Belt keeps sheding and coming off. both pulleys have been replaced
There is no adjustment on the tensioner, it is automatic. Either the complete tensioner is loose and needs to be replaced or one of the accessories is locked down and causing it to slip and tear. Take the belt off and see if you can spin the alternator, power steering pump, water pump, and a/c pulleys by hand. You should be able to spin everything except for the crankshaft pulley. It is fairly easy to replace the tensioner assembly, it is held in place by only one bolt.
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