Forum home Road cycling forum Workshop

Rear mech engaging the smallest sprocket.....

milesemilese Posts: 1,233
edited April 2016 in Workshop
The rear mech on my TT bike doesn’t like to engage the smallest sprocket.

If I shift down the block it will shift smoothly, but then stop on the 12T, rather than the drop down to the 11T. Eventually it will shift, or if you give the mech a little push it will move outwards and shift.

Its like there isn’t enough tension in the spring to pull it all the way over. I’ve lubed and cleaned the mech, spraying loads of GT85 in there. It’s the same irrespective of cable tension.

It’s a Sram Force 10 speed set up.

Any ideas?

Posts

  • keezxkeezx Posts: 1,318
    Friction IN the cables.
    Mech needs adjustment under the 11 sprocket (more to the outside)
  • StillGoingStillGoing Posts: 5,207
    Milese wrote:
    The rear mech on my TT bike doesn’t like to engage the smallest sprocket.

    If I shift down the block it will shift smoothly, but then stop on the 12T, rather than the drop down to the 11T. Eventually it will shift, or if you give the mech a little push it will move outwards and shift.

    Its like there isn’t enough tension in the spring to pull it all the way over. I’ve lubed and cleaned the mech, spraying loads of GT85 in there. It’s the same irrespective of cable tension.

    It’s a Sram Force 10 speed set up.

    Any ideas?

    If you disconnect the cable, will it drop onto the 11 tooth sprocket? If it does, you need to re-index the derailleur. Maybe you pulled the cable too tightly when clamping it to the derailleur?
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • BobbinogsBobbinogs Posts: 4,841
    ...or maybe just as simple as adjusting the limit screw by the odd half turn?
  • milesemilese Posts: 1,233
    Thanks for the replies.

    If I take all the cable tension off with the barrel adjuster, or adjust the limit screw so the mech can move all the way towards the drop out, it is still the same.

    The more I think about it the more I wonder whether it is friction in the cable inner which is greater than the strength of the spring. So even though their is no tension on the cable, the spring still needs to be able to pull the cable through?

    That said, they are fairly new jagwire slick cables and jagwire outers that only get used for racing.

    I'll disconnect the cable and see if it works. Any other ideas?
  • svettysvetty Posts: 1,904
    Bent hanger?
    FFS! Harden up and grow a pair :D
  • gloomyandygloomyandy Posts: 520
    How big is the cable loop that goes from the frame to the rear mech? SRAM mechs seem to be very sensitive to the way the cable runs in this loop. It is very tempting to make it too tight.
  • milesemilese Posts: 1,233
    I think the answer is that 'lubricating' new cables with teflon grease is a bad idea.....

    Thanks for comments.
  • BobbinogsBobbinogs Posts: 4,841
    ah yes, that wouldn't help. On things like that I use multi-oil. Same goes for the brake noodle, the little cable run under the BB, etc.

    Good shout from Keezx.
  • Nick PayneNick Payne Posts: 288
    You could try putting a washer under the derailleur mounting bolt, to move the whole derailleur out a millimetre or so, which means the derailleur parallelogram spring tension will be a bit higher on the smallest cog. You'll also have to adjust the limit screws for the high and low gear and turn the barrel adjuster (or change the clamp point on the cable slightly) so that the derailleur is still centred on the cogs in each gear.
  • sandyballssandyballs Posts: 577
    Nick Payne wrote:
    You could try putting a washer under the derailleur mounting bolt, to move the whole derailleur out a millimetre or so, which means the derailleur parallelogram spring tension will be a bit higher on the smallest cog. You'll also have to adjust the limit screws for the high and low gear and turn the barrel adjuster (or change the clamp point on the cable slightly) so that the derailleur is still centred on the cogs in each gear.

    I would not suggest doing this, it should not have a washer behind and you are simply evading finding the actual cause. Along with this the b-screw is unlikely to get purchase on the stop to enable it to work leading to more problems.

    If after the cable Is removed and hi-low screw wound out it does still not line up I would go with bent mech hanger. Don't just unscrew tension, physically remove the cable so that it is completely ruled out.
  • StillGoingStillGoing Posts: 5,207
    Milese wrote:
    Thanks for the replies.

    If I take all the cable tension off with the barrel adjuster, or adjust the limit screw so the mech can move all the way towards the drop out, it is still the same.

    The more I think about it the more I wonder whether it is friction in the cable inner which is greater than the strength of the spring. So even though their is no tension on the cable, the spring still needs to be able to pull the cable through?

    That said, they are fairly new jagwire slick cables and jagwire outers that only get used for racing.

    I'll disconnect the cable and see if it works. Any other ideas?

    Disconnect the cable completely and see if the derailleur moves to the smallest sprocket. If it does, your indexing was out. If it doesn't, something is sticking on the derailleur.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • ErasmusErasmus Posts: 48
    Shouldn't make any difference with an 11t top sprocket, but have you tried screwing in the B tension screw to push the mech further away from the sprockets? Good luck anyway, John.
Sign In or Register to comment.