1994 B350 - still having issues with getting the belt to stop squealing. I've had several mechanics troubleshoot it, and have swapped numerous parts. I suspect that something in the configuration of pulley sizes is slightly off.

Hoping maybe someone who has this same van could tell me what parts they have used for the idler and tensioner pulleys and belt?

 

Serpentine belt, right? Squealing is either dirt in the pulley grooves, worn out belt, weak tensioner, or bad bearing on something it's running.

 

Belt tensioners usually have an indicator on them, when lined up means the belt is stretched and it is time to replace it. If they don't have an indicator, I remove the belt and draw a line straight across the two moving parts. Reinstall the belt and take a look to see how close those two lines now are. What I have been finding, is that even with a new belt, the tensioner indicator is almost all the way over and the two lines are very close to each other; it is like the belts are 1/2" too long from the get-go. I have had very little luck with Dayco or Gatorback belts, and have had the most luck with Bando belts.