Chain slipping in a particular gear

sitedrm Posts: 3
edited April 2009 in Workshop
I recently built a bike and installed a 9 speed Shimano cassette. However in 7th gear the chain slips under pressure when pedalling. I can't work out whether it's slipping over the sprocket or if it's attempting to engage on the adjacent sprockets, but it certainly slips when I'm pedalling hard. I'm using friction shifters and I've tried adjusting the position of the derailleur numerous times, and no matter where it is it still happens. All the components are new so it can't be worn teeth or chain, and it only happens in one gear. What are the possible causes of this?

Things that I've considered are the fact that at the moment I've only got a single front chainring and it's rather small at 44 teeth, so I might try a bigger one. On a related note, I was also unsure about the length of the chain. I followed the rule of the smallest size it's possible to fit round the biggest sprocket + 1 link. However the smallest size that was possible was just bigger than one link so I rounded up to the next whole link, then added another link after that. Is it possible I've made the chain too long, and if I had could that possibly cause this problem? Either way, if I do try a larger chainring I'll need to change the chain length anyway.


  • Wappygixer
    Wappygixer Posts: 1,396
    Is your mech hanger bent?
    Is the 7th sprocket OK?Does it have any strange shapes it shouldn't have?
    If it works fine in all other gears I cant see it being chain length and deffinately not chain ring size.
    It has to be something to do with that gear.
  • VinceEager
    VinceEager Posts: 247
    You might try playing with the cable tension - if the cable is too taught, that can lead to the chain jumping around the cassette and sometimes the problem is only evident / worse when in specific gears.
    ...the bicycle is the most efficient machine ever created: Converting calories into gas, a bicycle gets the equivalent of three thousand miles per gallon...
  • synchronicity
    synchronicity Posts: 1,415
    You tend to know if it is trying to engage in another gear (a fair amount of crunching noises) or if the chain is truly slipping on one of the cogs (a single definite... err... clunky noise)