chain jumps at jockey wheel - but only on smallest rear cog

[BigonaBianchi]

Chain is jumping (one 'click') at the jockey wheel but it only happens on the smallest rear cog, the rest are fine.
I checked cable tension, derailer shifts to each cog correctly in turn, checked limit screws front and back derailers both set correctly. Mystified I took off the chain an dgave it a really good clean and checked for stiff links, all well on the chain front however. So I took off the cassette (shimano ultegra 6800 11 speed) gave it a proper clean and re assembled it having checked each cog and spaces for visable damage. I re assembled it all and the chain still jumps just one click/skip on the small cog only on each pass of the chain.

I'm stumped, any ideas?

Cheers.

 

[lpretro1]

Checked for bent hanger?

 

[User6179]

I had a lock ring washer on my bike and when I changed cassette from a 12t to 11t bottom cog the chain caught the washer making it jump , took me a while to notice what had been happening .

 

[BigonaBianchi]

Tha hanger looks straight to me....the lock ring ...hmm...I have changed it recently as I stupidly threaded it on tightening too much last time i cleaned the cassette...still a 12t though....maybe thats it..i'll take a closer look and pull it apart again if necessary...cheers

 

[Ajax Bay]

+1 to Eddy's lock ring size check.

Otherwise: You'll be in the large chainwheel when this occurs so (in that large-small (correct) configuration) the jockey wheel will be vertically well clear of the smallest sprocket.

Or: Is the small sprocket an original with the cassette or is it an incomer, perhaps, and has been subject to many more km of wear (unlikely for a small sprocket even then)?

 

[Colin_P]

I'd say a stiff link although you have already checked for that.

 

[BigonaBianchi]

I'd say a stiff link although you have already checked for that.

yeah that was my initial thought as well but the chain is clean well lubed and every link is free...my money is on the lock ring...sounds aboiut the only thing left i didnt check yet...

 

[Ajax Bay]

He has indeed.

I took off the chain an dgave (sic) it a really good clean and checked for stiff links

If it was a stiff link you'd likely see it on at least the adjacent sprocket.

 

[Racing roadkill]

I've encountered this when one or both jockey wheels have worked loose. Also when I've changed to a new chain, on an old cassette. I find the best thing to do, is just get a new pair of Jockey wheels, only use a new cassette, when fitting a new chain ( it doesn't matter so much if you use a new cassette, with the existing chain). And check the alignment of the hanger ( I've not had problems with polymer hangers, just metal hangers). The jockey wheels only cost a couple of quid, I find it's worth changing them with every chain / cassette change.

 

[Colin_P]

He has indeed.


If it was a stiff link you'd likely see it on at least the adjacent sprocket.

Unless of course that link only gets stiff at a certain (tighter) bending radius.

Unlikely but possible.

 

[Ajax Bay]

In what way is it "worth changing them with every chain / cassette change"? What is the 'business case' for this frequency? Why not more often? Or less often? To what extent does the performance of jockey wheels deteriorate? How do you measure this? Or is this just your arbitrary rule of thumb? Do you change brake cables when the blocks need replacing?

 

[robjh]

the chain still jumps just one click/skip on the small cog only on each pass of the chain.

Not quite sure what you mean by this. If it happens once per revolution of the chain then it has to be chain-related, once per rev of the small sprocket then related to the sprocket, ditto if once per rev of the jockey wheel.

 

[Ajax Bay]

link only gets stiff at a certain (tighter) bending radius

Assuming this is the step from 11 to 12, the difference in radius is only 9%.
Should have said: "see it at least occasionally, on at least the adjacent sprocket"

 

[Colin_P]

Assuming this is the step from 11 to 12, the difference in radius is only 9%.
Should have said: "see it at least occasionally, on at least the adjacent sprocket"

It is a tricky one to diagnose from behind a screen.

If the bike were in front of me, I'd flex the chain back and forth against the rivets (as you do) on the section which is causing the jump. (assumes the jump happens at the same chain location each time).

 

[wam68]

Had the exact problem a while ago. Solution was I had put a spacer on before the lock ring. Don't ask how that happened. Must have been pissed. Anyway it messed the gearing as the chain on the small ring was resting on the spacer and not the sprocket. Once removed the syncing was perfect