SRAM shifting issues

dhuck88
dhuck88 Posts: 6
edited June 2011 in Workshop
Hi all,

Have recently fitted a new SRAM Apex group to my roadie and Im having trouble with the chain coming off the outside of the top ring.

I have a 50-34t chainset and a 11-23 cassette with a short cage mech, the chain is also new. When I shift into top gear, i.e. 50-11 and put any small amount of pressure on the pedals the chain drops off the outside of the chainring. I have tried all sorts of adjustments with the gears, I've taken a couple of links out of the chain to get the correct length and the tension is about right. I also have a spacer behind the BB cup on the drive side. It feels like a problem with the line of the chain but looking at it it doesnt look like anything out of the ordinary. Possibly a chainring problem?

Any ideas or any similar experiences?

Any advice woud be greatly appreciated.

Thanks

Comments

  • rozzer32
    rozzer32 Posts: 3,923
    Someone will probably be along who will know 100% but I don't think you need the spacer in behind the BB. I think they only supply it for use with MTB.
    ***** Pro Tour Pundit Champion 2020, 2018, 2017 & 2011 *****
  • dhuck88
    dhuck88 Posts: 6
    Cheers, I ran the spacer on my last setup as well though. I didn't have it in originally because I put it on the non drive side by accident and still had the same problem, I think having the spacer in improves the chain line in this case, thanks though!
  • duckson
    duckson Posts: 961
    Assume you have set the FD limit screw?
    Cheers, Stu
  • Pokerface
    Pokerface Posts: 7,960
    duckson wrote:
    Assume you have set the FD limit screw?


    Wot he said.


    Sounds like the limit screw on the front mech is set so that the front mech is moving too far to the right when you shift to the big ring - pulling the chain off the top of the big ring. I've had this problem before.
  • Gazzaputt
    Gazzaputt Posts: 3,227
    You shouldn't need the spacer. As said this is usually for MTB i haven't fitted one to any bike I have ran SRAM on (C'dale, Focus and Canyon)

    I actually say it's a combination of the spacer and the FD limit.
  • keef66
    keef66 Posts: 13,123
    Can you measure the actual chainline? Centre of the seat-tube to the mid point between the 2 chain-rings.
  • satanas
    satanas Posts: 1,303
    First, the spacer probably isn't necessary but is unlikely to be causing the chain to derail unless it's thick enough that it's totally destroying the chainline. (It may make things a bit quieter when on the small ring and the smaller cogs but otherwise shouldn't make much difference.)

    Next, start from scratch. The cage should be 1-3mm above the outer ring at the closest point; 1mm is better.Then, set the angle of the mech such that the outside cage plate is parallel to the outer ring. If the cage is a funny shape then I find it best to set it so that the inside front part of the outer cage plate (next to the chain) is parallel with the chain when in top gear; this may mean that the rear of the cage angles out slightly.

    You should then check the limit screws and cable tension; this has been documented ad nauseum so I won't repeat it here. Keep clearance to a minimum without rubbing. If the chain still persists in coming off it can often help to carefully(!) bend the front of the outer cage plate inwards slightly (1-2mm). Assuming that the frame isn't bent and that there is nothing grossly wrong otherwise then that should do it.

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