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  1. #1
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    Gears skipping on descent?

    All,

    I am having problems with my gears skipping while I am descending.

    Here is the background:

    I ride an Ibis Mojo SL with a 140mm X-fusion shock, 1x10 set-up, MRP chainguide and tensioner, SRAM XO med cage derailleur, SRAM 10spd chain and shifter.

    I live in Arizona and the terrain is super chunky. I find that when I descend at speed (25mph+) and go to pedal for more speed, my gears skip. Any ideas?

  2. #2
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    skip, like broken freehub? or changes gears

  3. #3
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    Changes gears. Its kind of exciting but not the good kind of exciting.

  4. #4
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    It's possible that you have a small amount of play in your hub or pivot bearings and under the right forces the angle of the hub/cassette changes just enough to cause the chain to slip to the next ring.

  5. #5
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    Cable routing/cable too short. Those are often the culprits for ghost-shifting.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  6. #6
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    Exactly which gears are skipping? Is the chain dropping from the 2nd smallest gear to the smallest gear when you hit bumps?

  7. #7
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    Its funny you mention this, I have been hearing some squeaking recently from the near the pivots. I am going to tear my bike apart on Wed. I let you know what I find.

  8. #8
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    Yes, jumping between the smallest and second smallest. Truth be told, I am guessing at this one as I am looking forward at that speed vs. at the gears. However, I am in the smallest gear when it happens. I dont think it is the cabling/ routing as I have a little extra slack in the line but I will check that as well.

  9. #9
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    I recommend double checking the limit screw and chain length. I think a too-loose chain or too-tight limit screw would cause what you are describing.

  10. #10
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    Quote Originally Posted by btablak View Post
    Yes, jumping between the smallest and second smallest. Truth be told, I am guessing at this one as I am looking forward at that speed vs. at the gears. However, I am in the smallest gear when it happens. I dont think it is the cabling/ routing as I have a little extra slack in the line but I will check that as well.
    Do the highest gears shift ok on the work stand?

  11. #11
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    The guide (upper) pulley is pretty far away from the smallest cogs in a wide (like 11-36T) cassette, and so little problems might be exaggerated. It shifts perfectly under load on a smooth road sprint, same speed, same gears?

    A medium-cage derailleur doesn't offer quite the tension a short cage would, but of course a lot of 1xs are made out of the stock 2x parts cause giving up a $$$$ RD and buying a new one is impractical.

    1) slightly bent derailleur hanger + imperfect high limit (these often go together)
    2) pedaling hard into chunk over 25 mph. Slow down?

  12. #12
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    Gears skipping on descent?

    I say hanger is bent . It don't take much. Put the bike in stand drop the chain into smallest gear stand in back of the bike and pedal while looking between the chain/gear and hanger , shine a light from under if needed and see if the gap stays the same . If it looks fine , try turning your adjuster barrel. Good luck


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  13. #13
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    Quote Originally Posted by btablak View Post
    Yes, jumping between the smallest and second smallest. Truth be told, I am guessing at this one as I am looking forward at that speed vs. at the gears. However, I am in the smallest gear when it happens. I dont think it is the cabling/ routing as I have a little extra slack in the line but I will check that as well.
    Check everything the other posters mention and take a look at your chain wear and cassette wear as well. I had a worn cassette that would jump from the second smallest to the smallest under power when going down hill. The chain would slip out of the teeth on the second smallest gear and the tension of the derailleur would pull it down to the first. It would also slip in the smallest cog too. The smallest cogs don't have as many teeth in the chain as the bigger ones do and will be one of the first places that lets you know your cassette is worn. Hope its something easier and less expensive than this.
    Narrow is the path to life, few are those who find it.

  14. #14
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    Check your b screw on the rear derailleur. It could be too far away from the cassette.

  15. #15
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    ^^^ i bet ya thats it.

  16. #16
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    Quick Update - I checked the hanger and it was not bent. Good news. I also checked the chain, cog, and chain ring for wear and they all looked good. Again, Good news. I checked the rear triangle - and it was loose. Not too bad but enough. I tightened it up and have *less* skipping. I am working on the bike this weekend and will check the b-screw. Thank you all for the ideas!

  17. #17
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    3rd on the b-tension being too tight as that won't wrap as much chain around the smaller cogs and chain can skip to the smallest cog! LOOSEN the b-tension adjuster screw.

    Have FUN!

    G MAN
    Last edited by Gman086; 04-13-2015 at 06:32 PM.
    "There's two shuttles, one to the top and one to the hospital" I LOVE this place!!!

  18. #18
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    its a ****ty tune job on a bike that loves to throw chains

  19. #19
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    I thought I was the only person in the world with this problem... riding flat out down hill over lots of small rocks and corrugations (enough to shake your fillings loose) and having the chain continually jump from the smallest cog to the 2nd smallest and back again until the trail smooths out. Very annoying to say the least.

    The bike is a Pivot Mach 5.7c (with Shimano XTR Shadow+ 2x10) and the problem has been there since day one when I bought the bike brand new. Chains, cassettes, chain rings and rear derailleur have all been replaced when they've worn out or broken, but the problem won't go away. Hanger is straight (verified with a DAG-2), the rd is resting on the high limit screw (no cable tension) when in top gear, all gears shift smoothly without fuss and the cable outers don't appear to be too short, although how do you tell?

    So why the annoying skipping over the bumpy stuff?

    I've asked this same question a year-or-so ago on the Pivot forum here, but apart from discovering that the hanger was slightly bent, no suggestions made managed to fix the problem. So I've just learned to live with it and just curse Pivot every time it occurs. I'm willing to bet that it has something to do with the dw-link suspension just shaking the proverbial crap out of the rd (maybe the rear triangle could be loose...it certainly feels tight, must check again) because no other dual suspension bike I've owned has had this problem, and nobody else I know has either. Naturally the LBS has no idea.

    Can anyone think of a fix?

    Thanks in advance,

    R.

  20. #20
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    Re-read my earlier post. What a lot of novice bike mechanics don't get is that the B-tension STIFFENS when you weight the bike on some suspensions - especially VPP and DW link. There's no need to "live with it"... trust me!

    Have FUN!

    G MAN
    "There's two shuttles, one to the top and one to the hospital" I LOVE this place!!!

  21. #21
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    G MAN,

    Thanks for the quick reply.

    The B-tension screw is the one that moves the jockey wheels up and down relative to the cassette... correct? If so, are you saying the jockey wheel should be closer or further away from the cassette?

    R.

  22. #22
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    Quote Originally Posted by Pinchflat66 View Post
    G MAN,

    Thanks for the quick reply.

    The B-tension screw is the one that moves the jockey wheels up and down relative to the cassette... correct? If so, are you saying the jockey wheel should be closer or further away from the cassette?

    R.
    He did say loosen in 2013, but I think he meant farther away from the cassette.

  23. #23
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    If there is no obvious wear and tear issues, then I'd guess the derailleur needs tuning.

    If it's only happening on the outermost gears, I'd start with the limit screws. If it's happening between the two smallest gears, give the top limit screw a counter clockwise quarter turn. If it's happening between the two largest gears, give the lower screw a counter clockwise quarter turn.

  24. #24
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    Quote Originally Posted by ColinL View Post
    He did say loosen in 2013, but I think he meant farther away from the cassette.
    Loosening the screw (turning counter clockwise) moves the jockey wheel closer to the cassette, so I think that's what G MAN means. Isn't it?????

    Not having much time after work, I quickly "loosened" the b-screw a couple of turns before a ride last night, and, whilst the skipping still occurred on the badly corrugated stuff, it was nowhere near as bad as normal. Will need to check in daylight tomorrow to see how close the jockey wheel is to the cassette with me sitting on the bike and adjust the clearance accordingly.

    Will then try giving the top limit screw a quarter turn counter clockwise and report back what happens.

    So how far away from the large cog on the cassette should the upper jockey wheel be set to? I've read on various web sites anything from 3mm to 10mm, but I guess it's a matter of just seeing what works.

    R.

  25. #25
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    only adjust one thing at a time so you can rule out the possibilities. keep adjusting the b. i don't go by how far the jockey is away from the cassette, but how much wrap is on the sprocket. my chain falls off the 11t sprocket at the 6-7 o'clock position. my measurement from jockey to sprocket is about 15mm, so don't go by measurement

  26. #26
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    Loosening the screw is correct so you are setting the pulley closer to the cassette. B-tension is tricky on some full suspension designs because it changes when you sag the bike. Trick I do is let most of the air out of rear shock and then sag bike to mfgr recommendation (25% for my Bronson). Shock will stay put and then I check the pulley distance and adjust to the low end of the range. If I were you, just keep loosening her until the prob goes away.

    Have FUN!

    G MAN
    "There's two shuttles, one to the top and one to the hospital" I LOVE this place!!!

  27. #27
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    I work at a bike shop on Saturdays. the is plethora of small things that cause hiccups in drive train. heres where I would start. how old is your chain? do you have a chain gage. how old is your chainrings and cassette. is your 13t cog a common cog for your riding? check for elongated grooves between teeth on the cassette, check for any twisted links in the chain..... check your chain wrap in all gears....while also checking for appropriate chain length. check your derailler hanger isn't cambered in any way. make sure the derailleur cage isn't twisted, any one of these can make for funny little issues.

  28. #28
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    Quote Originally Posted by Gman086 View Post
    ... let most of the air out of rear shock and then sag bike to mfgr recommendation....
    Brilliant! Why didn't I think of that??

  29. #29
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    Quote Originally Posted by akiracornell View Post
    ... how old is your chain? ... how old is your chainrings and cassette...
    This problem has happened since the bike was brand new and is still occurring even with virtually all of the drivetrain having been replaced after wearing out. And yes, the hanger is straight. So the problem isn't there...it's somewhere in the adjustment of the rd. So I'll keep loosening the b-screw for now.

    But thanks for your suggestions.

    I've also read somewhere that the length of the cable outer between the front and rear triangles can upset things with the rd, but I don't believe that's the problem here because the skipping doesn't happen on big hits, just on lots of bone-shaking little ones.

    R.

  30. #30
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    typically when adjusting the screw that affects how the chain wraps the cassette, you only let it out far enough to where the upper pulley on the derailleur doesnt ride up against the largest cog. in theory at 25% sag on a dw link the chain should be lengthened a tid, taking up some slack and pulling on the derailleur cage causing the chain to further wrap the cassette. you just don't want so much wrap the upper pulley is riding the big cog.

  31. #31
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    btw what cassette are you running? are you running an expander kit 40-42? or 11/36? I ask because if your chain has room to get rid of some links you can get better wrap on the small cogs with a shorter chain and also increase tension. especially if you have a medium cage, and you only have 11/36.

  32. #32
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    Quote Originally Posted by akiracornell View Post
    ... what cassette are you running? ...
    It's got a 11-36 cassette, 26 & 38 tooth chain rings and a long cage. I've checked the chain length before (by letting all the air out of the shock, big chain ring and big cog) and I can't go any shorter.

  33. #33
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    Back to basics. Is the shifter cable a bit too short? If so, adjust at the shifter or buy a new cable.
    Are you running a chain made for a different number of rear cogs, or should I say did they sell you a bike with a chain mismatched to the cluster?

  34. #34
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    Quote Originally Posted by Ridnparadise View Post
    ... shifter cable a bit too short? ... chain made for a different number of rear cogs...
    No, cable is slack when derailleur is sitting on the limit screw.
    No, the 3 or 4 chains that I've used and worn out on this bike have been the correct type for the cassette (10x).

    Took it for a ride this morning...still skipping. Shall loosen the b-screw a bit more.

    R.

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