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Why does my rear derailer skip through gears?

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Why does my rear derailer skip through gears?

Old 11-07-13, 09:44 PM
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Why does my rear derailer skip through gears?

Hello;

I've got the Shimano C101 7 speed rear derailer. It does OK on the biggest and smallest cogs, but skips cogs in the middle. Sometimes it shifts on its own, and sometimes does not shift at all. The cable tension seems to be fine. Any ideas?

Thanks,

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Old 11-07-13, 10:13 PM
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One needs to separate the various reasons a gear system can "skip".

Start with the chain. Does it have tight links? Relaxing the rear der cage spring tension while back pedaling will let a tight link be noticed as it travels through the cog/cage path. Does the chain have any twisted links? Are any side plates pulling off their pins? And the obvious possibility of 'stretched'/worn chain.

Next are the cog/ring teeth. Any twisted/bent? Are the cassette/freewheel cogs all flat against each other with proper spacing between each? Are any cogs broken/cracked or missing teeth?

Next is the ders (rear in this case). Is the cage/pulleys hanging vertically? Are the pulleys straight and intact, no distortions or cracks? Does the chain have clearance through the cage in all cog/ring combos? Are the limit screws set properly (doubt this is the case given the description)? Does the rear der match the cog count and the lever indexing count?

Then the cable. is it routed through the housing and end caps well? Is there undo friction in the path (a much more common problem then many would think)? Is the cable anchored on the correct side of the anchor bolt (another common issue)? Is the cable of the right diameter (1.2/1.1mm)? Is the cable housing the correct compressionless type? Is the cable beginning to fray, say just after it's head in the lever and out of sight? And, of course, is the cable tension set properly?

So there are 18 aspects of index systems that need to be right. Almost every problem is found within this list. Now you need to start looking for your problem. Andy.
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Old 11-08-13, 07:08 AM
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Although I agree with what Andy said the first step is to more thoroughly look at symptoms, so that you don't have to investigate every possible cause (especially as I'm pretty sure I can come up with more). So:

When did the problem start, and were there any changes or incidents that occurred just prior to the symptoms arising? This is one of the most universal and important diagnostic questions for any problem

Is there any difference shifting to larger cogs in the middle range vs. smaller?

Does the skipping happen reliably or does it come and go?

Is there any difference in behavior when you are on different chainrings in front?

Does it skip differently under high, medium or low pedal pressure?
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Old 11-08-13, 10:52 AM
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Not my favorite derailleur.

The first thing that I would do would be to make sure that everything was in the default condition - cables able to move smoothly in the housing, derailleur hanger aligned with the cassette, and cable tension just snug while in the largest cog.

My preferred answer is to replace the derailleur with a Deore.
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Old 11-08-13, 11:26 AM
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That's a lower level DER on the food chain.
What shifters are you using?
Looking at the bikes on your list, there's a possibility your are mis matching???
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Old 11-11-13, 10:38 PM
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Originally Posted by Bill Kapaun View Post
That's a lower level DER on the food chain.
What shifters are you using?
Looking at the bikes on your list, there's a possibility your are mis matching???
Well, it's a lower-level bike on the food chain. It's a Raleigh comfort bike; I purchased it off of someone for dirt cheap, just to use as a temporary bike until I decide on my next real bike. It's comfortable, but has a lot of issues despite being very new. The components are almost laughable. To answer your question, the shifters are just the generic grip shifters that came with the bike.
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Old 11-11-13, 10:44 PM
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Originally Posted by Retro Grouch View Post
Not my favorite derailleur.

The first thing that I would do would be to make sure that everything was in the default condition - cables able to move smoothly in the housing, derailleur hanger aligned with the cassette, and cable tension just snug while in the largest cog.

My preferred answer is to replace the derailleur with a Deore.
I've tried all of your suggestions and all seems to be in order. I'd love to replace the derailleur with a Deore, but that would probably cost more than I paid for the bike.

Then again, having a malfunctioning drivetrain sucks.
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Old 11-11-13, 10:47 PM
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Originally Posted by cny-bikeman View Post
Although I agree with what Andy said the first step is to more thoroughly look at symptoms, so that you don't have to investigate every possible cause (especially as I'm pretty sure I can come up with more). So:

When did the problem start, and were there any changes or incidents that occurred just prior to the symptoms arising? This is one of the most universal and important diagnostic questions for any problem

Is there any difference shifting to larger cogs in the middle range vs. smaller?

Does the skipping happen reliably or does it come and go?

Is there any difference in behavior when you are on different chainrings in front?

Does it skip differently under high, medium or low pedal pressure?
All good questions. I'll keep them in mind on my commute tomorrow, and maybe something will become obvious.

Thanks.
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Old 11-11-13, 10:50 PM
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Originally Posted by Andrew R Stewart View Post
One needs to separate the various reasons a gear system can "skip".

Start with the chain. Does it have tight links? Relaxing the rear der cage spring tension while back pedaling will let a tight link be noticed as it travels through the cog/cage path. Does the chain have any twisted links? Are any side plates pulling off their pins? And the obvious possibility of 'stretched'/worn chain.

Next are the cog/ring teeth. Any twisted/bent? Are the cassette/freewheel cogs all flat against each other with proper spacing between each? Are any cogs broken/cracked or missing teeth?

Next is the ders (rear in this case). Is the cage/pulleys hanging vertically? Are the pulleys straight and intact, no distortions or cracks? Does the chain have clearance through the cage in all cog/ring combos? Are the limit screws set properly (doubt this is the case given the description)? Does the rear der match the cog count and the lever indexing count?

Then the cable. is it routed through the housing and end caps well? Is there undo friction in the path (a much more common problem then many would think)? Is the cable anchored on the correct side of the anchor bolt (another common issue)? Is the cable of the right diameter (1.2/1.1mm)? Is the cable housing the correct compressionless type? Is the cable beginning to fray, say just after it's head in the lever and out of sight? And, of course, is the cable tension set properly?

So there are 18 aspects of index systems that need to be right. Almost every problem is found within this list. Now you need to start looking for your problem. Andy.
Thanks, Andy, for taking the time to write such a long reply.

In the next day or two I'll try to put the bike up on the stand and follow your suggestions.

Thanks
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Old 11-12-13, 01:47 AM
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The first thing I'd look at is whether the RD's sustained any damage, move it through its range of motion looking at the plane of the cage, and feel for slop. Hanger alignment tool shouldn't be necessary, eyeing it up and tweaking the hanger (or entire upper pivot if a claw type) with a shifter should be sufficient since it's only 7s.

If that's not it, I'd throw it on a stand or flip it and shift through the gears while manually assisting the derailer's return spring. After perhaps a twiddle on the barrel adjuster, 99% of the time this diagnostic will reveal the cause to be a cable issue, usually excess friction.

Originally Posted by Bill Kapaun View Post
That's a lower level DER on the food chain.
But since 7s is such a reliable standard, you should be able to make any old bit of crap work consistently.
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Old 11-12-13, 10:29 AM
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Originally Posted by Sprayman View Post
I've tried all of your suggestions and all seems to be in order. I'd love to replace the derailleur with a Deore, but that would probably cost more than I paid for the bike.

Then again, having a malfunctioning drivetrain sucks.
So what? You'll have a little more money in the bike but it will be a lot more fun to ride.
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