Cervelo S3 sounds like a bag of spanners

[oldgreyandslow]

Hi, I'm looking for a bit of help. I changed the rear mech on my S3 for a long cage version and changed the cassette to a 34-11, it's an age thing.
Anyhow since the change it sounds awful, it seems to be clattering at the rear and I can't seem to work out why or where it is actually coming from.
I thought it may be wheel related so changed the cassette to another set of wheels and no change. It doesn't make as much noise when freewheeling and definitely makes much more when riding over rougher surfaces, so that's pretty much all the roads round here. I may have to change back to my 28 cassette to see if it still does it but I can't think that changing to a long cage rear and upping the cassette should have made such a difference, I fitted a new chain and made sure the length was correct as per the Shimano instructions too.
Any suggestions much appreciated, thanks.

 

[DCLane]

Could be simple things; is the chain threaded through the rear mech correctly? Is the quick link catching? Is the rear mech correctly aligned/adjusted? Is the chain catching on the front mech as it's running higher from a larger cassette?

On an S3 it should be smooth whereas this sounds like it's linked to the rear mech.

 

[dodgy]

As DCLane says, I'd check the chain routing through the rear mech, it's amazing how often this happens if you're not careful.

 

[Illaveago]

Your description sounds a bit odd ! I originally thought that the idlers may be coming into contact with the rear sprockets but you say that the noise is still there but less when freewheeling.
Does the noise change when you select different gears ?
A constant noise whether pedaling or freewheeling seems to rule drive train related issues.
Something coming into contact between sprockets and spokes should disappear when pedaling .
If the noise alters in frequency depending on which gear you are in would suggest drive train . If it alters due to the speed you are going then it would suggest wheel or bearing issues .

 

[si_c]

Two things likely to be the issue - chain routed through derailleur incorrectly or the b-tension screw needs winding in.

 

[ColinJ]

Two things likely to be the issue - chain routed through derailleur incorrectly or the b-tension screw needs winding in.

I put a new chain on my best bike before rushing off to meet someone. The chain was really noisy on the ride over to the meeting place. It was only when I got there that I realised that I hadn't got it routed inside the derailleur properly!

I had b-screw problems when I fitted a larger cassette to a bike. The screw wasn't quite long enough to completely stop the rumbling sound in the biggest 2 sprockets. I did a temporary bodge by making a shim from the side of an empty Coke can. I intended to replace the screw with a longer one but the shim has stayed in place and has worked fine for over 5 years so I never bothered to do that.

 

[si_c]

I had b-screw problems when I fitted a larger cassette to a bike. The screw wasn't quite long enough to completely stop the rumbling sound in the biggest 2 sprockets. I did a temporary bodge by making a shim from the side of an empty Coke can. I intended to replace the screw with a longer one but the shim has stayed in place and has worked fine for over 5 years so I never bothered to do that.

You can take it out and feed it in from the reverse side to solve that problem too.

 

[Cycleops]

If you’ve threaded it correctly you could try adjusting the B screw but it may be that your existing mech won’t handle the 34t sprocket. What make and model is it? Hold the back wheel up and look closely, is the top jockey wheel running too near the cassette causing the noise?

Edit: Check reveals you have a Ultegra R8000, if it's the short cage max capacity is 30t so 34 might be a bridge too far.

 

[fossyant]

Check the B screw ! Top jockey might be too close to the cassette.

 

[Ming the Merciless]

Time for a new bike

 

[oldgreyandslow]

Thanks folks, will try to fathom it out this evening, just to clarify I changed to a long cage rear mech specifically so I could go to a 34 rear with the semi compact front so I am pretty sure that's OK, bloody better be as it's cost a few quid on the new bits.

 

[oldgreyandslow]

Still not sorted, I reckon 34 rear cog may be too much with a 36 front, despite, I think, being within the spec of a long cage rear mech, I'm going to put the 28 back on the rebrand see if the spanners disappear. It's a right PITA

 

[si_c]

Couple of pix might help get a diagnosis

 

[oldgreyandslow]

The reason is blindingly obvious now and an epic fail on my behalf.

The bike is fitted with 6800 Ultegra, I changed the rear to a GS which can take up to a 32 tooth rear sprocket. I confused this with my other bike which has an 8000 series which can take up to 34.

So now I either fit a new rear cassette with 32 or buy the 8000 series rear mech' if it is compatible with 6800 shifters!

 

[JuhaL]

When you change the cassette to different ratio and rear derailleur you might need to check length of a chain and maybe you need to adjust b-tension screw as well to adjust pulley wheels better distance from sprockets.