Expert: Skip Bollinger - 10/9/2007

Question
i have replaced all the belts on the truck however i can unable to stop the belt that goes from the crank to the alternator from resonating...the belt feels tight when the truck is off however when it idles it vibrates. The more i pull on it the more tension on the pulley i put which is not good for the alternator's baring could i maybe get some ideas on what can do to prevent the vibrating?

Answer
Travis,
  Is it making noise? A belt is rubber and on "long runs" such as between the crankshaft and alternator, it will flex. When you rev the engine off idle, does it tighten up and, again, does it make noise? Are you having trouble with the engine "eating" belts? Are you having trouble with the engine throwing belts? If you aren't having trouble with noise or using up the belts, it could be, as Shakespeare said, "Much Ado About Nothing".
  If you are having trouble with name brand belts such as Dayco, Gates or Goodyear, you might try to get a Motocraft belt. The number should be JC577 if the truck was made after 11-88. You might also check with Ford to see if they have retro fit kit that puts an idler pulley on the belt between the crank and alternator. There is nothing in the aftermarket for that.
  Travis, that is about all the damage I can offer. I hope it helps a bit. Please remember I'm a Parts Professional, not a Tech but these thoughts are the best I can do. I hope they helped or at least give you a bit of direction. Thank you for your question..
Skip