So, yesterday I picked up a second-hand Tifosi CK7. It came with a Shimano 105 5600 groupset in the triple chainset configuaration and a with medium cage derailleur.

THE PROBLEM IS that when the chain is shifted into the middle or small chainrings, the upper pulley wheel of the derailleur rubs against the cassette, making a fairly loud rambling noise when turning.

Of course, my immediate thought was to adjust the b-screw, but this is already maxed out. One observation I made is that while in the small chainring, the chain tension is really low, causing the chain to sag notably. I’m not sure whether shortening the chain alone will resolve the issue though.

Any advise?

Thanks,

Pete

Is the B-tension screw pushing against anything? I have seen hangers where the part that the screw is meant to push against has worn and the screw slides past it.

I have seen hangers where the part that the screw is meant to push against has worn and the screw slides past it.

I had that exact problem, although a new mech fixed it – was a combination of a worn mech hanger and ‘slop’ in the b-axle assembly.

Shorten your chain so you know what you’re working with, and check that as Mister P says. And no need to randomly embolden bits, I think most people can decide the salient points themselves!

Oh, but I had so much fun with the emboldening!

Anyhow, thanks for the advice. Yes, the b-screw does indeed have something firm to push against. I think I will shorten the chain first, then see if it’s the derailleur.

You can fit a longer b-screw, but you shouldn’t have to unless you’ve got a massive cassette on there?

how big is the cassette? – and is the mech compatible with that?

I would need to double-check, but I’m pretty sure it’s an 11-25.

Something not right for sure. Is your cage springing back properly, or is it sticking? That could cause both problems.

Push the cage forward by hand, it should have good spring tension.

Speciaized fit different length hangers on the same bike with different specs. Here is a pic of two hangers off Roubaix bikes; the shorter one came on a Comp bike with 11-27 Ultegra and a short-cage derailleur, the longer on a Sport version with 11-30 105 and a medium-cage derailleur. This might explain the problem with your bike if the previous owner has been swopping parts around.

Shouldn’t do with an 11-25 though.

there is a small chance that it has the wrong size jockey wheels in.

They should be 11T i think.

I had the same issue with my Tarmac when I stuck an 11-30 on it despite the mech being good for 32 according to spec. Turned out I had the shorter mech hanger shown above so put a slightly longer B screw in (it literally only need about 1mm more).

Swapping back to an 11-27 made the issue go away so, as njee says, it shouldn’t happen with a 25.

there is a small chance that it has the wrong size jockey wheels in.

They should be 11T i think.

You’re not gonna get bigger ones though, and smaller ones won’t cause rubbing.

Take off the rear mech and bolt it back on with it behind the stop on the hanger. At least that is what I screwed up on my rear mech once…

You’re not gonna get bigger ones though

Dura Ace 7700 GS has 13T jockey wheels.

Still available here

Resolved (well, almost) – I removed about 3 or 4 chain links and the problem went away, except for when I’m in the small chainring and in one of the smaller cassette sprockets (shouldn’t ride in such a combo anyway).

I might still try a longer b-screw at some point. Anyone know where I can get one from?

Take off the rear mech and bolt it back on with it behind the stop on the hanger

This ^^^^

I fitted a Rear Mech’ incorrectly and had exactly the issue you describe. I took it off and checked/re-fitted it and the rubbing stopped.