boomwater

Have had a problem with the derailleur. Intermittent clunk and chain skip when riding. I had a problem with chain suck about four months ago and the rear derailleur jockey cage got bent so had to get a new one. This stopped the "suck" but ever since I have a intermittent clunk from the gears when riding on large and small front rings and in pretty much all the rear cassette gears. The chain skips and gives a almighty clang and then is fine for a bit then does it again. I have a brand new chain and the cassette has only about 700k on it. I know...should get new cassette with chain but didn't think the cassette was at all worn out and anyway it was happening on the old chain too.! Everything is ultegra and the chainset has about 1000k on it. I had the rear hanger checked for alignment and was fine. (colnago c40 frame). I am just running out of ideas on what could be causing this! Oh, The front big ring does show a bit of wear but nothing nasty and it happens in the big and little anyway so didn't think it was this. I suppose next thing is new cassette? or?

m

cny-bikeman

The symptoms sound somewhat like a tight or damaged chain link, which does not always occur, and when it does occur is less often than every pedal revolution. As the chain has over 100 links it will occur a bit under at most once every 2 rev's of the large chainwheel and once every 3-4 rev's of the small one. Although the chain is new it could be that it was not installed correctly. The biggest difference between skipping from a link problem and one from wear is that a bad link will skip more under low pedal pressure.

The best way to spot it is to shift the chain onto the small chainwheel and one of the smaller cogs (not so small that the chain rubs on a larger chainwheel. Turn the pedals slowly backward and look for the pulley assembly to "jump" as the tight link goes through. You can also push the derailleur body slightly forward to reduce tension on the chain further, which enables you to see more subtle problems.

boomwater

Hi CB,

Yep, I tawt that too but it's definately not that. No problem with chain and it was doing it on old chain too. And its's not a regularly timed problem either! I can be pedaling and hear a slight click then go another k or 2and suddenly it will clang and catch and then nothing for a little while again. Could it be frame flex?

cny-bikeman

As you said "ever since..." I was under the impression that the chain was replaced then, and I missed the comment about it happening on the old chain. Given the new info, the only thing that would be consistent across all gears and produce the symptoms you describe is the freehub. This is simple logic - The pulleys would not affect skipping, as the chain is not under tension there. A cassette cluster will never skip on all gears with a new chain, and chainwheels would show a problem only under extreme wear or where one tooth has a problem, which would occur every rev. The chain is not it as the problem continued with a new chain. The only component left that is parr of driving the bike forward is the freehub mechanism. I would suggest you replace it.

p.s. "tawt"?? Is that like Tweety's "I tawt I taw a puddy tat" (before many folks' time)?

miamijim

'Chain Suck' is caused when the chain fails to dis-engage from the chainrings while pedaling forward. Is there a chance your front rings have so much dirt on them the chain fails to properly dis-engage? Distorted chainring teeth cause chan suck as well, a distorted tooth catches on the chain thus preventing proper release.

I doubt it's chain suck in the true sense of what chain suck is, its exceptional rare to see it on both chain rings.

I think its a stiff link. Stiff links dont always hang up with every revolution of the chain, they can be very intermittant depending on different variable like pedal pressure.

cny-bikeman

It would appear that the OP knows about chain suck and said he is no longer having that, and as you point out it's extremely rare on both chainwheels. As the problem occurred with two chains it is not a tight link, which I addressed earlier. There is no reason to suspect them over a freehub problem.

miamijim

Altough you addressed it it doesnt mean its not happening.

cny-bikeman

What I mean is that I addressed how often a tight link occurs and how to diagnose it. The primary reason to pretty much eliminate that as a factor is that the problem remained across two chains, as I also noted. The symptoms match what would happen with a freehub whose pawls are no longer operating properly, and the freehub is one part of the drivetrain that has not been replaced. Actually, the OP could try flushing it out before resorting to replacement.

boomwater

Sorry not to get back right way been away . Bikeman spot on I think. I swopped my backwheel and no problems! The old wheel was a dura ace 9speed hub which I believe should work fine with 10 speed (but didn't!) Have a ultegra 10speed hub now with the 10 speed cassette.

Thankyou everyone for info/comments and shall now go and see if I can isolate that squeak! Blimey! Always something.

m

boomwater

Oh, and yep, it must be something in the dark reccesses of my brain but "Tawt' is from the cartoon which ...er hum!...I watch a lot. Now and back in the last century!