Hi Folks,

I have a problem with the second gear on my freewheel when both chainrings are used. It seems that all the gears will run smoothly 1-7 except when the second cog is engaged, then I get a kind-of clunking sound as though the chain is catching on something. I've checked the alignment which seems as good as it can be and as far as I can tell the frame is straight. Also it doesn't seem to be catching on the arm of the derailleur or rubbing on the front derailleur.

The components are new: new 7-speed chain, chainrings on the front and freewheel on the back. All new cables and the shifter is the old downtube friction shifter which, obviously, I can adjust incrementally to make sure all the gears run smooth. My rear dearailleur is an NOS Campagnolo Victory and seems to move fluidly and with no problems.

My hunch is this is just the crossover of the chain, but I'm a bit perplexed as to why it is just the second cog on the freewheel that seems to jitter and with both chainrings. On previous bikes I've never had this with both chainrings only the large one.

Any thoughts would be very weolcome.

Thnak you.

Gerald

Might help to know what you mean by 2nd cog - is it 2nd smallest or 2nd largest. Crossover of chain is not logical, and one chainring would have pretty good chainline, and the small cog would have worse chainline in any case. Also not rubbing of pulley cage, as it rotates significantly when on the different chainrings. Chain is obviously a constant. I don't see it being the derailleur or hanger being twisted, because that would be very unlikely to affect only one cog but in both chainrings.

That leaves the cog itself or something odd in the freehub mechanism that only reacts at that particular distance of the chaiin from the center (this one is only theoretical, very unlikely). Inspect the cog to see if there are any burrs or other imperfections that might cause a problem.

If you don't find anything we need to know the frequency of the "clunking," and whether or not you can feel it significantly or it's just a sound. Put the drive train on the small chainwheel and count how many "clunks" in one revolution. If it's something on the cog the number should equal the teeth on the small chainwheel divided by the number on the cog. If it somehow is nto we need to know what the count is.

The cog could also be cracked.

Sorry I've not got back sooner. By second cog I mean second lowest (2nd largest) on the freewheel. I've had a good look and can't see any burrs or defects on the cog. I've turned the wheel painfully slowly and the chain seems to fit fine, the clunking still happens. There is no rhythm to it. Sometimes it'll clunk 2-3 times, cometimes once only. It sounds like when you're free-wheeling and then engage the pedals; as the freewheel picks up the slack there's that kind-of clunk. But in this gear there is no slack. I run the rotation smoothly with tension and there is still a kind-of hollow clunk. I've checked the axle and spokes in case its coming from somewhere else but resonating through the freewheel; but axle is tight, spokes are fine. I'm beginning to think it must be the freewheel iteslf and will probably take it in to have my old one (no problems with that) put back on just to see.

Many thanks for your ideas

Gerald

Check that your derailleur is low enough that there's daylight - 1-2 links of chain free between the upper pulley and sprocket. Often a misadjusted B screw will have the pulley touching the cassette through the chain, causing the RD to get kicked back because of interaction between the two.

Also double check for any stiff links, by backpedaling slowly while pushing the lower pulley forward to slacken the lower loop.

Lastly, it could be a cassette spacing, RD trim issue. Sometimes the spacing isn't dead on, and with the jockey wheel so close there's no room for the chain to flex enough, and it'll ride up on the edges of the teeth. This is most common on new cassettes, as later the chain rounds off the tops of the teeth making engagement smoother.

Many thanks for that. I'll have a good look tomorrow.

seeing as how it's only happening on one cog, i'd try to swap out the freewheel or cassette to another bike or swap in one that is known to be serviceable and see where that goes. of course you don't want this to COST anything, so borrow or rent.

Hi I think that's probably what I'll do. The rear dérailleur is a NOS campagnolo triomphe so there's no b screw to adjust. I've had a good look and there is 1-11/2 links between the top jockey and the freewheel so it doesn't look as though that is the problem - the jockey wheel clearly has distance from the freewheel. Local bike shop thinks its just a case of needing time to bed in. I'll give it a few more miles, if it hasn't sorted itself by then I think I'll change it for the old one which was never a problem. Many thanks for all the suggestions.

You keep saying "freewheel". Is it really a freewheel? I have an old Sun Tour ultra six freewheel and sometimes, but not always, when I'm in the 3rd smallest cog it will clunk-clunk-clunk continuously as I pedal. If I just backpedal a little and then start forward again it usually goes away. Doesn't do it in any other cog and doesn't do it every time. I think it has something to do with the bearings being slightly out of adjustment, but I'm not sure about that and so far haven't felt like trying to adjust it. Hope this can be of some help.

Given what you have checked and what you describe I only have one idea remaining, and it's one I had earlier but felt it was not a good idea to throw out such a longshot before other items were addressed. I'm thinking there is some sort of defect - casting, missing spacer, etc. in the rotating mechanism, and that the leverage and angle on the 2nd cog is just right to cause the body to shift. That could cause a clunk similar to engagement and would likely be irregular.

i had a similar problem with a single speed shimano freewheel. i finally decided the freewheel body was "rocking" on the pawls. probably because something wasn't as square as it should be. coasting, then re-engaging on a different set of serrated teeth inside the freewheel, similar to yours, would fix the problem until i re-engaged those same teeth some time later. i eventually bought a new freewheel.

Hi Many thanks for that. I'll take all the advice I can get to sort the problem out so for sure I'll try the back-peddling tomorrow. And yep, definitley a freewheel. It's kind-of a retro build using NOS on a Reynolds 653 frame. Many thanks.

Thank you. I think you're right. I've tried to think of all the possibilities but I'm thinking now it has to be a defect somewhere within the freewheel. I do have a freewheel which I've used on another bike, has never given me a problem, so tomorrow I'll swap it over and see.