Bicycle Mechanics - Jockey Wheel Cage Rubbing against chain making the chain pop
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I picked up a bike at a garage sale a couple of weeks ago and have had so much fun riding it I just now today made time to clean and inspect it thoroughly. In one gear combination, I don't remember which, the cage on the upper jockey wheel of the rear derailler rubs the chain and causes the chain to "pop" and click when it goes past the cage. I can try to get a picture of it if it helps, but I have never seen this before and have no clue what to look for or how to fix it. Any ideas would be greatly appreciated!
Does it happen when the chain is on the small ring and big cog? If so, then you'll need to adjust the B-screw by turning it in until there isn't any "chain rumble" when the crank is turned backwards, in that gear combo. Easiest to do in the stand.
05-20-12, 01:53 PM
05-20-12, 03:24 PM
I don't see how the B tension screw would have any effect on the idler pulley cage rubbing the chain. The cage should always be in a plane parallel to the vertical front to back plane of the bike frame (or freewheel). In that position, with the chain coming directly off the freewheel, there is no gear combination where the the cage would rub anything except the freewheel cogs, in which case b-tension adjustment would be in order.
The only way for the cage to rub on the chain, other than just plain bad tension adjustment, is if the assembly is badly misaligned. That calls for a trip to the shop to check hanger alignment and any possible damage to the derailleur cage.
05-20-12, 03:34 PM
Sounded to me like either the chain was too long and the gear that gave the trouble was small-small (perhaps on a triple with a large tooth spread and a underequipped RD cage). Or an issue with inconsistent cog spacing. Both of these can be remedied in a pinch with a b-bolt.
Agreed on the alignment, sometimes, a bent cage or hanger only acts up in one gear. Especially if we are to take this noise as the chain hunting for the next larger cog.
Either way, I'd start with the b-bolt.
Another and likely possibility is that the upper jockey pulley bearings/bushing may be worn enough to give the pulley too much sideways (lateral) movement, which would allow the chain to move the pulley far enough to the side and allow the derailleur cage to interfere with the chain. That pulley has a small amount of sideplay built in, about 1mm in either direction. If that's the case, it's time for a new pulley.
Think I found it, the derailler shifter tension is allowing it to "half-shift" and get kinda stuck and hunting between shifts and that is when it would rub. It seems to be worse in the small-small combination, so maybe the B tension bolt would help also? I definitely need to adjust the tension so that it can't half shift. The pulley teeth look OK to me, but I am going to get my shop to take a look also.
05-20-12, 10:28 PM
"the derailler shifter tension is allowing it to "half-shift". Follow this procedure from the beginning without skipping any steps, to correctly adjust your derailleur: http://www.parktool.com/blog/repair-help/rear-derailler-adjustments-derailleur
"It seems to be worse in the small-small combination" Do not cross-chain; you have similar, more efficient gear combinations available which will be quieter and not wear the drivetrain as much.
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