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Sram force rear mech - missing something?

johngtijohngti Posts: 1,971
edited June 2015 in Workshop
Bought a used force 10 speed set up for a cx bike I've built up, set it up according to what I've found on the web and following what I usually do for shimano groups. On the stand, everything is hunky dory, works up and down the cassette. But when I stand to pedal, the mech slips like a drunk with wet feet walking on ice. Doesn't happen with seated pedalling.

Now, it's a used mech, the shifters look like original force 10-speed ones. There is quite a lot of side to side play in the b-bolt - more movement than seems reasonable even when it's firmly attached to the mech hanger. I'm hoping I'm wrong but could this be causing the slippage? Mech just too old and needs replacing maybe? Or - and this is a long shot - is there something different to setting up SRAM compared to shimano that I've missed?

Posts

  • rafletcherrafletcher Posts: 1,235
    If you mean the chain slips on the cassette when you stand up, as opposed to it changing gear as you stand up, then it's usually a worn chain and/or cassette issue. The rear mech has no load placed on it when pedalling normally - the tension is between the chainring and the cassette.
  • johngtijohngti Posts: 1,971
    rafletcher wrote:
    If you mean the chain slips on the cassette when you stand up, as opposed to it changing gear as you stand up, then it's usually a worn chain and/or cassette issue. The rear mech has no load placed on it when pedalling normally - the tension is between the chainring and the cassette.

    No, gear change style. Chain and cassette are both brand new
  • bob6397bob6397 Posts: 218
    Assuming that you have used a 10 speed chain?? 9 or 8 (or less) speed chains are wider and won't sit on the cassette properly.. In the even more unlikely situation that you have used an 11 speed chain, that just won't sit at all as it is thinner again..
    Boardman HT Team - Hardtail
    Rose Pro-SL 2000 - Roadie
  • johngtijohngti Posts: 1,971
    bob6397 wrote:
    Assuming that you have used a 10 speed chain?? 9 or 8 (or less) speed chains are wider and won't sit on the cassette properly.. In the even more unlikely situation that you have used an 11 speed chain, that just won't sit at all as it is thinner again..

    Nope - 10 speed chain. It's got to be the sideways play in the mech.
  • bob6397bob6397 Posts: 218
    And everything (IE mech hanger at both ends) is tight?
    Boardman HT Team - Hardtail
    Rose Pro-SL 2000 - Roadie
  • johngtijohngti Posts: 1,971
    bob6397 wrote:
    And everything (IE mech hanger at both ends) is tight?

    Yep. Even checked the hanger wasn't bent.
  • sungodsungod Posts: 13,882
    There is quite a lot of side to side play in the b-bolt

    side to side suggests it is moving in-out wrt to the plane of the wheel, or wobbling on the pivot, which would be a sign of a badly worn pivot bearing (i.e. a trashed rear mech)

    or do you mean it is rotating around the pivot much too far? sram mechs have a collar with a tab that must seat against the hanger, the b-screw then adjusts distance between the upper wheel and the cassette (i.e. different to shimano) is the tab in the right place?
    my bike - faster than god's and twice as shiny
  • johngtijohngti Posts: 1,971
    sungod wrote:
    There is quite a lot of side to side play in the b-bolt

    side to side suggests it is moving in-out wrt to the plane of the wheel, or wobbling on the pivot, which would be a sign of a badly worn pivot bearing (i.e. a trashed rear mech)

    or do you mean it is rotating around the pivot much too far? sram mechs have a collar with a tab that must seat against the hanger, the b-screw then adjusts distance between the upper wheel and the cassette (i.e. different to shimano) is the tab in the right place?

    It's side to side unfortunately. Don't suppose there's any way to fix it?
  • Ben6899Ben6899 Posts: 9,096
    sungod wrote:
    There is quite a lot of side to side play in the b-bolt

    side to side suggests it is moving in-out wrt to the plane of the wheel, or wobbling on the pivot, which would be a sign of a badly worn pivot bearing (i.e. a trashed rear mech)

    Didn't SRAM modify the pivot design on later rear mechs? Because the initial design was prone to excess wear and premature farm buying?

    Or have I had some kind of highly detailed, cycling mechanics related dream?
    Ben

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  • sungodsungod Posts: 13,882
    johngti wrote:
    It's side to side unfortunately. Don't suppose there's any way to fix it?

    you can disassemble the pivot and see exactly what has happened (if it's like red, there's a fiddly spring clip to remove then comes apart), maybe there's a way to sleeve it or something, or try the lbs bits box for a broken one to scavenge for parts
    my bike - faster than god's and twice as shiny
  • cswitchcswitch Posts: 261
    have you checked the freehub on the rear wheel. If side to side movement there it could be causing the issue. Rear mechs do have a little bit of side to side play anyway but I have no idea how much yours is moving by.
  • johngtijohngti Posts: 1,971
    cswitch wrote:
    have you checked the freehub on the rear wheel. If side to side movement there it could be causing the issue. Rear mechs do have a little bit of side to side play anyway but I have no idea how much yours is moving by.

    I have. No movement. I suppose I was clutching at straws really. When the mech is off the bike, there's probably a good mm at least of play in the joint. I'll have a look at it again tomorrow and if there's nothing to be done I'll probably get an apex mech off wiggle for £26.
  • bazzer2bazzer2 Posts: 189
    I've just installed a force rear mech. It's proper solid. The only side to side movement is about a millimetre where the top jockey wheel has a bit of give in it for the indexing to be quiet.

    Reckon yours is bent.
  • johngtijohngti Posts: 1,971
    bazzer2 wrote:
    I've just installed a force rear mech. It's proper solid. The only side to side movement is about a millimetre where the top jockey wheel has a bit of give in it for the indexing to be quiet.

    Reckon yours is bent.

    I reckon it's trashed. I tried to fix it at the weekend but couldn't get the b-bolt out so have up in the end and ordered a new apex mech. Someone else might have more luck with fixing it, it's for sale in the classifieds now.
  • johngtijohngti Posts: 1,971
    Stuck an apex mech on last night, tried it out today and worked perfectly. Which is nice.
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