If you had a bad tensioner, that would throw the belt alignment off.
My daughter's 1987 S-10 had one alternator replaced and one tensioner.
Both of the were still working well after 5 years and she sold the
Blazer last year with 218,000 miles on it.  Too bad it had the crappy
2,8 V6 in it.

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Alternator Started Rattling!  

Group: alt.autos.4x4.chevy-trucks Date: Thu, Oct 26, 2006, 9:19pm From:
bobbyswift@webtv.net (bobby swift)
My 88 S-10 Blazer 4.3 serpentine belt lasted a year..then my alternator
starts rattling...it went after about a year and a half...that must have
been what shredded the belt!I replaced the tensioner...it's still pretty
tight..guess things only last a year or so.
          Bobby

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"Sometimes, it is better to remain silent and be thought of as a fool
than to open your mouth and remove all doubt."
~ Unknown ~