Front derailleur cable tension

liversedge
liversedge Posts: 1,003
edited February 2009 in Workshop
My front D cable snapped in the lever recently and had it replaced at the LBS. When I got it home I found the shift into large chainring was non-existent so I got tweaking. I've also lowered the D because I have compacts cranks (didn't move the D down when I moved from a std crankset). I have tweaked high/lows on front and rear D and got everything super smooth.

BUT

The tension on the front D cable is pretty high when I'm in the large CR and when I drop back to the small CR I get a reall loud clonk/clack. I'm worried that the high tension will make the cable snap sooner than it should. Or maybe its always been high and this caused the cable to snap previously. But I'm sure it wasn't this stiff before.

I've tried loosening the tension but I've found that any lower than it is now and the cage doesn't move across far enough. The front D is in good condition and doesn't seem any stiffer than the D on my other bikes, when I pull it across by hand. But shifting is definitely harder than on my other bikes, takes a bit of muscle to move across from the shifters. Its all 7800 dura ace kit.

Any advice?
--
Obsessed is just a word elephants use to describe the dedicated. http://markliversedge.blogspot.com

Comments

  • careful
    careful Posts: 720
    The tension in the front changer comes from the spring return rather than the cable. Check that the down shifter has no more clicks when the changer is correctly aligned on the inner ring. The cable should be just tight enough so that movement of the up-shift is immediate (ie no slackness in the cable). There is nothing more you can do about the tension. Make sure cables are correctly routed and that the top limit is not set slightly too far in. It could be that when you change to the big ring you are forcing against the limit stop.
    Check also that you got the height right (ie cage clears the outer ring by 1-2 mm. This is most easily done with the chain off if you have a removable link. Hope this makes sense.
  • John.T
    John.T Posts: 3,698
    Almost certain you have the mech hard against the limit screw when on the big ring. Either back of the cable adjuster a bit or the limit screw. Just make sure you can not over shift. My mechs drop back about 2mm when I release the lever.
  • John.T wrote:
    Almost certain you have the mech hard against the limit screw when on the big ring. Either back of the cable adjuster a bit or the limit screw. Just make sure you can not over shift. My mechs drop back about 2mm when I release the lever.

    +1
    I would guess that the "H" limit screw is too tight. This may just allow you to reach the big ring but will spring back when the lever is released. Undo it a quarter of a turn or so.
  • Check your limits, the large clunk on coming down is probably the mech hitting the frame, wind in the low stop a bit to eliminate and wind out the high as above to lower the tension in the outer ring.

    Be aware the mech has a really stiff spring (try turning it by hand, or getting your finger trapped in it) so the tension in the outer ring will always be pretty high.