rear mech tension adjustment

formerlyknownasbonj
formerlyknownasbonj Posts: 483
edited May 2010 in Workshop
The rear mech on one of my road bikes has got a slight issue in that to change down, i.e. to go up to a larger cog, the increase in cable tension required is such that I have to move the STI shifter by TWO clicks, i can then click it back one and it will stay on.
So for instance to go from 4 to 3, I have to move the shifter from 4, to 2, to 3 - and the rear mech will just move from 4 to 3.

You might say just increase the tension of the rear mech cable, but if I do that any more then it doesn't change up (i.e. to a smaller/easier cog), in other words it is at the tightest tension it can be without failing to change up on releasing tension.

I have fiddled with the B-tension screw and tried it at the full range of its movement seemingly to no avail, doesn't make it better or worse - seemingly doesn't affect it wherever I have it.

This problem has only come about since I changed to a steel frame with horizontal dropouts. It is a fairly old frame, and it has not got a separate removable mech hanger, the bit the mech bolts onto is just like an extension of the dropout.
The axle sits in the back of the dropouts, but seems to still have the problem if i move it slightly forwards.
I run the STI cables through a downtube cable stop: http://www.sjscycles.co.uk/product-Prob ... -18209.htm but that is benign.

Everything else is 'standard', i.e. I am not using any weirdness, adapters, friggers, kludges or bodges.

The mech is shimano, long cage, I am running 11-23 9 speed cassette with shimano 105 9 speed STIs, triple front rings.

The problem is get-round-able, but annoying. Would bar end or DT shifters help (can they apply a bit more tension before going an extra click than STIs, which is what it seems to require...? )

Comments

  • keef66
    keef66 Posts: 13,123
    I think you need to get an LBS to check the alignment of the mech hanger.
  • oh, what using one of those sticks that pins in it and rotates round like a compass. yeah worth a try i suppose, cheers
  • keef66
    keef66 Posts: 13,123
    Yep, that's the jobbie.

    If the mech hanger isn't the culprit then I might start to suspect the cable, especially the short piece of outer before the rear mech