1993 F350 Serp Belt comes off when down shifing on 1993 Ford F-350

1993 Ford F350 Non Turbo 7.3l 4x4 crew cab dually 4 speed trans. My sepentine belt comes off when down shifting, why? whenever i down shift my truck from any speed, the belt comes off the pullys and shreds up, I replaced all idler pullys and all acceceries pullys and made sure everything was aligned up and they are, I replaced the belt 6 times and still does it. any suggestions?

by in Joliet, IL on September 23, 2010
2 answers
ANSWER by on September 23, 2010
Did you replace the tensioner as well? And look at your Crankshaft pulley, and see if the balancer is worn out. You can check this by looking at your Crank Pulley while it idles, if it wobbles, then that could be the culprit.
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ANSWER by on September 27, 2010
Number one thing i would check the harmonic balancer or the crank shaft pulley try that make sure that this is not your problem and the tensioner should always be motorcraft.
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