Splendidtutiona

I have been having this problem basically since I put my '73 Raleigh Competition back together. I used a full Huret Challenger group to save the Jubilee stuff, since I had intended this to be a go everywhere bike and set it up with 32c 'cross tires. Anyway...
when Im in the small chainring, about midway through the cassette, maybe the 20t or the 24t cog, I get a very audible 'clunk' with about every pedal stroke. I have adjusted the bottom bracket tighter, looser, tighter again, no changes. And it only occurs when I am in the aforementioned gear combos. i have tightened the rear derailleur into the frame, tightened the "locknut" on the back of the mounting bolt, I ahve tried various positions of the cage/pulley screw thar ounts the pulley cage to the body. Nothing. Same noise, and only in those gear combinations, and only while pedaling under load. It gets louder with load.

The 'only' thing I can think if is this. There is a very thin washer between the pulley cage and the body. I have seen some diagrams of later versions of this derailleur (thanks disraili gears!) that appear to have a similar washer between the screw head and the pulley cage, but I cant see it on earlier versions.

I am a little at wits end. The chain is new, the freewheel is new, I'm pretty sure the links aren't sticky in the chain.

Anything that might be the cause of this? It seem like I can 'hear' and 'feel' the clunk through the shifter and cable, but since both of those are attached to the frame, it is probably just transmitting through there. Great bike. Good drivetrain, just cant get this little clunk worked out. Oh, T.A. 3 pin professional cranks, original to the bike.
Anything?

cheesesandwich

Probably the new chain needs break-in. Just changed new chain and happened to me on 1 certain gear especially under heavier load, like starting from stationary position. I tried using easier gear first before moving to that. Slowly after a few rides it will get better. My last ride I don't remember it making that sound.

stevel610 

Perhaps a bent derailleur or derailleur hanger.

ClydeClydeson

Very possibly a stiff link in the chain. Sometimes a stiff link is pre-bent in such a way that it rides through some gears fine and only acts up on certain other gears.

ANyhoo, your description of a 'clunk' that seems to be timed related to crank revolution is the classic symptom of a stiff chain link. It might be damaged from a rough shift or some other misadventure, or you might have created a tight link when connecting the two chain ends. Many chain tools have two sets of holders for the chain - one directly against the back of the tool so the back plate is held so the pin can be pressed through, and another set where there is nothing supporting the back plate so pressing th epin spreads the plate ever so slightly, and will free up a link made stiff during installation,

ClydeClydeson

OH! Also,
another remedy for a stiff link is to grab the chain on either side of the stiff link and try to bend it sideways at the stiff link, back and forth. THis spreads the links a bit like the chain tool.

To find the stiff link, turn the cranks backwards and observe the rear derailleur - when a stiff link passes through the derailleur, it will jump a bit.

Bianchi84

You say "every pedal stroke" so I'm thinking NOT chain since a bad link would probably not be interacting with something on every stroke. My guess is BB ... bearings, cups... (Maybe crank arms?). Maybe that preferred gear combo is getting your greatest effort and that's why you're hearing and feeling it. Drop the chain off of the rings, grab the arms and really check for play. Rotate a little and repeat. You may have tightened the bearings but if they're unevenly worn or something, things go out of adjustment. Clunk always says BB or FW to me if it really is at every pedal stroke.

Duke7777

I would say this is due to excess play in your freewheel. When you are on the middle cogs, the freewheel rocks back and forth with each revolution of the wheel. You could try a different freewheel to see if the clunk goes away. The solution is to remove the freewheel lock ring and remove/replace shims as needed.

MB33 

Sounds like the freewheel. I have a couple bikes with freewheels that clunk on about the middle cogs. One of them is a brand new 7speed Shimano with a brand new chain and NOS crankset and derailleurs. It clunked ever since day 1. It's weird because on both of them it seems to come and go, or it requires the chain be at a very precise point in order to clunk.

Drillium Dude 

Check the cog(s) for damage, too. While this does sound a lot like a stiff chain link issue, if you hear it ever pedal revolution there would have to be more than one stiff link, while the cog goes around much more often. The noise you describe is exactly what my drivetrain sounded like when I split a cog a couple summers ago.

DD

plonz 

Like the other respondents, I’ve had very similar clunks occur with sticky chains, freewheels with too much end play and old bearings in bottom brackets. Sounds like you’ve eliminated all those as potential causes. Might look at the chainline although I think that would cause more problems at the high and low ranges.

I would watch it on a stand and look very closely for sudden chain movement anywhere in the drivetrain. Even if you see this, it can still be difficult to pinpoint the cause. I remember the first sloppy freewheel clunk I had being a real PITA to diagnose.