Is this a derailleur issue?
06-20-11, 01:08 PM
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Is this a derailleur issue?
A little while ago, I noticed that the spring on the rear derailleur on one of my bicycles didn't seem to be bringing it back up into position when it was on a small chainring and smaller cog. Since I don't use the smallest chainring with the smaller cogs, I haven't worried about it, but I've lately noticed that when in the middle ring, and usually when I'm putting a bit of force on the pedals, the chain will seem to slip, as if it were "autoshifting." However, the chain doesn't shift to a lower cog, and adjusting the shifter (friction bar-end) makes a little difference, but doesn't seem to totally solve the problem. The chain is new, and the cogs are not more than three years old.
Here are some possible causes:
The slack spring--can it cause this kind of thing?
Worn cogs. They didn't seem to bad, although it does seem like the bicycle has had a bit of wear this past winter--one of the eyelets holding the rear rack broke off.
Frame flex when the chain wasn't perfectly in the right place.
Here are some possible causes:
The slack spring--can it cause this kind of thing?
Worn cogs. They didn't seem to bad, although it does seem like the bicycle has had a bit of wear this past winter--one of the eyelets holding the rear rack broke off.
Frame flex when the chain wasn't perfectly in the right place.
06-20-11, 01:17 PM
#2
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May be a case of a chain that is too long and a de-tensioned derailleur... if it is working fine through the rest of the range it is probably this.
The small / small combination is the point where chain tension is the lowest and is usually considered to be a less than optimal gear choice because of the high degree of cross chaining... on a triple you will find the same gear off the middle ring and middle of the cassette / freewheel and enjoy a better chain line and proper tension on the derailleur.
Chain should be measured by removing it from the derailleur and wrapping it around the big chain ring and biggest rear cog and adding a pair of links... the b screw on the derailleur may also need to be adjusted to dial things in to provide adequate tension throughout the entire operating range.
The small / small combination is the point where chain tension is the lowest and is usually considered to be a less than optimal gear choice because of the high degree of cross chaining... on a triple you will find the same gear off the middle ring and middle of the cassette / freewheel and enjoy a better chain line and proper tension on the derailleur.
Chain should be measured by removing it from the derailleur and wrapping it around the big chain ring and biggest rear cog and adding a pair of links... the b screw on the derailleur may also need to be adjusted to dial things in to provide adequate tension throughout the entire operating range.
06-20-11, 01:29 PM
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Chain length was set by the method you described, and the problem described happens when the chain is in the middle ring and about the second or third largest cog. There's no B screw on this derailleur.
06-20-11, 01:32 PM
#4
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A new chain on worn out cogs will cause what feels like a slip. Inspect the cogs for an upset on the leading part of the teeth.
06-20-11, 01:49 PM
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Bicycle Repair Man !!!
Sounds like a wear issue then... am betting that it skips in the gears you use the most.
06-20-11, 01:56 PM
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It sounds as if you may have two problems developing, the chain slipping and the cable slow to return when shifting to a smaller cog.
If the chain slipping problem is not a cable tension adjustment issue then it may be some worn out cassette cogs. But cogs usually last several thousand miles if the chain is not allowed to stretch too much.
I would try shooting WD 40 into the shifters to see if this helps with the sluggish shifting.
I would shift into the smallest chainring and smallest cog. Check to confirm that the derailleur has not reached its forward limit of travel (bottomed out). If it has then the chain is too long or the cage is too short.
And I agree with the others, above.
If the chain slipping problem is not a cable tension adjustment issue then it may be some worn out cassette cogs. But cogs usually last several thousand miles if the chain is not allowed to stretch too much.
I would try shooting WD 40 into the shifters to see if this helps with the sluggish shifting.
I would shift into the smallest chainring and smallest cog. Check to confirm that the derailleur has not reached its forward limit of travel (bottomed out). If it has then the chain is too long or the cage is too short.
And I agree with the others, above.
06-21-11, 09:51 AM
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Thanks for the replies.
As I said in the original post, the shifting isn't sluggish: the problem only seems to happen under force, when I'm accelerating or starting in a highish gear. I replaced cables and housing around Christmas, anyway, so that shouldn't be an issue. And also (see above) the chain is not too long, the derailleur cage seems fine, but the spring that flexes the derailleur is weak.
It might be a wear issue, though. Yesterday I noticed that it was hopping, or whatever you'd call it, in the fourth or fifth from largest cog, which I didn't think I used too often. But I'll observe a bit more.
As I said in the original post, the shifting isn't sluggish: the problem only seems to happen under force, when I'm accelerating or starting in a highish gear. I replaced cables and housing around Christmas, anyway, so that shouldn't be an issue. And also (see above) the chain is not too long, the derailleur cage seems fine, but the spring that flexes the derailleur is weak.
It might be a wear issue, though. Yesterday I noticed that it was hopping, or whatever you'd call it, in the fourth or fifth from largest cog, which I didn't think I used too often. But I'll observe a bit more.
08-31-11, 09:40 AM
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I know it's been a while, but I've solved the problem:
A few weeks ago, I was thinking about whether to buy a new derailleur or new cogs, and decided to take the old derailleur apart. I cleaned up and lubricated the main spring where the derailleur bends in half, put it back together (which was the hard part), and haven't had any problem since. There also is another hole where you can put the end of the spring, which would increase tension and might have helped too, but I didn't try that.
A few weeks ago, I was thinking about whether to buy a new derailleur or new cogs, and decided to take the old derailleur apart. I cleaned up and lubricated the main spring where the derailleur bends in half, put it back together (which was the hard part), and haven't had any problem since. There also is another hole where you can put the end of the spring, which would increase tension and might have helped too, but I didn't try that.
