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Lower jockey wheel skipping on chain

Posted: Wed Apr 09, 2014 1:13 pm
by snailmale
Hi there,

My lower jockey wheel (aluminium) is skipping on the chain when I run low gears (39-28). It meshes nicely with the outer link of the chain since it is wider, but makes the chain jump a little to the side in order to fit into the inner link. This basically means that the jockey wheel is further inboard (toward the wheel) than the chain when running low gears. There is also noticeably more noise when running on the low gears than high gears, due to the chain rubbing on the jockey wheel. The derailleur itself does not move due to the skipping, but when turning the crank at a very low speed (or moving the chain by hand), I can see the chain shifting sideways slightly to accommodate the jockey wheel when it reaches the narrower chain link.

I have aligned by Low derailleur screw as far outboard, away from the wheel, as possible, to the point just before the chain wants to skip to the 2nd gear. However, the issue has persisted.

Running a Token tiramic jockey wheel on Shimano 105 5700 drive train. I noticed this issue before, but just figured it was normal as my gears shift smoothly. Then I had a chain break, twist and jam inside the jockey wheel cage on Sunday, and I'm kind of paranoid now. After fitting the new chain, I took it in to the bike shop nearby and the mechanic rode the bike up and down a small hill and said that everything seemed A-okay, shifting well. He suggested that I don't waste money by sending it in for a full tuneup.

My guess now is that it is due to a slightly bent derailleur hanger. I'm not fussed by the noise, but do worry that my chain will experience wear and break easily. Should I send it in for straightening, or just ride on? Anyone with advice/experience on this? Thanks!

Re: Lower jockey wheel skipping on chain

Posted: Fri Apr 11, 2014 6:25 am
by veloflyte
It is most likely because the pulley cage is not perfectly aligned with the chainwheel. You can bend the pulley cage a bit to put it in a better alignment. I've done it hundreds of times over the years when I was a bicycle mechanic at the Wheelsmith.

Of course you won't be able to do this if you have a carbon fiber pulley cage.

Re: Lower jockey wheel skipping on chain

Posted: Fri Apr 11, 2014 8:31 am
by bikerjulio
I'm thinking @velo has the most likely answer. ie cage is bent. Sometimes it's easier to remove the RD to eyeball alignment of the pulleys.

2nd thing is as you have already raised - the hanger. And it's true to say that a lot of hangers are not straight.

It needs to be checked with the proper tool. My only caution here is that some hangers don't take well to "adjustment". The metal is often a brittle alloy that can be weakened by the process.

Re: Lower jockey wheel skipping on chain

Posted: Fri Apr 11, 2014 8:33 am
by bura
I would check the hanger and the cage .
The hanger has to be checked very carefully .If there is a slight bend in it I would not use it any further. It may be fine for another 1000kms or more but
due permanent stress cracks can occur in the alloy and all of the sudden you will have a rear derailleur jam bending the rd into the rear wheel which is not good for your health and resulting damage will cost you more than just a new hanger.
If the hanger is aligned perfectly which can be measured very easily (check youtube) then you should check the 105's alloy cage if its bent.
I would dismount the cage to bend it back to its original position.
If there is still some pulley centering needed after all bending and rd adjustment for sure you can center both pulleys different in your cage by using washers if only one pulley needs to be centered some different than the other.