I just replaced my front cogs and back sprockets with new ones (I didn't use a torque tool or replace the chain). I also replaced the sealed bearing bottom bracket on my pedals. The old bearings were 115 mm long and the new one is 117,5 mm long.

Now I feel some sort of vibration, and there is a noise like the gear wants to change, but the rear derailleur is set correctly with one click per gear. What can cause vibration and noise from the chain?

  • Every bike shop and proper tech I've spoken to about drive trains says to replace warn cogs/rings and a chain at the same time because of the wear patterns.
    – Jack M.
    Sep 2, 2012 at 19:06
  • @JackM. But he replaced the chain 50KM before replacing the cogs. Not nearly enough time for the chain to "take a set". Sep 3, 2012 at 12:22
  • 1
    My money is on misadjusted derailers. Sep 3, 2012 at 12:24

3 Answers 3


If you changed the crank length then the front derailer likely needs to be adjusted, and the rear may need a few tweaks. Also, when you change the rear cluster there can be a difference of a mm or two between old cluster and new, requiring adjustment of the rear derailer.

Have you readjusted both derailers "by the book"?

(Whether or not you used a torque wrench would have little bearing on this issue, though you need to be sure to check that your crank bolts are tight every 200km or so for the next 1000km.)


Was the reason for the gear change because they were worn? If they were worn the chain most likely is also worn unless it was changed recently. The general rule with chains is to replace it when the cassette is changed. As the chain wears it gets longer and won't match your cassette. Your old chain wore as the old cassette wore so they matched. Slide the chain off the crank and spin it by hand just to verify that it spins easily, this will rule out a bad bearing (sometimes new isn't perfect).

  • Before I changed the sprockets and cogs. I did changed the chain. That showed me that my old sprokets were worn. I wrote the bike in that condition for about 50 km. And then I cleanded the chain thoroughly. That's when I changed the rest of the parts. Menaing the sprockets, cogs and bearings in the pedals.
    – Airis
    Sep 2, 2012 at 11:00
  • So I just got my bike from my local mechanic. Turns out that the centre bearings were bad. Even though I just both a brand new one. He just changed that part and everything was alright. Look like new is not always perfect.
    – Airis
    Sep 7, 2012 at 12:35

a. sorry for my limited English cycling jargon

b. by absence of a chain tool, I too replaced my cogs but not the chain. And was surprised by the rattling sound.

c. Everyone tells me to replace both at the same time. That got me thinking: why?

The chain will wear (cfr. wikipedia). The links will slack. As a result, with new sprockets, the shackles will be 'squeezed' together to match the sprocket teeth. Once a link leaves the sprocket, it will be allowed to stretch away to it's full length.

This will cause a rattling of the same frequency as when it 'tries to shift gears'.

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