Chain slack on small chainring.

bilsea159
bilsea159 Posts: 256
edited October 2010 in Workshop
My chain goes slack when dropping down to the small chain ring and moving down the cassette. Chain is new and has right number of links in it. I suspect the rear derailier is at fault as I get no problems in the large chainring, so is it possible the spring on the rear mech is the culprit and the rear mech is not springing back when changing gear, I can get the tension of the chain right by pulling back on it slightly?

Comments

  • keef66
    keef66 Posts: 13,123
    Are you sure the chain's the right length? Which method did you use to determine this?
  • bilsea159
    bilsea159 Posts: 256
    Chain is right length as it has been alright for 4 months so I am misleading a little to say it is new.
  • keef66
    keef66 Posts: 13,123
    In that case it sounds like your assumption is correct in that the rear mech is at fault. Springs do break, but you should whip the thing off and give it a damn good clean first. I have seen rear mechs with restricted movement because of a small stone jammed in the parallelogram; the same could conceivably apply to the fore / aft movement of the cage.

    If the spring is indeed broken you should be able to get a replacement.
  • Pokerface
    Pokerface Posts: 7,960
    There's also a screw on the rear mech that you can use to essentially tighten the chain tension.


    However, if the problem occurred out of the blue, then something must have broken, unless you got some massive chain stretch in 4 months (which is unlikely but possible)
  • bilsea159
    bilsea159 Posts: 256
    New rear mech was the answer, thanks for the replies.
  • keef66
    keef66 Posts: 13,123
    Did you just go for the simplest solution, or was the thing knackered beyond repair? (I know Shimano spares can sometimes be a nightmare to get hold of)
  • bilsea159
    bilsea159 Posts: 256
    I did go for the simple solution although the spring in the mech was still intact, but I bought the rear mech second hand so could not vouch for how old or how servicable it was