Upper Jockey Wheel Rubbing On Biggest Sprocket

ThanksBye

A friends Got a Dura Ace 7800 Short cage rear Mech, and a 12-25 cassette and when in the 25th tooth the Jockey wheel rubs on the cassette, according to the shimano tech docs you should be able to use a 25th cassette.

What can i do to stop this rubbing?

Many thanks

Jon

peddlefever

There is something called a B screw on the rear mech which moves the mech front to back, therefore moving the jockey wheel closer or farther from the cassette. It is the screw nearest to the mech hanger that pushes against it. Screwing it in or out will change its distance to the hanger and move the mech itself.

I hope that helps, although my description is a bit rough as it is a bit difficult to just explain in words without being able to point at the mech.

ThanksBye

Thanks, we've tried adjusting that buy it seems to still rub

sungod

this is in the small chainring?

if it's in the large, might be the chain is a bit short, although its better not to cross chain

try following the rear mech adjustment from scratch...

http://techdocs.shimano.com/media/techd ... 612494.pdf

peddlefever

Strange. I'm not sure what the biggest cog a short cage DuraAce rear mech can handle is, but I would think it could handle a 25 tooth cog, but perhaps that would be the max.

ThanksBye

In Small Chain ring, shiftings perfect been checked over by Mecahnic, just cant stop it rubbing

Monty Dog

DuraAce rear should handle a 28 sprocket - B screw adjustment or chain length would be where I'd start