Hi – thanks in advance for help. I'm relatively experienced with basic bike maintenance, but I've never seen anything like this: on my newish bike, when I am not pedalling, the chain starts to bounce around, with the rear derailleur swinging back and forth. If I back pedal, the rear derailleur also gets a bit jumpy and stuck. What might cause this? B screw? bent derailleur?
My chain is flying around when not pedalling – what could be wrong?
byu/domini_taylor inbikewrench
by domini_taylor
6 Comments
Your freehub/freewheel probably needs replacing or at least servicing. It’s not spinning as freely as it should to help keep tension on the chain.
It can be caused by a sticky freewheel. If it’s not fully free spinning the the chain jumps around like this. I’ve also had similar when my axle snapped. Wheel rolled surprisingly well but a small amount of binding made the chain jump.
Freehub. Pull it, clean it and grease it and see if it gets better. Look online for specs for your FH if you are going to do it yourself. There are plenty of YT videos on how to do this.
I wouldn’t ride it until you do this. This is one of those things that can cause larger problems with your bike.
No tension in chain – derailleur or freewheel.
Freehub needs servicing or replacing.
Are you sure chain is correct length? It’s likely a freewheel or derailleur issue but if you or the last person to work on it just eyeballed the chain then it may be too long.