SigForum Brain Trust,

I'm having a hard time diagnosing this squeal coming from the front of my 2000 Bravada with the 4.3. It is soon to be my stepson's truck, and we've been working on it for when he turns 16.

At first, seems like it was the standard tensioner & pulley noise that frequents my GTO, so we replaced the tensioner, idler pulley, and belt.

It seemed to help, but the noise didn't go away. Found a hint of play in the alternator pulley, so found a deal on a NOS AC Delco Alternator and swapped it out today. Noise got worse!

It sounds like it is coming from the valley, but I'm having a hard time pinpointing it. I've done the screwdriver to ear thing, and nothing stands out.

I've ran the truck with no belt, and the noise is completely absent. AC compressor on or off, doesn't make a difference.

I'm thinking either:

1) Bad "new" parts, get a new tensioner, idler pulley, and belt.

or

2) Water pump bearing is on its way out, and a new alternator removed some play from the system, with made the noise worse. No leaking from the weep hole though, and every time I've had a GM water pump go out, it leaks first.

Sorry about the video, but not sure the best way to describe the squeal.

I know there's a wealth of knowledge on Sigforum, hoping someone has a good idea, before I continue to throw more parts towards it.

Thanks!

https://youtu.be/g6NN3xZxtus

Have you shot (spritzed) some soapy water on it to see if you can make it go away?

quote:

Originally posted by Krazeehorse:
Have you shot (spritzed) some soapy water on it to see if you can make it go away?

I have, doesn’t make a difference on noise.

Diagnosing belt noise (Note: this is a good site with a great deal of info, but it has some annoying pop-up ads that, ironically, are for an ad blocker service.)

If spraying water (never dressing or WD-40!) on the belt doesn't change the noise, and the noise is absent with the belt off, it doesn't sound like the belt itself, it pretty much has to be a pulley. The alternator, tensioner roller, compressor clutch hub bearing, the water pump, or (if equipped) an auxiliary air pump or idler (on the left side as you face the car, between the alternator and crank) are all possibilities. (I know you replaced some of these, but sometimes NEW stands for Never Ever Worked.) With the belt off, spin all these pulleys by hand and see if any squeak. For the water pump, grasp the ends of the fan blades and try to wiggle the pulley. A tiny, minimal amount of play is normal, but visibly rocking back and forth is no good.

For what it'sworth I agree with egreore. Removing the belt eliminated most of what could have caused the problem.You may be able to feel a grinding just by turning each pulley by hand.

Jim

Look closely at the water pump pulley to see if there are any cracks, especially near the bolts.

I had a 99 Tahoe that had a serpentine belt that would squeel anytime it was cold out. Well after exhaustive diagnosis, multiple new belts and a new tensioner and finding nothing wrong with the drive accessories, I turned to this forum for help.

One person said to get a Goodyear Gatorback belt as it has a slightly different design with its crosshatching on the one side. I did and the squeel went away. I recommended the same a friend a few years later and his squeel went away too.