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Rear Cassette Skipping on Specific Cogs
I just returned from a long bike tour and, unsurprisingly, found that my chain had worn past the point where it needs to be replaced. Before I began the tour, I installed a brand new drive train, including front chainrings, rear cassette, and new chain. The chain is now worn out now, so I replaced it with a new chain. When I rode the bike again I found that the chain was slipping/skipping on the rear cassette but it seemed to be localized only on one or two of the cogs (#3 and #6 out of 9, incidentally). This too was not too surprising to me since in the past I have worn through cassettes at about the same rate as I wear through chains even if I am being diligent about monitoring chain wear. So I put on a new cassette and take it for another test ride. Again, the chain is skipping, and again it is happening mostly (exclusively, I think) on the #6 cog (I did not notice it happening on #3 after replacement). So this is happening with a combination new chain and new cassette, and seemingly localized to just one or two cogs. To complicate it a bit more, the new cassette is actually a different size (range) than the first, so the "#6" cog on the new cassette is actually a different size than the #6 cog on the old cassette, though not by much (9-speed new 11-25T versus old 11-32T). Any idea what is going on here? Could something not be aligned correctly that just so happens to cause a problem on a specific rear cog? No slipping was observed to occur prior to the new chain, so the old chain and old cassette combination were fine together, though worn.
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First thing I think of is a bad chain link, tight link ot poorly assembled chain. Andy
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While staying on the #6 cog can you get rid of it by turning the barrel adjuster?
John |
Andrew, a bad chain/link is an idea that I had not considered. However, I had every indication that this was a brand new chain when I opened the package and did not notice anything fishy about it when I was handling it before and during installation.
70sSanO, maybe I am not understanding you suggestion properly. The skipping I am referring to is a slipping of the chain on the cassette, perhaps by not engaging properly with the cog/teeth and momentarily loosing contact. Not skipping as in bypassing one of the cogs as I change gears up and down the range (i.e., going from 5 to 7, skipping 6). In the past when I have had this sort of chain slipping problem it happened most readily when I was applying a large torque to the crank and the chain was under tension. Here, however, it seems to be happening even under much more moderate tensions and 'pedaling forces.' |
Which way did you connect the new chain? A quick link or with the Shimano pin that breaks off?
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John's question goes to whether it's a specific cog or all the cogs that seem to skip. My question goes to whether it's not cog wear at all. Big difference in what the answer suggests. Then there's ring wear too... Andy
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Originally Posted by shelbyfv
(Post 22136665)
Which way did you connect the new chain? A quick link or with the Shimano pin that breaks off?
Originally Posted by Andrew R Stewart
(Post 22136670)
John's question goes to whether it's a specific cog or all the cogs that seem to skip. My question goes to whether it's not cog wear at all. Big difference in what the answer suggests. Then there's ring wear too... Andy
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I’m not asking about skipping cogs. If it is off, not enough to shift, but just enough to try and lift and then fall back on the cog, it will look like skipping.
If you are able to turn the barrel adjuster to smooth it out, it opens up a bit of a can of worms. Possibly the hanger, although it is usually at the end, maybe a cable that just happens to stick, shifter, cassette spacing, etc. John Edit added: Since it skipped on #6 (and 3) with the old cassette and chain and it skips on 6 with the new cassette and chain, it might not be the cassette and chain. |
Did you bike fall on the derailleur side on the tour?
John |
Along with the other suggestions did you shorten the new chain since your new cassette has a large cog that is 7 teeth smaller than the old one? Also you may have to adjust the B-tension screw to go along with the new setup.
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Could be a cable needs replacement. If the chain slipped with the old parts and now with the new parts, it's probably not the chain or the cog.
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I checked the derailleur alignment and it was quite poor (bent), and probably has been so for quite a while since I remember no recent events that could have done it. I bent it back to pretty close to straight and not the derailleur is hanging much more aligned with the sprocket that it is supposed to be on. After fixing this I then had to readjust the cable tension to properly index and to shift between each cog, which it seems to be doing well (see caveat below). Throughout all of this, though, the skipping still occurs and only on cog #6.
There is one caveat when it comes to the derailleur cable tension, which relates to John's suggestion of the problem stemming from the chain being at the edge of shifting to the next gear. The skipping only occurs when there is at least moderate tension in the chain (e.g., pedaling under at least some small load and not when pedaling "in the air" on a bike rack). If I am riding down an empty street and watch the cassette carefully while on cog #6, waiting for the skipping to occur, I think that I can see it trying to jump to the next smallest cog (i.e., #7), but it is happening too fast for me to be completely sure that's what's going on. If this is the case then that would lead me to believe that the cable tension is too loose and needs to be tightened. However, adjusting the tension using the barrel adjuster at the handle bars does not seem to affect the skipping and it will still occur regardless of whether I loosen or tighten the cable (even going to an extreme degree where I am no longer properly indexed on the correct numbered cog).
Originally Posted by Crankycrank
(Post 22136996)
Along with the other suggestions did you shorten the new chain since your new cassette has a large cog that is 7 teeth smaller than the old one? Also you may have to adjust the B-tension screw to go along with the new setup.
Originally Posted by 2manybikes
Could be a cable needs replacement.
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If you're checked for a tight link, derailleur misalignment and cable friction, maybe make sure the B-gap is set correctly as Crankycrank mentioned since you've changed cassette range.
https://cimg9.ibsrv.net/gimg/bikefor...777bc76ba2.png I've found that having the wrong spacing here can sometimes cause crappy shifting and/or skipping around in the middle of the cogset; some systems are picky. Manufacturers usually give guidelines but you can always do some fine-tuning on the workstand and while out on a ride to see what works best. |
Originally Posted by SamSam77
(Post 22137544)
I checked the derailleur alignment and it was quite poor (bent), and probably has been so for quite a while since I remember no recent events that could have done it. I bent it back to pretty close to straight and not the derailleur is hanging much more aligned with the sprocket that it is supposed to be on. After fixing this I then had to readjust the cable tension to properly index and to shift between each cog, which it seems to be doing well (see caveat below). Throughout all of this, though, the skipping still occurs and only on cog #6.
There is one caveat when it comes to the derailleur cable tension, which relates to John's suggestion of the problem stemming from the chain being at the edge of shifting to the next gear. The skipping only occurs when there is at least moderate tension in the chain (e.g., pedaling under at least some small load and not when pedaling "in the air" on a bike rack). If I am riding down an empty street and watch the cassette carefully while on cog #6, waiting for the skipping to occur, I think that I can see it trying to jump to the next smallest cog (i.e., #7), but it is happening too fast for me to be completely sure that's what's going on. If this is the case then that would lead me to believe that the cable tension is too loose and needs to be tightened. However, adjusting the tension using the barrel adjuster at the handle bars does not seem to affect the skipping and it will still occur regardless of whether I loosen or tighten the cable (even going to an extreme degree where I am no longer properly indexed on the correct numbered cog). The new chain is the same length (same number of links) as the old chain; I did not change its length. The new cassette range is a subset of the old cassette's range and the cogs I gave up are ones that I basically never used in the old cassette. The B-screw seems to be fine. Is there another way to check if the cable might need to be replaced? |
I am a little uncertain now about what the gap distance should be when the B-screw is properly adjusted. In the graphic provided by hydrocarbon it seems to be 15 mm, whereas I've seen other sources say around 5 or 6 mm. In any case, I adjusted my B-screw over a wide range and it did not seem to affect the skipping problem.
I was able to video the cassette as I rode the bicycle and caught it in action multiple times, in 1/8 slow motion. See video here, https://vimeo.com/574230335 The skips occur around time indices: 9 s, 38 s, 56 s, and 2:01, and are annotated on the video frame. Watching the video makes it clear that there is no jumping up/down the ramp as was hypothesized earlier. |
Find that stiff link... LUBE YOUR CHAIN!
Did you really put on a new cassette.. or was it new/used cassette.... from a friend? |
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