Gears Jumping while pedaling

Discussion in 'Mountain Bikes' started by BackTrail, May 15, 2010.

  1. BackTrail

    BackTrail New Member

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    My Specialized Hardrock sport '08 hardtail has problems when i ride.

    When i start off I need to give a little force into my pedals, the chain and whole mechanism seems to "Jump" and it usually makes me fall forward as the pedals stop.

    This happens in all gears on my Specialized and if i pedal fast It jumps too, my bike also makes a constant clicking sound when i pedal.

    What could possibly be wrong with it and would a tune up fix this?
     
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  2. hotdiggity

    hotdiggity New Member

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    Know the feeling - needs a service or the chainwheel or cassette is worn. Chain wear could be another factor too. Another rare cause is a worn/faulty freewheel mechanism. I replaced a whole drive chain once because of a jumping chain only to discover it was the freewheel.
     
  3. john gault

    john gault New Member

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    Does it have the original chain and rear cassette? Do you know how much mileage you have on both?

    Look at your rear cassette and see how many teeth are sharp as opposed to having a squared-off appearance. When they look sharpened that means you are well beyond a worn out cassette. For comparison you can look at the teeth of a new cog at your local bike shop.

    Sometimes you can change the chain and will cause the problems you describe, this is because the chain has worn to the wear pattern of the rear cassette. Personnally (and this is kind of a hot-button issue) I change my chain and cassette at the same time, but a lot of people go thru about 2 (or sometimes more) chains per rear cassette change-out. I can get several thousand miles on a chain and rear cassette.

    I keep a log on my computer (Word Document) and record everytime I replace a major component -- record date and mileage. This way I get an idea of about how many miles I can go with a chain and cog. Very helpful when I go on tour to see if I should first replace a chain or wait until after the trip.
     
  4. john gault

    john gault New Member

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    P.S. If your rear cassette has sharpened teeth and needs replacement I would recommend also replacing the chain, unless you just bought the chain and it has virtually no miles on it, but make sure the chain is compatible with the cassette.
     
  5. hotdiggity

    hotdiggity New Member

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    Does the same apply for the chainwheel then?
     
  6. alfeng

    alfeng Well-Known Member

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    Yes, if the teeth on your chainwheel(s) have been sharpened to a point then they are due for replacment.
     
  7. john gault

    john gault New Member

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    If by chainwheel you mean chainring Crankset - Wikipedia, the free encyclopedia, then NO, it does not apply in the same sense.

    I have to claim ignorance on chainrings; I've never had to replace one -- always bought a new bike before the chainring wore out. My current bike has over 15,000 miles and still has the original chainring. So maybe I try and wear it out to see what the symptoms are and what a worn out chainring looks like compared to a new one. (It's kind of like the age-old question: "How many licks does it take to get to the center of a lollipop?" Personally, I don't know, I've always got impatient and just bit into it.):D

    Here's Sheldon Brown's website and he talks a little about chainrings. Sheldon Brown's Bicycle Glossary Ch
     
  8. Trek43K

    Trek43K New Member

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    Not to get off-topic, but I was going to start a new thread regarding this same subject... However, my bike is basically brand new and it has this same issue. If the bike (2010 trek 4300 disk) is in 2nd gear on the front derailleur and 2nd on the rear derailleur, then it will jump out of gear and go directly to 3rd on the rear derailleur.

    It's not too bad on flat ground but as soon as I go up hill, it jumps out of 2nd into 3rd. I am assuming my problem is in the rear derailleur? How do I go about fixing this issue? Thanks in advance!!!
     
  9. hotdiggity

    hotdiggity New Member

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    Sounds more like a gear tuning issue if the bike's new. If the force of going uphill is just enough to somehow tighten the cable so it jumps up into third, then maybe you should try loosen off the cable tension ever so slightly - say, a quarter turn. Use the barrel adjuster on the rear derailleur and it should be clockwise (I think - so it moves away from the derailleur body).
     
  10. john gault

    john gault New Member

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    Lot to learn here: Harris Cyclery Articles about Gears
     
  11. biclo

    biclo New Member

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    I have exactly the same issue as Trek43K on my new raleigh mojave 2.0 It doesnot jump into another gear, but sounds and move like jumping, only it falls back on the same. I would describe it pretty much as you have done. Certainly I will go soon to its first service, but I want to learn as much as I can to at least be able to get a good decent service.
     
  12. ritadawn85

    ritadawn85 New Member

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    Hi guys, my mates call me speedy, I'm into trials, mountain biking & downhill mainly but love all kinds of bikes..
     
  13. dero

    dero New Member

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    In the case of new bikes, this can be blamed on cable stretches and or chain stretch, your new bike was tunned at assembly and with all the jumping and jarring on the trail your new cables will stretch. If you bought your bike from a reputable LBS they will retune your bike at no charge, the wrench twisters expects this to happen.
     
  14. swampy1970

    swampy1970 Well-Known Member

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    It's probably just a cable adjustment that's required.

    http://bike.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50rparsys-0019-downloadFile.html/13)%20Rear%20Derailleur%20Installation.pdf

    Goto straight to step 5: SIS adjustment.
     
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