Hi,

I get a "clonk" sound when pedalling heavily in a low gear, for instance when going up hill. It only happens when I'm on one of the larger (bottom 5) cogs on the cassette.

It appears to be something to do with the rear mech. I have a new chain, a newish cassette (100 miles or so) and new front cranks. My rear mech is a three year old XT long cage with new (LX) jockey wheels.

So far I've:
-Fiddled like crazy with the indexing. The shifting is fine, but the clonking remains
-Checked the pawls on my rear hub (Hope II). They are all fine and springy.
-Checked for stiff chain links. None.
-Checked the cassette for damage – none. Does not look worn.
-Checked my frame for cracks. None that I can see and it is only a week old anyway.

This is driving me crazy!

Any suggestions?

Thanks,

T

Did you get a new chain with the new cassette?

I bought a brand new chain. The cassette was second hand, but the seller said it only had minor use. He might not have been telling the truth I suppose.

I'm tempted to buy a new cassette and chain now, as this problem is infuriating. It really does not feel nice when your going up something steep trying to keep the front end down when a huge clonk comes from the back end.

Could it be a bent rear mech? I do remember having a few spills with my last bike.

is it just a noise? rather than anything slipping or feeling like it's going to change gear?

I had this once when my crank was too near the chainstay. Under big loads it deflected slightly and knocked the chainstay. I put a longer BB in and it went away.

It feels like the chain is slipping because you can feel the pedals move forwards with less resistance momentarily.

It might be trying to change gear, adjusting the indexing sometimes does help. I've been trying to catch it by looking down, but I've been unable to make it clonk when doing that.

If I stand up in the pedals and mash it goes clonk, clonk, clonk in quick succession. I think the sound is the freehub being banged when load is interrupted and returned.

I should mention that the cables and outers are brand new and where greased when installed.

Have you checked that the cassette is done up tight? Mine made a clonking noise when it worked loose once.

Yup, I made sure it was tight :/

Hmm sounds like a worn cassette – IME they dont look worn when they go – you "just know" as teh chain slips on greatest torque – Not saying it is but i think you been sold a dud – maybe its something else though 😯

That sounds more like the chain slipping round the cassette. New chain/old cassette is a dodgy combo. It might go away as the chain stretches, it might not.

You might get a big bruise on your knee, you might not.

if absolutely everything is tight and nothing has play and you're sure it's not the freehub then it has to be chain and cassette
.
I had this problem on the road bike and it turned out that it was a loose crank and the chain was slipping on the chainring as there was lateral movement

Cool, thanks for the help. I'll give everything a check over tomorrow and if that does not fix it I'll replace the cassette and chain, then the mech.

Not a bad idea to have a spare chain and cassette anyway.

I've just checked the cranks. I can't feel any play when pulling on them.

I have just noticed that my small, small combinations have a rather slack chain. I don't think I can remove anymore links from my chain though as the large large combination is rather tight.

Sounds like your cotterpin is loose.

😉

Does the clonk always occur when your crank is in a paricular position? Eg, the 6 o'clock clonk?

If you've got a HT2 type BB then it might also be worth checking that your plastic top hats haven't broken up, it can give quite a definite knock when pedaling.

Could be your mech. The tension spring looses its, eerrr springiness. New mech

. The cassette was second hand, but the seller said it only had minor use. He might not have been telling the truth I suppose.

perhaps it only had minor use, but with an already worn chain?

It could be the freehub..

I don't think I can remove anymore links from my chain though as the large large combination is rather tight.

Correct.

I have a similar problem on my bike too. My rear mech flaps about on even the slightest of rough ground, i.e. cobbles and makes lots of rattles.

The spring does seem to have lost it's spring. Hoping that I can find a spring instead of changing the whole mech…. it's XTR 🙁

Ordered new chain and cassette. (£70 ouch). Hopefully that will fix it, otherwise the only thing left to replace is the Mech.

If it works, the cassette will go on Ebay – buyer beware!

My mech is rather rattly, perhaps the spring does loose strength after a while.

Bludgeon, perhaps you can find a mech which has been mullered and swap the springs.

You checked whether it's the middle chainring sucking then releasing with the new chain that creates a clunk as the mech springs back 😉

It feels like the chain is slipping because you can feel the pedals move forwards with less resistance momentarily.

Definitely old cassette. New one will fix it.

Chains and cassettes wear together. If you get a new chain very regularly, your cassette will be fine. If you use a cassette for only a few rids with a worn chain, it'll wear the cassette out very quickly. It'll still work fine with the old chain though, but a new one will cause the symptoms you describe.

Basically, new chain means new cassette UNLESS you change the chain very early, just as it starts to wear.

Having a slack chain will not cause a problem with pedalling.

To be fair there are three things I won't buy on eBay – s/hand chains, cassettes and bottom brackets – what I would class as disposable items, use 'em 'til they break then dump 'em.

Easy for a new cassette to do a 'few' miles with a knackered chain to spanner it.

I've got the same problem, which seems to have developed suddenly after I rebuilt the wheel with a brand new Deore hub.

I did ensure the cassette was properly tightened but I'll double check… Maybe loose bearings in the hub?

Have the pawls worn either themselves or the internal drive ratchet inside the freehub body? I had a Ringle hub do that. It made a noise and slipped, but I couldn't work out what was wrong until the day it failed completely. Luckily I was close to home and had just crested the highest point of my ride. The freewheel home was like going chainless 😀

Replaced the cassette and chain and went for a ride. Not a single skip 🙂

The old cassette looked worn when I compared it to the new one.

Yay!

I had a similar issue recently – it was also my cassette at fault.

The chain was slipping and 'sliding' down the cogs on the cassette and off the bottom causing either loss of drive or on one occassion for the rear wheel to lock even though the rear mech was in the correct place – very strange.

A new cassette fitted and the problem seems to have gone and slick shifting has returned.

Good old STW – came to the rescue again 🙂

who stitched you up on the cassette then, was it from classifieds?

Cassette:£15 (9spd shimano HG61 11-34, light use)

I think the culprit is in the classifieds – prob took it off thinking it look OK and rode OK with an old chain but prob far from new 😉