The HG-70-AC (11-28T) should work, so long as your derailleur cage is long enough. I'm guessing you might have short cage rear derailleur since the cassette you're looking to change out is a very narrow range HG-70-7J (13-21T). Pretty much any 7 speed Shimano cassette is interchangeable, it's just the teeth range and derailleur wrap you need you to worry about, which also takes into account range of teeth up front on your crank. What type of bike and what derailleurs/shifters/crank do you have now? The HG-70-AC (11-28T) was a very popular MTB cassette around '94-'95, just before the switch over to 8 speed. The HG-70-I-AN was the 8 speed equivalent and started up around '96. The Shimano LX derailleur from these years was a very popular (and durable!) spec for these cassettes.
<EDIT> after checking your other links I see you just want to trade out a single cog on your existing cassette, to up your high gear? I'm not 100% sure of the compatibility of just changing out the small cog. If it does work, I don't think you'll like that big jump shift from 11 to 14 teeth.
According to Sheldon
"There is no problem mixing 8-speed sprockets into 7- speed cassette."
Last edited by RaleighComp; 10-28-10 at 01:30 PM.
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