Bigger cassette rubbing

CEscorcio

Hello,

I have changed my rear Ultegra Shimano cassette from a 11-25 to a 11-28, the chainset 53-36 to a 50-34 and a new chain. Everytime i put the lowest gear (large cog) in the rear some noise just start to appear like something is rubbing against this cog. Is it possible to do anything to tune it? I already change the High and Low but nothing happens that can help me.

Thanks for the help

sungod

you probably need to adjust the rear mech

if it's shimano, go here...

http://techdocs.shimano.com/techdocs/index.jsp

...in the road section, look for the correct model of rear mech, click on the SI-whatever link for that model, follow the instructions, including those for correct chain length

with your new set-up the capacity increases to 33 and the max sprocket to 28, also check the specification (in the si- document) to see if the rear mech is actually rated to work with those figures, if it was marginal before then it might now be a touch too much

Tom Butcher

Is this a job for the B screw ? If you look at the rear mech as well as the limit screws you should have another screw underneath somewhere - try adjusting that - it should move the mech clear of the big sprocket.

smidsy

Yes B screw is the likely answer. It basically moves the top jockey wheel in relation to the cassette so you can adjust the amount of clearance.

It is the third screw (not the H or L) and pushes against the mech hanger to act against the spring in the parallelogram.

You should adjust so you have about 1 1/2 to 2 links clear space.

CEscorcio

Thanks for the help ,the sound improved a lot but something is still rubbing and i have reach the limit of the B-Screw?

Maybe the Rear Derailleur it´s just too short or it´s already wear and i should change it? It´s a new cassette and chain.

Thanks

smidsy

What rear mech is it.

They have a maximum tooth size depending on the model. It may be that your large sprocket is simply too big.

Shimano Tech Docs website lists all you need to know.

markos1963

If you have adjusted your B screw and it's still rubbing then it's either you have run out of capacity or the chain is too short. You can usually go to a 28T low gear as long as you lengthen the chain enough, too short and it pulls on the mech making it catch on the gear.

CEscorcio

According to the tech docs my rear 6600 the largaste sprocket is 27T and now i have 28T. My old cassette was 25T, I will need to buy a new rear derailleur the 6700

Thanks all for the help.

fossyant

Try a longer chain first

Monty Dog

If you didn't add a link or two to your chain then it's likely to be the problem. Fitted 12-28 cassettes to Ultegra no problems. Unless chain was in good conditionor recent, I'd fit a new chain when replacing cassettes

CEscorcio

Putting 2 links wasn´t enough, had to change the rear derailleur.
Thanks all for the help