revolution. This is a new chain, so chain wear isn't a problem. When pedalling backward in this gear there are a number of places where the rear derailleur moves downward a couple of milimeters. This could mean there are a number of tight links, but hand checking them doesn't yield anything obvious.
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Old 10-31-05, 12:08 PM   #8
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Do you have an 11T smallest cog? The 11 requires a specific lock ring and the hub you have may have come with the lock ring intended for a 12 or 13T small cog. Campy lockrings come with the hubs, not the cassettes, so it's possible to be "all Campy" and still have the wrong lock ring.
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Old 11-01-05, 08:10 AM   #9
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HillRider has hit the nail on the head.

The Proton wheelset, which comes with a lockring, comes with a 12t lockring. Switching it out to the 11t, which came with the cassette by the way, solved the jumping chain problem beautifully. It should be noted that the two lock rings are distinguishable in look (the 11t has a very flat face, while the 12t has a more rounded face) there are no distinguishing markings to tell which is which.

Now I have a high gear, but this has created another problem. The second smallest sprocket (12t) has started skipping. When I adjust the rear derailleur to fix this the fourth, fifth, and sixth sprocket start skipping. So, I can have 9 speeds in back or a really annoying 10.

Has anyone solved a problem like this, where adjusting for one sprocket throws the others out of wack. I've just been using the barrel adjuster on the rear derailleur. I'll try adjusting the downtube adjuster and the small trim adjuster on the barcon later today.

Thanks finding my stupid mistake thus far.
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Old 11-01-05, 08:30 AM   #10
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Quote:
Originally Posted by bandregg
HillRider has hit the nail on the head.

The Proton wheelset, which comes with a lockring, comes with a 12t lockring. Switching it out to the 11t, which came with the cassette by the way, solved the jumping chain problem beautifully. It should be noted that the two lock rings are distinguishable in look (the 11t has a very flat face, while the 12t has a more rounded face) there are no distinguishing markings to tell which is which.

Now I have a high gear, but this has created another problem. The second smallest sprocket (12t) has started skipping. When I adjust the rear derailleur to fix this the fourth, fifth, and sixth sprocket start skipping. So, I can have 9 speeds in back or a really annoying 10.

[b]Has anyone solved a problem like this, where adjusting for one sprocket throws the others out of wack.[/b I've just been using the barrel adjuster on the rear derailleur. I'll try adjusting the downtube adjuster and the small trim adjuster on the barcon later today.

Thanks finding my stupid mistake thus far.
Read post #5. Critical adjustment may be as fine as 1 click on the adjuster at the RD. Where you make the adjustment is irrevalent.
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Old 11-01-05, 11:12 AM   #11
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The 10s cassette is very sensitive to proper torquing, which is the experience of others and myself.
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