serpentine belt question

[Guest]

ok, so riddle me this -

when replacing a worn out belt with a new one, the new belt pops off almost immediately after starting the engine, where as the old belt runs just fine.

i double checked and the new belt is the appropriate size, although it is a little different than the old belt. i'm guessing that's because the old belt has stretched.

[v8nightmare]

if the belt is indeed correct, im thinking whether its a standard or an Auto tentioner the causes could be-
worn tensioner
worn pulley[s]
tensioner not, tightening, or being tightened all the way
installer error
dark magic
or the type of belt you have just doesn't fucking agree with your pulleys for some odd reason

[Guest]

well, the harmonic balancer does not seem to be wobbling.

The power steering pump does not cause the belt to squeal under the usual tests

the alternator and AC both seem to spin fine.

I did replace the idler pulley and the tensioner. the idler pulley had shot bearings, and the tensioner locator peg had broken off. still same results.

[BIGEVIL]

With out seeing her, the common denominator is the tensioner and idler pulleys that you replaced. Could one of them not be square and true? Even the slightest deviation will kick a belt off.

[Guest]

turns out there was a broken bolt in the power steering pump bracket as well as a support i neglected to put back on after the head gasket job last year.