I just replaced all my belts and the a/c alternator belt squeals at turn on. Just how much deflection should the belt have? It did the same thing before especially when the a/c is turned on. After warmup the squeal goes away.

 

1/4 inch deflection at the most. try to get it slightly less.

 

yeah I agree1/4 inch deflection MAXas you push on the longest span, we're talking banjo string tight for that belt.

 

did you get any grease on the belt? if so use some belt dressing to clean it up

 

Thanks for all the help guys! The tension was way toolow causing the belt to slip. I just followed the original belt tension as a guide but it was apparently way too low. At a 1/4" the tension is pretty firm, but no more squealing.

 

the squeal noise is caused by friction between the pulley and the belt, most people can understand that grease and oil are commonly used to reduce friction.