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Gear jumping(12 posts)

Gear jumpingSkip
Oct 27, 2002 5:30 PM
What could be the cause for occassional gear jumping, up/down/up/down between two consecutive gears, while pedalling under moderate pressure? It only happens between 2-3 of the center gears of the cassette, and it occurs while in either one of the front rings. Thanks.
Rear derailleur is out of adjustment (nm)roadiebrodie
Oct 27, 2002 5:34 PM
re: Gear jumpingmackgoo
Oct 27, 2002 5:34 PM
Did you by chance replace your chain? I did just that a while ago and found that this would hapen on my 17 of an 11-21. I made all kinds of cable adjustments to no success, about 100 mile latter evrything worked in and the skip is gone.
Don't ask me why.
re: Gear jumpingMcAndrus
Oct 28, 2002 4:41 AM
Three possibilities.

- Rear derailleur out of adjustment.
- Worn chain skipping over your cogs.
- Worn cogs where teeth do not correctly mesh with the chain.
Exactly. If you have not replaced either recently, then...rtyszko
Oct 28, 2002 5:30 AM
it's time to replace both. If you recently replaced one or the other, then replace the other. Sometimes you can get away with a chain replacement only, but when you start getting "auto-shifting" it's time to replace them both.

Bob
re: Gear jumpingChen2
Oct 28, 2002 6:44 AM
Try adjusting the cable at the rear barrel adjustor. Counter-clockwise adds tension. If you get it too tight it won't shift to the smallest cog.
~Al
re: Gear jumpingGeardaddy
Oct 28, 2002 10:54 AM
The possibilities (in order of least to most involved solution):

1) Cable tension out of adjustment - tweak either at rear derailler or at shifter (if yours has a shifter adjustment)
2) Stiff chain link - find it and loosen it.
3) Loose chain link (Do you hear the telltale "ticking" sound when pedalling?) - find it and fix it, or replace chain if you want.
4) "Sticky" cable action - replace cables and/or housings.
5) Worn chain (Does your chain actually stretch or have "play" in the links?) - replace chain at least.
6) Worn cassette cogs (Are cogs worn down or "scalloped"?) - replace cassette AND chain.
re: Gear jumpingSkip
Oct 28, 2002 1:16 PM
Thanks for everyone's responses. Of those listed, I would go with the derrailler possibly needing adjustment. The chain has never been repeatedly removed/replaced or damaged to my knowledge, and I only have approx. 800 miles on the chain & cassette. Well cleaned & lubed with Pro-Link.

What I can't understand is why does this only happen in the center of the cassette (15 & 17), not at either end - the gears 12,13,14,... or 19, 21, 24, or 27? If the derrailler was out of adjustment, wouldn't it jump in all gears? Thanks.
re: Gear jumpingGeardaddy
Oct 28, 2002 1:54 PM
The fact that it only happens on your 15 and 17 makes me think that it is not a derailler adjustment, rather it is more likely that the cable is "sticky" at that particular position or one of those particular cogs is worn.

Also, just because the chain hasn't been repeatedly removed/replaced doesn't mean that it can't have a stiff or loose link. Repeated tensioning of the chain, regardless of how often you clean and lube, can still cause these conditions to develop. Just rotate the pedals slowly backwards and look closely at the chain as it goes through the rear derailler. You should be able to spot a stiff or loose link with the naked eye.
re: Gear jumpingmackgoo
Oct 28, 2002 2:44 PM
For a Campy derailleur you would set the limit screws then adjust your cable at the 15 tooth.
And then there's frame flexKerry
Oct 28, 2002 4:56 PM
Back in the day, flexy frames were a common cause of "ghost shifting." The back end would move enough to cause the cable to slacken and then you'd shift to the next smaller cog. Any strong rider could make it happen with many of the 60s and 70s frames from the low end of the spectrum. Any chance you've got a superlight that can't take the pressure? Otherwise, you've gotten good advice from the other posts.
And then there's frame flexSkip
Oct 28, 2002 6:14 PM
Thanks Kerry & all. My bike is a Merlin Extralight, but I would think that it's stiff enough - but could be wrong. I wouldn't say that I'm hammering, but rather only moderate pressure on level terrain.

I was concerned also about the possibility of a bent/tweeked derrailer hanger as a possible cause - sure hope not. Would be much more relieved if it's only a cable that needs lube, derrailler adjustment, etc. Thanks for all input.