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  1. #1
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    Grinding and Skipping

    Hi guys. I have a 2012 Trek Superfly 100 AL Pro 29er. From the day I took it from the Bike Shop I have had issues with the shifting. The original issue was on the front derailer it wouldnt shift from the small cog to the large cog without alot of skipping if it switched at all. I brought it to my LBS twice and had a mobile bike mechanic try to fix it but to no avail each time. Finally, the LBS found there was something wrong with the actual shifter, and made other adjustments and it shifts well now..

    However, this fix seems to have come at the expense of the rear shifting. While it may be coincidental, after getting the bike back it has been making grinding/crunching noises from the rear derailer and skipping gears when it is in the higher gears (easier to pedal gears). (It seems to just actually jump and want to skip, but not actually skip) It does not matter which cog the front derailer is on. It does it on the last 4 or 5 cogs on the way up to the highest gear.

    I'd really like to address this issue myself and avoid more trips to my LBS as I live wuite far from there. Plus I would really like to learn how to maintain my own bike moving forward so this is a good start.

    Any ideas? Thanks in advance.

  2. #2
    Ski N Bike Tech
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    http://www.parktool.com/

    That will help you learn how to work on bikes.

    As to what's happening, it sounds like the cables have settled in and just need some more tension added.

    All you need to do is turn the barrel adjuster at the shifter till it shifts from the smallest cog onto the second from the smallest cog. Once it's on that cog, continue to make small turns to the adjuster until it no longer makes any grinding. Then shift through the gears slowly making sure it goes to all the gears without any issues.

    I just woke up and am typing this on my phone. Hope it help.

  3. #3
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    Thanks for the reply. Not exactly following though..lol.. It already shifts to the smallest and second smallest cog. so are you saying to put it in the second smallest cog on rear, and then make small turns to the barrel adjuster and test each gear? Right now it will only grind at the last few cogs on the cassette.

    So which way do I turn the barrel adjuster as I go up the cassette testing each gear? Towards me or away from me (If I am on bike)

    Thanks again!

  4. #4
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    Sometimes a rear derailleur may shift cleanly through part of the range but not all of it, so it might shift OK in the smaller cogs but not in the larger ones. Most likely you need to add a bit of cable tension so try a turn or so counterclockwise and see if that helps. It is possible that the shop made an improper adjustment so there could be too much tension, but I doubt it.

    Like Skinbike said start inn the smallest rear cog and shift up 1 gear. If it does that cleanly then shift back down again- it should not hesitate. If this is good you may have a different problem.

  5. #5
    Ski N Bike Tech
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    Quote Originally Posted by daspin View Post
    so are you saying to put it in the second smallest cog on rear, and then make small turns to the barrel adjuster and test each gear? Right now it will only grind at the last few cogs on the cassette.
    Yes

    [QUOTE/]So which way do I turn the barrel adjuster as I go up the cassette testing each gear? Towards me or away from me (If I am on bike)[/QUOTE]

    Doing it on the bike, you would turn away from you. You want to increase the cable tension.

    When you can, you will want to invest in a repair stand. Also, see if any of your local bike shops teach any classes on basic maintenance. It's a good jump off point for the at home mechanic. It help shorten the learning curve.

  6. #6
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    THANKS GUYS! I'll try it out! And yes, I will be getting a bike stand. I also was thinking of sending out a message to our club memebers to see if there was anyone interested in a bike maintenance clinic and then trying to organize one with a couple good bike techs.. I know I would be interested so I'm sure others would be as well, and everyone could pay a fee to pay for techs time..

  7. #7
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    You can also get the symptoms you described from a misaligned derailleur hanger. If you look from the rear of the bike it might be obvious that the hanger is bent. My bike shop charges $12 for a hanger realignment.

  8. #8
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    I just changed my rear cable, set it up on my stand, thought I had it right, went out for a ride and it was doing exactly the same thing, skipping on the larger rear rings, added some tension on the cable and it cleared right up.

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