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  1. #1
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    RFX drivetrain skipping ?

    Bulit up an 08' RFX @ the beginning of the season. The drivetrain was a transplant from a Blur LT - XT cassette, XT 760 crankset, XTR shifters, new Avid cables, XT Shadow rear derailleur, Sram front der., Shimano chain, King HD rear hub, MRP LRP guide w/ Heim bracket. Shifting is flawless, climbing under load is no issue. If I stand and hammer @ the beginning of a descent / run it feels like it skips / pops . I noticed this about mid season on a really fast descent that requires pedalling on a bumpy flatter section. Not quite sure if bumps are absolutly required on just suspension movement but on flats if I stand and hammer there is no issue only descending. The drivetrain looks fine, I replace my chain every season, the crankset and rear derailleur were new for the RFX. The King hub was used and only on the RFX. Any thoughts ? Thanx

  2. #2
    Bite Me.
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    sounds like the suspension is activating the RD - try cleaning up the housing and cables to remove any friction, if that fails, maybe adjusting the housing length between the top tube stop and the seat stay stop, if that fails maybe a bigger cable loop at the rear derailleur (this can be an issue on Shimano stuff, not on SRAM).
    When I see an adult on a bicycle, I do not despair for the future of the human race. ~H.G. Wells

  3. #3
    keholio
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    This sounds too familiar. I finally picked-up one of those handy chain measuring tools because it is always makes the process of elimination easier. If it is not the chain take a good look at the cassette.

  4. #4
    Elitest thrill junkie
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    Quote Originally Posted by keen
    I replace my chain every season,
    I wish I could get away with replacing the chain only once a season.

    How old is the cassette?
    "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

    You're turning black metallic.

  5. #5
    VooDoo user.
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    Sounds like the whole DT is smoked. I'd replace all rings/the chain/ and the cassette. If its still happening I'd dig into the freehub body. How old is the King hub? Have you ever serviced it?

    Reason behind replacing all the DT at the same time is so it all meshes together and you get the maximum lifespan out of the components.

    If you just replace the chain and keep using worn rings and a cassette the chance of chain suck increases and you'll likely shorten the lifespan of the chain ending up right where you are now only quicker. Either that or it will just break.

    Good luck.

  6. #6
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    I'm with Jayem - how old is the cassette? I can usually get 3 chains per cassette. I go through 2 chains per year and change the middle ring once per year. I only change the cassette when it starts skipping just like you described.

    Easiest method, get a whole new drivetrain like timber says. Put on the new chain and replace the cassette and try it. If that doesn't work, add the new middle ring. If its not the problem, you will eventually need these parts anyways so its no loss.

    Also, you can check chain wear by measuring 12 links. New, 12 links = 12 inches. When its 12 and 1/16", replace the chain.

    Mike

  7. #7
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    Cables seem fine no ghost shifting and I can cycle the suspension going along the trail and nothing happens. The crankset is only a few months old and the rear der. was installed new for the RFX. I can only guess and say the cassette has a few hundred miles ??? It doesn't have any visual wear on the teeth but @ the moment it looks like I should try a chain and be prepared for a cassette. I pulled the King's axle and shot a smidge of lube per King's instructions, if I had the $ tool I would have gone farther. I have ridden worn drivetrains that chain suck & shift poorly but mine feels so good except for the mashing on descents.

  8. #8
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    keen,
    Your problem may have one of four sources:
    1. worn off drivetrain, but possibly that's not a case. You write, that it's just couple of hundreds miles old.
    2. dirty cables, but that would cause poor shifting all the time, so my guess - that's not the case.
    3. too long or too short cables can cause ghost shifting. Check the link below - this lenght should be OK
    Pack setup database

    4. CK hub bearings are dirty (bearings !, not a RingDrive problem, but since You'll have the hub opened, You should clean/regrease RingDrive as well)

    How to verify ?

    Put Your bike on a stand, shift to heaviest gear (biggest chainring front, smallest rear), give it a good spin, and while the wheel is spinning try to pedal backwards. If Your drivetrain will start skipping - You have Your answer. If everything works smoothly - that's not a hub problem.

    So if it's my case, how to solve the problem ?

    Open the hub, take of snap ring and rubber seal from the bearing, clean it with WD-40, regrease ( CK RingDrive lube is recommended, but I also used Manitou PrepM with very good results). Put the seal and snap ring back. Repeat for the second bearing. Shouldn't take more than 20 minutes.

    Good luck, serhij

  9. #9
    Never enough time to ride
    Reputation: squish's Avatar
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    Keen, I had a this exact same issue late last summer on the same frame. It would work just fine on level ground or climbing, but as soon as the trail pointed down and got a little rough it was skip city.

    I had a couple of issues going on, but I narrowed most of the issue down to a run of cable housing that was too short, specifically the one between the top tube and the shock stay. The other contributing issue was a slopped out XT Shadow, was some what disappointed with that as the derailleur was only 8 months old! (Shimano took very good care of me on this one, but I'm still contemplating dropping it and going back to SRAM)

    I would start with a fresh rear der cable and housing set. I'd stick up a shot of the cable routing on my beast but it's currently torn down being prepped for some paint work. Maybe Cactuscorn can pop off one of his and post it up.

    happy trails...

    squish
    Get out and ride!

  10. #10
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    [QUOTE=squish]Keen, I had a this exact same issue late last summer on the same frame. It would work just fine on level ground or climbing, but as soon as the trail pointed down and got a little rough it was skip city.

    I had a couple of issues going on, but I narrowed most of the issue down to a run of cable housing that was too short, specifically the one between the top tube and the shock stay. The other contributing issue was a slopped out XT Shadow, was some what disappointed with that as the derailleur was only 8 months old! (Shimano took very good care of me on this one, but I'm still contemplating dropping it and going back to SRAM)

    I would start with a fresh rear der cable and housing set. I'd stick up a shot of the cable routing on my beast but it's currently torn down being prepped for some paint work. Maybe Cactuscorn can pop off one of his and post it up.

    happy trails...


    I did a new chain and went over the drivetrian w/ a fine tooth comb. Pretty sure the problem is related to the shadow rear derailleur. Though the der. is only a few months old it flexs a whole lot. My older XT der. did a lot of flopping (B spring design) but it was always solid. I really like that the Shadow has a positive B stop but not if it sacrifices performance. How did Shimano handle the warranty ?

  11. #11
    Never enough time to ride
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    Mine had a lot of side to side play in it after that relatively short amount of time and it was definitely effecting performance.

    I called Shimano up, they gave me an RA# and off it went. It took about 2 weeks to get it back, not bad considering I'm a 4 day ship point from California.

    happy trails...

    squish
    Get out and ride!

  12. #12
    Natl. Champ DH Poser/Hack
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    ask and.....
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    Last edited by cactuscorn; 01-26-2009 at 06:58 AM.
    No, I'm NOT back!

  13. #13
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    i had that pop/skip feel when i mashed on the pedals. turns out the cassette was worn, replaced it and it went away.

  14. #14
    Roy
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    Get the Hammerschwantz; it will solve all of your problems and you'll be the BMOC around here.

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