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  1. #1
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    diagnosis tips please

    I am working on my brothers bike (it is a specialized hardrock...not sure what year.) I replaced front cranks (which included the chain rings...2 piece set) due to some severe bending in the chain rings and replaced the chain too since I wasn't confident that the chain rings didn't damage it. Anyways, everything seemed to go great...indexed well and felt really smooth. Then I took it on a little ride and things still felt great...until I shifted into the highest gear on the rear cassette. Under load, there seems to be a skip, but I can't replicate it on a stand...only while riding it. The problem is I can't see what is happening...if it is the cog or if it is the derailleurs in the back. I suppose if one had the gear they could mount a camera on the back but I don't really want to invest in that a one time fix it project. Any tips on how I could better diagnose this? (I did try to gently apply the break on the stand, but it was torquing pretty hard on it and I don't want to break my stand either.) Any thoughts would be appreciated, thanks!

    P.S., I am really thankful for all of you who are willing to share your experience and wisdom with us rookie mechanics.

  2. #2
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    You may have to set up the rear D from scratch. There are numerous YouTubes on that, though you may be familiar.
    Also, since you replaced the chain, it may be that the cassette had been badly worn. If that's the case, a new cassette is in order. Sometimes when a drive train is badly worn, everything has to be replaced.

  3. #3
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    Just want to clarify, you're saying it's skipping under load only when the chain is on the smallest cog (highest gear) in the back? No skipping in other gears at all? And there's definitely a skip where the pedals lunge forward under load and then catch again as the chain reseats on the cassette?

    You also want to make sure you're not just experiencing the chain rubbing the front derailleur and making a grinding/metal rubbing sound...this often happens on the extreme ends of the gear range, but wouldn't produce a chain skip symptom.

    I'd guess either worn cassette or you're H limit screw needs to be adjusted...maybe need to adjust rear derailleur cable tension as well, but seems less likely if skip symptom is isolated and only happens the highest gear. If other gears are shifting smoothly without skips, the derailleur cable tension is likely fine.

  4. #4
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    Skip as in chain is jumping a tooth? other wise known as a knee VS bar smasher?

    OR is it just skipping a little bit as in not quite tuned right & chain chatter noise?
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  5. #5
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    Skipping under load is almost surely due to the cassette, very common. Replacing it will solve your problem.
    I brake for stinkbugs

  6. #6
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    Quote Originally Posted by justin70 View Post
    Just want to clarify, you're saying it's skipping under load only when the chain is on the smallest cog (highest gear) in the back? No skipping in other gears at all? And there's definitely a skip where the pedals lunge forward under load and then catch again as the chain reseats on the cassette?

    You also want to make sure you're not just experiencing the chain rubbing the front derailleur and making a grinding/metal rubbing sound...this often happens on the extreme ends of the gear range, but wouldn't produce a chain skip symptom.

    I'd guess either worn cassette or you're H limit screw needs to be adjusted...maybe need to adjust rear derailleur cable tension as well, but seems less likely if skip symptom is isolated and only happens the highest gear. If other gears are shifting smoothly without skips, the derailleur cable tension is likely fine.
    Justin70, yes, that is what I am saying. Every other gear of the rear cassette works splendidly and I know it isn't rubbing from the front derailleur. While pedaling, the peddle seems to hop an eight of a turn or so. Visually, the cassette looks fine and I would doubt that the high gear would have been used as much as the other gears based on how my brother rides. I will look into the h limit screw although I would have thought that would have a similar effect as the front derailleur's limit screws which would impact shifting with other gears as well. If I could observe what is happening, I would have a better idea...but it is the lack of being able to reproduce it on the stand that makes this so puzzling. Thanks for the thoughts though.

  7. #7
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    I don't think it is jumping a tooth...I was looking like an idiot riding around the street with my head down as much as possible to try to see the rear gears...haha. But while doing that, I didn't see any hopping in the chain. It made a metalic pop kind of sound almost like it was trying to move down up a gear and then falling back down, but I didn't see that kind of movement in the chain from what I saw while riding...which isn't the greatest vantage point.

  8. #8
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    Thanks for the response. I hesitate just replacing the cassette only because I want to avoid unnecessary costs with the bike. Everything seems to be working great except this one point. It still is ride-able in this condition, just slightly annoying.

  9. #9
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    Quote Originally Posted by yoyojordo View Post
    Thanks for the response. I hesitate just replacing the cassette only because I want to avoid unnecessary costs with the bike. Everything seems to be working great except this one point. It still is ride-able in this condition, just slightly annoying.
    This is a classic case of a new chain on a worn out cassette, itís not an unnecessary cost, itís your only option

  10. #10
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    If you don't replace the cassette, you'll likely trash the chain....then the front chainrings. Then you get to start from scratch. Replace the cassette.

  11. #11
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    Agree, new chain with old cassette often don't jive. After all, the chain may have been replaced once or twice but never the cassette. At some point they don't like to work together. Put the old chain back on, bet this particular issue goes away.

    (be sure the indexing/H limit screw(s) are set properly and the cable/housings are not causing cable to stick)

  12. #12
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    Yup... had similar situation when my cassette (rear gears) wore out. If you look real close at the teeth on the largest gear you will see that instead of looking like peaks they look more like shark fins. This is due to the excessive wear that a stretched out or worn chain will cause on the cassette rings just like with the front rings.

    Time for a new cassette.

  13. #13
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    I had a similar issue,but was related to play in the derailleur. The first time I had it the derailleur connection to the hanger was loose and under torque the derailleur would wobble causing the skip. The second time I had a similar issue the bearings on my pulley wheels on the derailleur were toast. Under power the pulley wheel would wobble causing a skip.

  14. #14
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    Had a similar situation with an HG800 11 speed Shimano cassette. It would do this on the 3rd gear, the 27t. I ignored it for a few rides, but it didn't go away. Eventually irritated, I stopped on the trail, hooked the saddle over a branch, and spun the cranks slowly while eyeballing it. I eyeballed and eyeballed it. Had a drink of water and did a little more eyeballing. It appeared, in just that spot, that the teeth were a little closer to the 30t than the other teeth. Pulled out the Leatherman pliers and gave it a little tweak. Nailed it. Never had a problem since.

  15. #15
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    I would be inclined to agree with a new cassette, but the largest cog on cassettes aren't (imo) usually the ones to wear out. Usually the middle cogs get much more worn. My advice (in no particular order, but maybe put old chain back on first):
    1. check rear deraileur alignment, clean rear der, check der hanger, make sure everything is tight.
    2. install new shifter cable for rear der, this means you'll have to reset the shifting.
    3. check freehub (put cassette on freehub, try to see if there is a wiggle)
    4. Check wheel bearings and quick release. tighted it all down, try to wiggle hub in frame
    5. check frame, see if there are any cracks in the downtube, chainstay, seatstsys
    6. make sure all chainring bolts are tights and chainrings don't move
    7. make sure cranks and bottom bracket are on tight and spaced correctly
    8. put old chain back on, verify that issue goes away, if it does not, follow rest of steps.
    9. clean cassette thoroughly
    10. if all else fails, take bike to shop, replicate issue, see what they say.

  16. #16
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    Quote Originally Posted by yoyojordo View Post
    I don't think it is jumping a tooth...I was looking like an idiot riding around the street with my head down as much as possible to try to see the rear gears...haha. But while doing that, I didn't see any hopping in the chain. It made a metalic pop kind of sound almost like it was trying to move down up a gear and then falling back down, but I didn't see that kind of movement in the chain from what I saw while riding...which isn't the greatest vantage point.
    Before replacing the cassette ($$$) I would check adjustment. If it is trying to jump up from the smallest gear to the next bigger diameter gear and back down it could be that your stop needs to be adjusted out a bit more, or that the cable needs a bit more adjustment or even replacement. I would verify what is happening during the skip before replacing anything else, otherwise you are just blindly replacing things. Eventually you will see it happen and know what needs to be done.

    Sometimes it is easy to tell if it is jumping up by pushing the shifter button a tiny bit (to go onto larger diameter gear) if it jumps right up when you barely push it then your cable is a little bit too tight and you can usually adjust that out at the shifter adjustment. If that is happening then it could be your cause.

    I would also check that when you shift onto the smallest gear that the cable is releasing the derailleur fully. If there is drag somewhere in the cable you will be able to pull the derailleur cable out manually a little more than it came on its own when it's on the smallest dia. cog. You should not have to pull it out. It should have no drag and be able to come out on it's own.

    Hope this all makes sense

  17. #17
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    If it hasn't been resolved -consider it a necessary fix more than "it is rideable in this condition". As soon as the skip occurs and rider has an accident, it is no longer acceptable.

    Would you, yourself, climb a hill and stand and pedal and want to slip? Think of the consequence.

  18. #18
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    Fixed

    Thanks again for the thoughts everyone. I did end up replacing the rear cassette. It wasn't as pricey as I thought and was a quick fix for the issue. Plus, I got to use my chain whip so that was fun. I never was able to localize the issue while just observing, but with everything working properly now I doubt that the issue was anything related to cable tension, limits, b-screw adjustments or the likes of that. End result...now working smoother than my personal ride. Thanks again and enjoy the trails.

  19. #19
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    Quote Originally Posted by dompedro3 View Post
    Tthe largest cog on cassettes aren't (imo) usually the ones to wear out. Usually the middle cogs get much more worn.

    I think with 1x now it actually is the largest cog wearing the fastest - consider a number that accurately portrays frequency of use, force applied and angle of chainline... I think you'd find the largest cog is getting the highest value if such a number existed.


    Quote Originally Posted by yoyojordo View Post
    Thanks again for the thoughts everyone. I did end up replacing the rear cassette. It wasn't as pricey as I thought and was a quick fix for the issue. Plus, I got to use my chain whip so that was fun. I never was able to localize the issue while just observing, but with everything working properly now I doubt that the issue was anything related to cable tension, limits, b-screw adjustments or the likes of that. End result...now working smoother than my personal ride. Thanks again and enjoy the trails.
    Definitely was just a worn cassette then.

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