chain length and B Screw adjustment

marcusww

I have been having rear shifting issues with Ultegra 6700 setup. I found the outer cable entering the rear mech was frayed causing 'springyness' in the outer. As you can imagine over 50 miles on Sunday I ended riding it like a fixie!. Replaced all the outers and inners now. BUT..........

When trying to move the mech / top jockey wheel closer to the cassette with the 'B' screw I found that I could not get the top jockey wheel to touch the cassette biggest sprocket (11-28T) when unscrewing the B screw all the way out. - (I wanted to do this to get a datum of adjustment) The chain was renewed about 500 miles ago. There was no scientific method of chain length measurement when renewed.

Does the shortening or lengthening of the chain let the rear mech move closer to the cassette?

drlodge

Marcusww wrote:

Does the shortening or lengthening of the chain let the rear mech move closer to the cassette?

Yes, with a shorter chain (e.g. chain on big chain ring), the RD is "pulled" forward and so will also be further away from the cassette. Try removing the chain from the chainrings completely, so the chain is slack, and see how the RD moves backwards and up.

marcusww

Thanks, does that mean I need to take some links out of my chain?

drlodge

Marcusww wrote:

Thanks, does that mean I need to take some links out of my chain?

No, why would it? I'm not sure the top jockey wheels need to get up close to the biggest sprocket. If your gear changes are smooth and positive, then there's no problem.

FWIW, the way I setup my RD is to take off the chain, then rotate the RD by hand so the top jockey wheel touches the sprocket, I can then see precisely what the alignment is and adjust as necessary. With the chain back on, the jockey wheels won't be touching the cassette as the chain tension pulls them away. Its not a problem.

Is your RD jockey wheel closer to the cassette when in the smaller chain ring than when in the larger one?

marcusww

I checked again and the top jockey wheel after undoing the b screw almost all the way - it is close to the big cassette cog - say about 5mm away - when in small front and big rear. All seems OK now.

If I undo the B screw all the way, the jockey and top cog still do not touch which is good and gear changing is fine - If this B screw is undone all the way does this effect anything else in the setup?