Countdown48

I'm trying to tune up my cannonade f400 to sell but am having trouble on the smallest cog. It skips almost like it slipped on a tooth and then catches again. It only happens in the 11t cog and happens in every chainring. Otherwise, it shifts perfectly. I tried replacing the rear derailleur, the 11t cog, the chain, the free hub, and even tried changing the chain line but nothing has helped. The 11t cog I replaced it with isn't new but only one tooth shows signs of wear and is a little rounded. I am all out of ideas. Is there something I am missing? thanks in advance for any suggestions or help!

Here are the components if that makes a difference:
7speed rear, 3 front
Shimano STX rear derailleur, alivio front, gripshift shifters

Shinkers

Lockring is too big?

fietsbob

cog worn, chain worn, replace cassette & chain?

ThermionicScott 

That would be my guess. If the cassette originally used a 12T+ first cog, and it was replaced with an 11T, the lockring from the original cassette will be too big and allow the chain to ride up and skip over the cog teeth.

prathmann

So you have a couple worn-out 11t cogs and are wondering why they both skip. It's very common for the cogs with the fewest teeth to wear out quickly since the stress is concentrated on fewer teeth. Using a new chain just makes things worse since the spacing doesn't match the worn out (rounded) teeth on the old cogs. Get either a new 11t cog or a whole new cassette. The latter would also ensure that you get the right size lock ring.

elmore leonard

Any good bike shop should be able to help you fix it. I would think? I'm guessing the chain is trying to move off the small cog and the shift cable needs adjusted, the high stop or the cable hangar is bent.

Spoonrobot 

That's it.

That's the problem right there. Small cogs wear very fast.

79pmooney

Yeah, you have two possible problems; the second cog being worn and the lockring. Did this wheel come with a 12 tooth sprocket and you went to 11? (I had the same issues on my fix gear when I swapped to the 13 tooth cog to ride 1600 feet of descent. I thought I was cool since the cog was 13 teeth, not 12. I had the special lockring for the 12 sitting at home.)

See if the chain hits the lockring or is very close when you are on the 11. (Maybe easiest seen with the wheel off the bike and an old chain.) Get an 11 tooth lockring if it is close.

Ben

2manybikes

Did you already adjust the limit travel stops for the derailleur? It can keep the chain from going all the way to the end of the cassette. Same for the high end adjustment. When switching a cassette it is sometimes needed.
You should check it every time you switch cogs or the lock ring. Since it is not needed most of the time, many say you don't need to adjust it. Not true.

Retro Grouch 

How's your "B" screw adjustment? Try backing it out until the jockey pulley just misses when the chain is on the largest rear cog. That'll give you more wrap when you're in the smallest cog.

Narhay

I'd get a new cassette. They are dirt cheap and you can change your gearing at the same time.