Help diagnosing belt driven squeal
 

I have been chasing down a belt driven squeal/metallic grinding sound. I have swapped out belts, and taken belts off to try and figure this out.

The engine runs smooth and quiet until I get the rpm's up to 2800 and then I get what sounds like a metallic grind or squeal.

Has anyone had an alternator bearing issue, but not till you get to about 2800 rpm or higher?

I ask about the alternator because it is the only thing I haven't replaced yet.

Thoughts?

No, or improper (Heavy-duty, Severe-duty) clutch fan? 2800 rpm causes the fan to drag so much the belt slips? 2800 rpm causes the flex-fan to touch the shroud?

HOW do you know that the sound is from something belt-driven, and not a vibration somewhere else?

first i would try spraying belt dressing while revving the engine to see if the sound even changes. then i would put a stethoscope on the alternator.

I just replaced the fan clutch, so I hope that is not the issue. I checked to make sure the fan is not touching the shroud, but I will double check it.

The noise is dependent on engine RPM, usually right around 2800 or higher.

I will try the stethoscope method

Are you 100% sure the sound is coming from the front of the motor?
If the car has a auto trans I have heard a cracked flexplate sound all too much like belt slippage.

2 widths for belts. Make sure you have the correct width for the pulleys you're driving.

Run the car down the road with the alternator belt off. That should rule it out.

I have the exact same problem — squeal starting around 3k rpm, and I too just replaced the fan clutch. I swapped out the standard duty for a heavy duty and did the mod to the bimetallic strip to start it sooner.

I roughed up the pulley grooves a smidge and I’m going to try slightly wider belts.

Forgot how much fun it is shopping for v belts . . .

So you've dramatically increased the load on the belt, beyond what the fan system was engineered for, and you're wondering why it slips?

Just about everyone on the forum runs the Hayden heavy duty clutch, and many run the severe duty. The heavy duty is also the only version Hayden’s application guide lists for my year 455.

In any event, I don’t remember saying anything about wondering why it slips . . .

The new belts fixed my squeal. The issue wasn’t the new clutch exceeding the OEM design, but the current slate of available v belts on the mark. Many of the belts that are listed as correct are actually sized metric, which ends up a bit narrower than the stock 7/16” width. Gates, which makes a good belt in general, says their 7000 series belts fit and lists them as 7/16” width. But they are actually 10mm, a bit narrower than 7/16.” Goodyear Belts came out with a new line of belts, and the width is almost exactly 7/16,” just a hair over. That’s what I’m trying now, and they seem good quality so far.

Got a name for the new Goodyear belt line? Wouldn't mind filling that away for future reference.

The line is imaginatively named “Goodyear Belts.” At the moment the best place to get them is Amazon.

https://goodyearbelts.com/

Thank you. Checked their site and they list a good selection for Pontiacs. And yep, just a few hundreds over 7/16.