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Rear Mech Problem.

NodnolNodnol Posts: 168
edited February 2009 in MTB workshop & tech
It's a Sram X.9 Medium Cage (2008) rear mech, and I'm having issues with it when it comes to shifting down to the smallest sprocket (or highest gear). Now at first, I loosened the tension from the shifters, adjusted the H and L screws, and still the smallest sprocket was unaccessible.

I took the cable routing off, and allowed the chain and mech to access the smallest sprocket, made slight adjustments, then put the cabling back. Shifts up fine, but wont shift back down all the way.

I've tried retensioning the cable from the mech end, undoing the screw, pulling the cable through and then re-tightening, adjusting the H and L screws to near perfection, adjusting the tensioner at the shifter end and now it seems to just be getting worse! It sits on the biggest sprocket fine, but I get loud "clunk" when shifting up, only for the mech to hardly move, and it's only when I shift up again that the chain drops down to the second biggest sprocket.

It shifts fine all the way down to about the fourth smallest sprocket, then simply wont go any further. There's no slack in the cable, and no give in the shifter. And yes, I've cleaned the cables and made sure there's no mud stuck inside the cabling that might be causing a blockage etc.

This has already thrown a spanner in todays ride, I've been itching to get out but I've been on a tight time scale! Not very happy, but would appreciate anyone's help!

Cheers guys.

Posts

  • Andy BAndy B Posts: 8,115
    Could be the mech pivots need a little light lube, or maybe a fresh cable (I know you've cleaned it, but sometimes a fresh one works better than a cleaned one.)
    2385861000_d125abe796_m.jpg
  • is the b-tension screw screwed in enough?
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    Resident Grumpy Smurf
  • zariszaris Posts: 337
    I took the cable routing off

    That's might be why! The cable housing usually gives that exra little cable i think for it to be tensioned right...

    if not try following the Shimano XTR set up...always works for me :)
    http://www.youtube.com/watch?v=Z3bVgP_M ... re=related

    Loving the deep voice guy hahaha!! xD

    zaris
  • NodnolNodnol Posts: 168
    I'll give it a look over, however when I take the cable routing off and allow the mech to change through it changes down to the smallest sprocket. If the pivots were stiff, surely it wouldn't drop to the smallest sprockets? It's only upon fixing the cabling back into place that it won't shift all the way again.

    One thing I did try was to retightening the cable by placing the mech on the biggest sprocket, and pulling the cable through taught. I might try and put the gear in the lowest, or second lowest, sprocket and try slackening the cable off slightly to see if I develope a bit more play in the mech.
  • you are useing a sram shifter right?
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    Resident Grumpy Smurf
  • NodnolNodnol Posts: 168
    Yeah, X-7. The set-ups what I bought the bike with, and the bike's only six months old, so I was thinking that maybe the cable has worn from use, and would need re-tightening. Never that simple hey? I've tried nearly everything I know to try, and I'm just running out of ideas.
  • jaysonjayson Posts: 4,606
    This sounds to me like a typical sticky old cable problem.

    U say it will shift to the smallest sprocket when u disconnect the cable but it wont when u reconnect it, it sounds like u should just ditch the old cable and housing and replace it with a fresh new one and ur problem should be solved instantly.
  • Andy BAndy B Posts: 8,115
    Without the cable attached set the L & H limit screws.

    Then drop the mech into 9th (smallest sprocket on cassette), reattach cable.

    Gears should now work with minimal fettling of the barrel adjuster on the shifter.
    2385861000_d125abe796_m.jpg
  • NodnolNodnol Posts: 168
    Right just back from tinkering outside, problem all sorted. I ensured the H and L's were correct, took the cabling off and let the chain and mech slip into the smallest sprocket, again checking the H and L's. Pulled the cable through as tight as I could without the mech moving, fettled a little on the barrel adjuster to fine tune and it's shifting perfectly, through all the gears.

    Cheers for the advice guys. When I was pulling the cable through, I frayed it slightly. It hasn't reach the point where the cable is attached to the mech, and I've replaced the cable end and squeezed it tight with a pair of pliers. I'll keep an eye on the cable and see if it frays much more with use. When I'm at my LBS next, I'll pick up a new cable.
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