Quote Originally Posted by DebW View Post
The small cog is susceptible to too little cable slack but not to too much cable slack, assuming the limit screw is set correctly. You should also consider cassette wear. The 12-tooth cog will wear noticably faster than the other cogs, because it is smaller and goes around faster. If you've got more than 1000 miles on this cassette, there is potential for this kind of wear.
Brand new cassette and chain. Maybe 75 miles on them, and I doubt that any of those miles used the 12. I'm getting a little befuddled by this problem, and am beginning to wonder if I have a faulty 12-tooth cog?