Bike Repair Question

I ride a geared bike that's been giving me a bit of trouble lately: My chain skips, either on it's own, or to a new cog almost constantly. I've put a few thousand miles on the bike in the past three years, and am pretty up on bike mainenance. I've put on a new chain, checked for tight links, and adjusted my rear deraileur 'til my eyes crossed. Visually, it doesn't look like my cassette is bad, but it does have a lot of miles, and I'm hoping my deraileur's not bent. Anyone have any ideas? Or is it time to take it to Uptown Bikes?

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Permalink Reply by David Travis on August 28, 2009 at 10:39am
Even though its a new chain, you should inspect every link and pin carefully for alignment and for flexibility. Also you should be sure the chain is the right length and not too long. Usually, you will have to reduce the length of a chain to fit properly. (Without going through the derailleur, you should find the length it takes to wrap around the largest chainring and the largest cog and then add an inch, which is two links). Also be sure it runs through the derailleur cogs correctly.

A second culprit can be a weakened spring in the derailleur. If it is not quite strong enough it does not move down instantly to a higher gear on the cassette when you shift (release its tension) with the lever. If you shift and nothing happens and then it shifts a later to a new cog seemingly "on its own," its probably a weak derailleur spring. In my case, it did not happen when shifting into easier gears (lower gears) because the action that the spring performs in shifting up to higher gears (that is "downhill" into the smaller diameter cogs on the cassette) is done by your levering the shifter making the derailleur/chain "climb up the hill of the cassette" so no spring is necessary. See if it only skips into a higher gears. That should give you a clue.

Also old worn derailleur pivots create their own problems in shifting. And, of course, shifting when the bike and drivetrain are stopped and you are not pedaling, will cause all kinds of nastiness. (Sounds like you are not doing this, however.)

There's always a reason, but sometimes it's surrounded by a mystery. Let us know what the solution was when you get to it.

And good luck.
Permalink Reply by Gecko on August 28, 2009 at 11:01am
Most often I would suggest replacing the chain and cassette together, as they wear out at similar rates and in a way specific to both. Your derailleur hanger could also be bent, which would affect the shifting no matter what you do to the derailleur. Both are easy fixes.

Just for information's sake, what type of cassette/chain/derailleur are you running, how many miles are on everything, and did you make sure you cut the new chain to the exact same length as the old chain when you put it on? I could help answer your question a little better with that information.
Permalink Reply by Duppie on August 28, 2009 at 11:37am
Does it skip while staying in the same gear? Does it only do that while in a smaller cog?
I had the same problem and it appeared to be the spring in the pivot point that attaches to the derailleur hanger was rusted/stuck. Therefore the derailleur and cage would not move forward when shifting into a smaller cog and be too far backward, causing the skipping. I am trying to loosen it up with Liquid Wrench, but no luck sofar. My LBS (Uptown Bikes) showed me how to take that pivot point apart, so that is the next step. I am slowly getting used to the idea that I have to buy a new derailleur.
Frank
Permalink Reply by Phil Szyjka on August 29, 2009 at 11:16am
Check the Cassette for wear as suggested, Also check the derail. hanger for alignment issues, this is almost always the culprit.
Permalink Reply by 329Cycles Adam Kishanov on August 29, 2009 at 7:46pm
Check the pulleys on the rear deraileur easy fix to replace them. see if they spin freely without the chain on.
Permalink Reply by Ben O'Neil on August 30, 2009 at 7:12am
I have a ten speed with a Shimano deraileur system. I'm not sure on the type of chain, but it's the third time I've replaced the chain, I usually do it once or twice a season. There's probably 8,000 miles on the cassette.

El Gecko said:
Most often I would suggest replacing the chain and cassette together, as they wear out at similar rates and in a way specific to both. Your derailleur hanger could also be bent, which would affect the shifting no matter what you do to the derailleur. Both are easy fixes.

Just for information's sake, what type of cassette/chain/derailleur are you running, how many miles are on everything, and did you make sure you cut the new chain to the exact same length as the old chain when you put it on? I could help answer your question a little better with that information.
Permalink Reply by Chucko on August 30, 2009 at 12:22pm
Have you looked at the derailleur hanger? If it's bent, that can cause the problems you're describing, even if the rest of the drivetrain is tuned in properly.

http://www.parktool.com/repair/readhowto.asp?id=39
Permalink Reply by Gecko on August 31, 2009 at 3:26am
8,000 miles on a cassette is pretty good, I'd venture to guess that it finally kicked the bucket. Does it skip while you're adjusting it in the stand, or only while riding/under load?

Ben O'Neil said:
I have a ten speed with a Shimano deraileur system. I'm not sure on the type of chain, but it's the third time I've replaced the chain, I usually do it once or twice a season. There's probably 8,000 miles on the cassette.

El Gecko said:
Most often I would suggest replacing the chain and cassette together, as they wear out at similar rates and in a way specific to both. Your derailleur hanger could also be bent, which would affect the shifting no matter what you do to the derailleur. Both are easy fixes.

Just for information's sake, what type of cassette/chain/derailleur are you running, how many miles are on everything, and did you make sure you cut the new chain to the exact same length as the old chain when you put it on? I could help answer your question a little better with that information.
Permalink Reply by David Travis on August 31, 2009 at 3:38am
If your mystery persists, you might look at the short discussion by Jobst Brandt about skipping chains at;
http://www.sheldonbrown.com/brandt/chain-care.html
By now you are probably getting too much advice. Good luck.
Permalink Reply by Ben O'Neil on August 31, 2009 at 7:17am
On visual inspection, it doesn't appear bent.

Chucko said:
Have you looked at the derailleur hanger? If it's bent, that can cause the problems you're describing, even if the rest of the drivetrain is tuned in properly.

http://www.parktool.com/repair/readhowto.asp?id=39
Permalink Reply by Ben O'Neil on August 31, 2009 at 7:18am
Only under load.

El Gecko said:
8,000 miles on a cassette is pretty good, I'd venture to guess that it finally kicked the bucket. Does it skip while you're adjusting it in the stand, or only while riding/under load?

Ben O'Neil said:
I have a ten speed with a Shimano deraileur system. I'm not sure on the type of chain, but it's the third time I've replaced the chain, I usually do it once or twice a season. There's probably 8,000 miles on the cassette.

El Gecko said:
Most often I would suggest replacing the chain and cassette together, as they wear out at similar rates and in a way specific to both. Your derailleur hanger could also be bent, which would affect the shifting no matter what you do to the derailleur. Both are easy fixes.

Just for information's sake, what type of cassette/chain/derailleur are you running, how many miles are on everything, and did you make sure you cut the new chain to the exact same length as the old chain when you put it on? I could help answer your question a little better with that information.
Permalink Reply by Gecko on August 31, 2009 at 7:39am
I would assume your cassette has finally worn out. I've got an old XT 9spd cassette with similar mileage which is beginning to exhibit the same symptoms with a brand new chain. I would take the whole bike to a shop (not just the wheel) and have them put a new cassette on (if they're smart, they'll also tune the rear derailleur after they put the wheel back on). Then test ride it at the shop, making sure to really crank on all the gears at least once, checking for skipping. If you still have problems, take it back in and see what they think, but I'm almost positive the cassette will fix the skipping issue. One more thing, I know you couldn't remember what kind of chain you had, but have the shop make sure that it's the correct size and type for your shifting system. There are a ton of different types of chains out there and it's really easy to miss a digit in a part number and end up with something completely different than what you need.

Ben O'Neil said:
Only under load.
El Gecko said:
8,000 miles on a cassette is pretty good, I'd venture to guess that it finally kicked the bucket. Does it skip while you're adjusting it in the stand, or only while riding/under load?

Ben O'Neil said:
I have a ten speed with a Shimano deraileur system. I'm not sure on the type of chain, but it's the third time I've replaced the chain, I usually do it once or twice a season. There's probably 8,000 miles on the cassette.

El Gecko said:
Most often I would suggest replacing the chain and cassette together, as they wear out at similar rates and in a way specific to both. Your derailleur hanger could also be bent, which would affect the shifting no matter what you do to the derailleur. Both are easy fixes.

Just for information's sake, what type of cassette/chain/derailleur are you running, how many miles are on everything, and did you make sure you cut the new chain to the exact same length as the old chain when you put it on? I could help answer your question a little better with that information.

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