Bicycle Mechanics - Rear Derailler pully rubbing against cogset
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I was working on my bike this afternoon to get it ready for the first spring ride tomorrow and I seem to have acquired a slight problem that I can't figure out. The one of the rear derailler pullyies rubs against the cogset when I am on the small chainring. The rubbing is only intense on the cog in the rear, Does anybody know what I can do to try and fix this. I could probably ride the bike without fixing it, but I would like to repair this problem as fast as possible.
03-15-03, 09:36 PM
Yes you need to make a "B" screw adjustment. This is the screw that sets the pitch of the der. body on the der. hanger. Screw it in until the pulley no longer touches the cog.
have you adjusted the b-screw? The B-screw controls the derailleur body angle.
Parktool has a good page on rear derailleur adjustment:
I tried the B screw, I was pretty tight when I started. I unscrwed it all the way and tightened it all the way and nothing changed. Do I need to tighten the wire or something?
03-16-03, 06:43 AM
Is this happening while cross chained in the small cog / small chainring combo?
If the rubbing occurs when the top of the d'rer pulley comes up to the bottom of the cog it could be a result of chain stretch. With the chain under tension, measure the distance from pin to pin across 12 links, this measurement shouldn't exceed 12 1/16". If it's more, time to replace the chain.
From the beginning of the 0th Link to the Beginning to the 12th link is 30.4mm = 11.96" measure from the center of the pins. It seems like its not that, but thanks for the idea!
The problem only happens with the smallest chainring in the front and largest on the back, so no cross chaining.
03-16-03, 08:21 AM
Doesn't seem to have any wear, is it a fairly new chain? Only small ring / large cog, no other cog / ring combination? Axle is fully seated in the drop-outs?
Is the top of pulley making contact with the bottom of cog or are they trying to overlap, say side of pulley to side of cog contact? I was thinking maybe you could try adding a link to the chain, but it would seem the problem would occur in some big ring selections too if that was the cure.
If that doesn't help, stay out of the granny combo and evertything will be fine ;)
Only the one combination, though it seems mighty close on the 2nd largest cog in the rear. I think I might have to just stay out of the granny gear combo. Its really weird because I didn't have this problem at the end of last season.
What happens exactly is that the pulley cog and the cog actually touch tip to tip through the chain because they are so close. So it does not appear to be a side to side type thing.
03-16-03, 09:10 AM
You can always try to take a link out of the chain.
Big question: did you change the casette to one with larger cogs? Does your biggest cog have more teeth than the original?
Sorry to bring this thread form back form the dead but I seem to be having the same problem. The b-screw is all the way in and it still rubs. Would adding a link or removing a link solve the problem? Spire were you able to fix this? thanks
BTW its a sora derailleur.
04-08-05, 07:34 AM
I put a 11 to 34 Cassette on the used bike I was rebuilding for my young grandson. It had a cheap one with only 30 teeth max. The chain hit the 34. No way could I change the angle of the derailleur to correct the problem. The derailleur hanger was just too short for a 34. I found if I centered the chain properly under the cog, the rubbing stopped. However, now the side of the chain hit one of the middle cogs. So I tweaked that noise out and all worked perfectly. My grandson gets good gearing for the mountains where he lives and his dad got a simple way of adjusting the rear derailleur.
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