derailleur catching rear cog

dnrc

Hi all, i have a small issue with my last build.

it's a campagnolo groupset with double front and 9 speed rear.

everything is pretty good and the gears all run smoothly and shift well. Except that when in the 8th cog at the back (second largest) the top of the mech cage kinda drags along the biggest cog.

strangely this only happens when in the smaller chainring, when on the 53 it's OK.

everything else is fine with it.

Any ideas?

ynyswen24

has it got a small screw just below the bolt onto the frame? This would pres against a tab on the dropout just below where the mech bolts in. Screw this in a bit at a time to increase the chain gap and hopefully cure this.
also worth checking - what size raer cassette have you got on? if its a really big tooth count and a short arm rear mech then you might be past the capacity of the mech to cope with the number of teeth on the cassette and be better off with a long arm mech. But check for the chain gap screw first.
hope i've helped

Mister W

The size of the mech is nothing to do with the number of teeth on the cassette. It's to do with how much chain slack it can take up.

The reason the mech is catching only when you're on the small chainring is that the mech is pulled forward when you're on the big chainring. Take a look at the position of the mech when on each chainring and you'll see what I'm saying.

Adjusting the B screw (as above) is the likely cure, assuming you aren't trying to run a cassette beyond the capacity of the mech. Shimano road mechs will go up to 28. Campag can handle 29.

Berk Bonebonce

I doubt the mech comes with a B screw.

And the max rating for the mech is likely to be 26t.

If your largest sprocket is indeed 26 or less, you might want to try adjusting chain length to solve this problem. However, I am guessing that the problem would not exist but for the fact that you have exceeded the max rating for your rear mech.

Campag rear mechs also come in medium cage and long cage/triple.

Mister W

I can't say I've ever come across a rear mech that will only cope with a 26t cog. Campag mechs generally cope with 29t

I apologise, I didn't read that it was a Campag mech so technically it's not a "B Screw" but it does the same thing. Park Tools describe it here - http://www.parktool.com/blog/repair-help/rear-derailler-adjustments-derailleur

dnrc

thanks for the advice chaps,

Its a 27t casette and everything else as far as i could see was right.

I would have just adjusted the b screw except it didn't have one...i thought anyway

This is my first campag bike and it turns out they have had the foresight to move something that was obviously in a place where it was far too easy to see and access!

yakk

Hi there, Mr W, thanks for that link, it's answered a big mystery for me!
I run a campag compact with a 29 at the back (just in case..), and get the derailleur touching the 29 - off to the garage then.
Yak

Berk Bonebonce

Mister W wrote:

I apologise, I didn't read that it was a Campag mech so technically it's not a "B Screw" but it does the same thing. Park Tools describe it here - http://www.parktool.com/blog/repair-help/rear-derailler-adjustments-derailleur

Best link on the entire internet, that. It is not mentioned in the Owner's Manual (at least in mine it doesn't - older Record).