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chain jumping

Old 09-23-08, 03:56 PM
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KasbeKZ
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chain jumping

hi. let me apologize in advance for the possibility that this may have been answered before. but all the threads and articles that i have found have been similar but not exactly the same. so i found it a good idea to ask because the remedies that i have found to use so far haven't worked.

the problem is that my chain (which i just got replaced with a brand new one on the original sprockets) is jumping to lower gears. it doesn't fully shift, but it seems to rub up onto the alligator tooth i believe it's called, and fall right back down, not causing a shift, but causing the pedal to free-fall about an inch. it appears that the derailer may be slightly bent inward, and my teeth all appear to be in good shape. if the bent derailer is the problem, what are the ways that people have found to do it without the special tool? a vise and channel locks? i might add that i've adjusted the barrel on the derailer a few times, in each direction, with little to no change at all, and that this also happens with the chain on any front gear, and only the middle few rear gears. it happens when i pedal harder, and it can happen quite rapidly. perhaps 2-3 jumps in one pedal stoke.

again, sorry if this is a re-post, but i wanted to get a bit more specific answer then what i was finding. sorry for the lengthyness, and thanks for any help.
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Old 09-23-08, 05:03 PM
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If new chain+old cassette=chain hop. Replace the cassette and have a drive line tune up. While your at it, check the cables and housing. If you see any oxidation or fray. Replace with prestretched stainless cables and Teflon coated housing like Jagwire. Do not lube cables and housings, replace them. Lubing them will only cause dirt to collect and gum the cable up. Causing more shifting problems. If you do not have the proper tools and knowledge. Take your bike to a LBS to prevent further damage and cost.
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Old 09-23-08, 05:14 PM
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so the only thing to do is put on a new cassette? why is that? do you think the teeth are messed up any? i've seen worn out one's before, and this one still looks perfect. it's been replaced the last time i replaced the chain. and i believe this chain broke prematurely. i'll go look around for a good place to order one from. do i just need to look for a 7 speed mountain bike cassette? or should i try to find one with the same number on it?
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Old 09-23-08, 07:05 PM
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i looked up some cassettes. thanks for the suggestion. i can't help but think though that the cassette is just fine. it's not that old and i've replaced the chain before without having to replace the cassete and had no problems. do you think i went too long this time. and don't look at this like a contradictory post. i am the first to say that you have a better idea of what's going on then i do. i'm just adding a little more info
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Old 09-23-08, 07:49 PM
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Originally Posted by KasbeKZ View Post
so the only thing to do is put on a new cassette?
No, a bent derailleur or derailleur hanger will cause the problem that you've described. Either get it straightened or replaced. You may need to take it to your LBS if you're not sure how to do that.

Al
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Old 09-23-08, 08:42 PM
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well i'm sure i could get it done, but i've just read that it requires a special tool. i'm mechanically literate, i just liked my bike shop back home so i always took it there. i'm just trying to do it myself now cause i'm a college freshman and very poor.... so with straitening the derailleur, i'm just wondering if i should try doing it without the specific tool, or if that is sure to mess it up
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Old 09-23-08, 08:53 PM
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If everything was fine before the new chain, but the problem started immediately after installing the new chain, then either:

a) You ran the old chain too long, and it stretched so much from wear that it wore the teeth in the cassette, so the cassette must now be replaced.

b) The new chain is too wide for the cassette.

Both have happened to me in the past, but hear "a" happening to people much more often.
I now have a chain-stretch gauge to measure chains whenever I clean them so I don't trash another cassette.
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Old 09-23-08, 09:20 PM
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thanks a lot for all of the advise. i'll go back to the shop and see if they put the wrong size chain on. if not i guess i'm buying the cheapest shimano cassette i can find. saw one for $18. lol this is my getting around bike in case you couldn't tell
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Old 09-24-08, 11:33 AM
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When a cassette cog is worn out the chain skips on the same cog. When a chain auto-shifts from one cog to another either the cable tension is wrong or the derailleur hanger or derailleur is bent, you said it's bent. You should also check for a tight link in the chain, possibly where the chain was joined.
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Old 09-24-08, 01:04 PM
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i'll check for that spot. and i guess this weekend i'll be trying to get the derailleur straitened out. i just really don't think the cassette is worn out though. it's not that old, and it still looks brand new. well, it is old, but it hasn't been used much. thanks for all the suggestions everyone
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Old 09-24-08, 02:42 PM
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If it worked fine nefore you changed the chain, I doubt that the cause is a bent derailleur - unless you neglected to tell us about the crash

Originally Posted by KasbeKZ View Post
the problem is that my chain (which i just got replaced with a brand new one on the original sprockets) is jumping to lower gears. it doesn't fully shift, but it seems to rub up onto the alligator tooth i believe it's called, and fall right back down, not causing a shift,
That symptom is typical of needing to tighten cable tension

i might add that i've adjusted the barrel on the derailer a few times, in each direction, with little to no change at all,
Impossible unless you did not adjust it enough. You should be able to adjust enough to shift at least one cog by turning the barrel adjuster. Try tightening the rear by one full turn at least. FYI, there are about 3 full turns of the adjuster between gears.

and that this also happens with the chain on any front gear, and only the middle few rear gears.
It's possible that they sold you a slightly narrower chain, and/or possibly the bike had been adjusted just at the point of shifting. I doubt that you bent both derailleurs.

Let us know how you do.
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Old 09-24-08, 04:30 PM
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well, i said there was no change when i adjusted it, but there was. the appropriate change i guess, but what i meant was that it didn't help the problem at hand any. i've got a test tomorrow, but i'll get back to it on friday. i'll take it to the bike shop, see what they say, and try a few of the things suggested on here, then post my results. thanks for all the help.
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Old 09-26-08, 02:35 PM
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well, i was wrong. if you guessed that the problem was the free-wheel, you were right. just went to the shop and for a bill of $37 had the free-wheel replaced and all is perfect. i guess my estimate of mileage was FAR off. i haven't ridden the bike in a while, so it was hard to think back that far.
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Old 09-26-08, 03:14 PM
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Freewheel is fine, swapped from another bike, Shimano Dura Ace 9-sp.
Chain is new. 9-sp Shimano Dura Ace.
RD and FD are Shimano Dura Ace 7400 series.
New Jagwire shift cable and housings, routed from 1" below the brake levers.
Bar end shifters are used, only compatible, per the sticker with my RD.
The thing is demon shifting all over the place on my Ti build.

Everything worked fine on prev bikes, except bar enders are added component.
They seem pretty bullet-proof, and the shifts are clicking just fine.

Any suggestions?
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Old 09-26-08, 05:01 PM
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adjust the derailleur?
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Old 09-26-08, 05:19 PM
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perfect on the smallest cog.
perfect on the largest cog.
Spacers are 9s, 9 cogs, 9-sp bar ends, 9-sp RD.
It worked perfectly on an 8-sp Shim 600 STI setup.
Maybe it's time for LBS.
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Old 09-27-08, 08:35 AM
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Originally Posted by KasbeKZ View Post
well, i was wrong. if you guessed that the problem was the free-wheel, you were right. just went to the shop and for a bill of $37 had the free-wheel replaced and all is perfect. i guess my estimate of mileage was FAR off. i haven't ridden the bike in a while, so it was hard to think back that far.
Either the symptoms were not as you stated or you were taken . Freewheel issues generally involve chain suck or cassette slipping. I does not make sense that it be fine until the chain was changed or would cause the FRONT to mis-shift.

BTW, sop of changing the free-wheel would be to adjust the derailleurs , and you're lucky they had a replacement part since freewheel hubs were replaced by freehubs long ago AFAIK

In any case, glad to know you're back on your bike, and $37 is not a bad price to accomplish that.
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Old 09-29-08, 03:10 AM
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It would make sense that the free wheel could cause this problem. But you should have been able to see a bad free wheel by spinning the wheel. A bad free wheel will pitch the cassette laterally along the axle in an orbital motion while coasting. This pitching will miss align the drive line and the dérailleur will not always be in line with the cog as it pitches. I was making some assumptions with my previous answer. I should have asked what make, model, and the group of the bike. Its very important not to mix anything in the drive line that is not 100% compatible. There is a lot of 3rd part stuff out there that is cheap. I would think twice about using it. The drive line parts should all be from quality vender's and proven interchangeable parts. Also judging wear by sight can be difficult. Using gages is the only way to do it. Drive lines are very precision engineered devices. Adjusting cables should be done in 1/4 turn increments. Checking the shifting across the range for that chain ring and cassette combination. This involves knowing cross chain patterns for a particular drive line. Drive lines can get complicated when you start to swap out parts. Especially when messing with bottom brackets, cranks, chain rings, and cassettes. There are several calculations needed to keep the chain in the working drive line to prevent hop and miss shifting. Not to mention clearances on the dérailleurs themselves. If your not mechanical leave this to the shops. Even changing out exact replacement parts. You still need the touch to adjust drive lines correctly. Sheldon Brown and Park Tool are a couple of places to visit for reference mechanical issues. Zinn has very good books on bike maintenance to learn and use as reference.

Last edited by CyclingTony; 09-29-08 at 03:15 AM.
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Old 09-29-08, 08:52 AM
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i don't think it was the inside of the free wheel that was worn out, i think it was just the teeth, so it was spinning just fine. but, agreed, some frequent measurements would have saved me some money
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