My Mountain Bike Has This Problem Where When I Try To Pedal It Shifts Gears By Itself,what Can I Do To Fix It?

Your derailleur might need adjusting. It that's the case then read this:http://sheldonbrown.com/derailer-adjustm…
or read Autoshifting:http://sheldonbrown.com/autoshift.html
Sheldon Brown is a master with lots of great advice.
You can take it to a shop if you don't want to try it yourself.

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5 Comments »

  • Rose P said:

    take it to a shop.
    I hope you dont think I was tryna be smart. I wasn’t thats just all I can say

    # 12 February 2010 at 10:45 pm
  • I can only be me said:

    When you are at the shop, make sure that they check that your chain is not stretched out/worn out as well. If it is, no amount of adjusting the cables will do any good. You may need to replace the chain and cassette/freewheel. This is likely if the bike has been ridden a lot of miles or you ride off-road.
    Also, check to see that the derailleur or hanger (where it attaches to the frame) are not bent. This is common if you fall over to the right side!

    # 13 February 2010 at 3:50 am
  • DingleBe said:

    the indexing on one of your derailers needs a tweak, like the guy said a shop shouldnt charge more than 10 bucks maybe to do it.

    # 13 February 2010 at 5:06 am
  • Andrew P said:

    Your shift switcher may be set to switch to another shift.

    # 13 February 2010 at 9:48 am
  • PoKrzyWa said:

    Your cables have probably stretched. This happens with all bikes. The good thing here is that you use the bike enough that it would get to this point.
    Two things you can do:
    1. Take it to a shop. The adjustment shouldn’t cost more than a few bucks.
    2. DIY – shift the rear derailleur to the smallest cog setting. Free the cable by unscrewing the nut or screw holding it to the derailleur. Make sure the plastic wheel on the derailleur is even with the last cog, tighten the cable with pliers or such, and and tighten the cable it back in. There are diagrams at http://www.parktools.com that may help you more than words alone.
    Good luck
    Happy riding

    # 13 February 2010 at 12:33 pm

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