TurbineBlade

Hey, I just installed a new cassette - a sunrace 7-speed and new 7-speed "Z" chain (kmc) with huge 34t granny cog jump at the bottom of the cassette. I use friction shifters and all the cogs work just fine except the smallest one....which the chain skips over repeatedly.

I have the derailleur high limit dialed in just fine, so I know it's not that the chain is just unable to reach the cog properly. Since I don't ever use an 11t cog on any of my bikes (and only seldom use the 12 or 13), I plan to just dial the high limit to avoid the smallest cog.

What would cause this nonsense? I've gone through 4-5 cassettes on this set-up in the last couple of years and never seen this happen.

Thanks,

DannoXYZ 

How is it slipping? It is rubbing on the next cog over? Is it riding on top of the teeth?

Isolating the cause to either lateral or longitudinal movements can help pinpoint where the problem may be.

TurbineBlade

Sure. It is (was) riding on top of the teeth, not really trying to drop one way or the other.....which is what I thought at first when I was dialing the high-limit...thinking maybe it was trying to jump into the drop out or not getting enough lateral movement to make it onto the smallest cog.

I dialed the little sucker so it won't even drop onto the smallest cog now, but I was just wondering what the deal was with it since the other 6 cogs engage the chain just normal.

bikeman715

You may have your cable to tight. lossen it just a little and the chain should drop in.

TurbineBlade

Nope, definitely not that...I just tried to loosen the barrel adjuster on the rear derailleur to "extremely loose" and it still rides on top of the small cog.

Weird -- setting high limit back to locking-out that sucker .

bikeman715

you sure your hanger is straight ? it could be off just a mm and that can throw everything off.

bikemedic

Is the chain on the middle or big chainring when you are shifting into the 11 tooth cog? If you're in the granny gear the chainline may be too far off for the chain to engage the cog.

DannoXYZ 

Look underneath the cog where the chain moves from the top-pulley to the cog. Is the chain in-line with the cog? Or is it at an angle. Take a picture from directly behind the smallest cog with the chain riding on it for us to see. I suspect it has something to do with the derailleur positioning.

TurbineBlade

Update - problem solved. I'm an idiot.

The lock ring for the cassette was too large (diameter) and was interferring with the smallest cog on this particular cassette. I guess the lock ring I was using came from an older cassette with a 13t cog compared to the smaller 11t this one has.

I had some other lockrings and got it working fine.