Loose rear mech cable

Manc33
Manc33 Posts: 2,157
edited January 2014 in Workshop
On my shifters now, I click to change from the 11T to the 12T and the rear mech won't change. I do another click and it changes to the sprocket after the 12T, I click downshift and it goes to the 12T.

I know to tighten the cable so it changes from 11T to 12T on the first click but then, there's no way it will change from the 32T (biggest) to the next one down, I have to screw in the barrel adjuster and of course doing that, means it won't change from the 11T to the 12T again!

It seems there is nothing on the gear shifter between the shifter itself and the cable housing, it kinda just bends where it goes in the shifter because of it. Its not the shifters that are going wrong it is the fact that theres nothing "supporting" the cable where it meets the shifter. Then again its exactly like that on the left shifter and, no problems. Perhaps a new barrel adjuster is needed.

Or would it work if I held the cable housing straight and tightened the cable a bit? No because it just won't change onto the 11T then.

B-tension screw is all the way in, or could it be because that is all the way in? Shimano Alivio rear mech can handle up to 34T and I have it all the way in on a 32T. :oops:

I am going back to STi shifters soon but still need these working for my MTB lol. It has to be that B-tension screw, although why a mech cares about having 32 or 34 when its changing on the 12T and 11T I have no idea.

Comments

  • dj58
    dj58 Posts: 2,221
    What bike is it, drop bar road or flat bar hybrid? What shifters are they?
  • Manc33
    Manc33 Posts: 2,157
    Flat bar. Old XTR M951 shifters (8sp), PG850 cassette 11-32T, PC850 chain, Alivio rear mech.

    I am changing my cables and shifters soon anyway so I scored/cut a groove in the cable with it on the 11T (using a knife and using the metal thing on the frame the cable housing goes in as a guide) then clicked it and cut a groove... all the way to lowest gear. From the 11T to 12T aka the first click, about 1mm of cable comes through. Next click is 3mm and all subsequent clicks are 3mm or, about.

    I don't know if that first click is taking up a 2mm slack and only pulling 1mm through, or the shifter has mechanically had it.

    I can see exactly why it is doing it, but don't know how to stop that slack happening when the cable is fully released on the 11T. The normal thing to do would be click the shifter from 11T to 12T, it won't change, so just wind out the barrel adjuster on the rear mech until it changes up, but I have to wind it out loads (to take up the 2mm slack lol) then the 32T to 26T shift is way out.

    It is loose here when the cable is fully released:

    n9OaUvn.png

    Loose at the shifter/adjuster on the end of the barrel adjuster nearest the shifter. Like the first click just takes up the slack from it. :|
  • gozzy
    gozzy Posts: 640
    Make sure the cables are pulled through tight before you attach them and follow this video for rear indexing.
    And don't worry about how much cable length the shifters are pulling through, that's for Shimano's engineers to be concerned about.

    http://www.youtube.com/watch?v=SkzvfCaIbyQ
  • Manc33
    Manc33 Posts: 2,157
    Gozzy wrote:
    Make sure the cables are pulled through tight before you attach them and follow this video for rear indexing.
    And don't worry about how much cable length the shifters are pulling through, that's for Shimano's engineers to be concerned about.

    http://www.youtube.com/watch?v=SkzvfCaIbyQ

    I'm not an engineer but I know it isn't right. :P

    Don't need to see the video :lol: I have setup umpteen bikes with rear mechs over the years and never seen this happen.

    Is there a difference between winding out the barrel adjuster on the shifter/mech once its setup, and getting the cable tight to start with and winding the adjuster a tiny bit? I can't see any difference. Once its tight enough, the shifter can't make it looser.
  • gozzy
    gozzy Posts: 640
    Always wind the barrel adjuster all the way in before set up, then use it to adjust cable tension once you've connected the cable.

    You may have set up millions of bikes, but it sounds like your doing something wrong somewhere, so it may not hurt to spend 5 minutes of your time watching a video. Or if you must, continue to be stubborn and spend hours messing about with it.
  • dj58
    dj58 Posts: 2,221
    How old is the rear derailleur? Might be a combination of wear in the shifters and derailleur that is causing the problem. Are you sure that the nipple on the cable is located correctly in the shifter housing? Have you loosened the cable clamp bolt at the RD and tried taking up the excess slack before re-indexing the gears?

    I have just had a similar problem with my nephew's MTB STI 7 Speed Altus 14-34 mega range. Could not get it to index correctly, turned out to be excessive wear in the long cage pivots of the RD. plus the fact that the replaceable aluminium rear drop out was bent out of alignment. New parts solved the problem, STI shifters and cables were fine.
  • gozzy
    gozzy Posts: 640
    Manc33 wrote:

    It is loose here when the cable is fully released:

    n9OaUvn.png
    |

    I suspect you shouldn't have loose cable like that at the shifter. Which probably means you've either not pulled the cable through properly and/or your outer isn't seated properly.
  • Manc33
    Manc33 Posts: 2,157
    Kink in the cable housing under battery pack, gone unnoticed. :oops:

    Now the shifters are off the bike with cable still in, the first click is an equal length of cable to the rest. I didn't think an XTR shifter would develop a mechanical fault.

    I wasn't trying to be an ass, but I knew that video didn't answer why it won't change from 11T to 12T. I mean I could have followed it all etc but it just tells you initial setup, does he mention kinks in the housing? I bet not. :lol: