Help! Horrible noises when belt is on, but all bearings seem fine without belt

I broke the serpentine a couple weeks ago when "misbehavin". I've gone through the entire serpentine system, checked all bearings, replaced idlers that seemed worn, replaced tensioner. It ate a couple more belts (stripped off a rib), and then started squeaking, and now making really scary crunching, cracking noises. Something is coming apart, I can see the tensioner jumping in time with the horrible noise.

Runs smooth and quiet without the belt, all the idlers spin nice and firm, as do the alternator, water pump, AC and power steering pump. I'm stumped.

Is this what an AC compressor sounds like when it fails? Or maybe just the clutch? If so, why does it spin smooth without the belt?

Any ideas on how to diagnose / fix? I truly appreciate everyone's experience and help!

Have you checked the alignment of the pulleys and idlers?

there were a few threads years back with issues that caused belt issues and it was alignment issue s

stkjock said:

Have you checked the alignment of the pulleys and idlers?

there were a few threads years back with issues that caused belt issues and it was alignment issue s

Click to expand...

What he said.
Have you also checked the harmonic balancer? It's possible the rubber sandwich has perished causing the outer ring of the balancer to separate.

Both are correct. Description sounds like a misalignment and the first place to look is at the harmonic balancer. That separates and causes what you have experienced.

Most important. DO NOT CONTINUE TO DRIVE IT!

Thanks guys! I never would have thought of that but I agree that's probably what it is. I haven't had time to get back into it yet, but I'll respond with results. This would actually be a relief, I was envisioning a big buck repair.

and no I won't drive it, thanks

I took it to a shop (drove it there without the belt - took it easy, no overheating). They did diagnosis, replaced the tensioner (with stock pulley, 3" I think vs 4" spec'd by Whipple) and it all looked good to him. I kinda freaked out cuz I've had so much trouble, and told him to go ahead and replace the HB. I got the old HB back, can't see anything wrong with it.

Car drives fine now. I did notice that the belt is riding further away from the engine cover - before it looked way too close to me, maybe even rubbing, which I thought was further evidence the HB had gone bad - like the crank pulley had slid toward the engine.

I am still completely stumped by this whole episode. How could the tensioner be the problem? I had already replaced the pulley on the original tensioner, replaced the tensioner and the pulley, and replaced the bearing in the pulley and tried both new and old tensioner / pulley combinations, with the same results.

BTW how do you tell when a harmonic balancer goes bad, can you see it? That's a very thin strip of rubber in there, it looks intact and I couldn't turn the pulley independant of the shaft (at least by trying to hold the round shaft in a vice which doesn't allow much torque).

I have a theory... the last belt I bought is a Gates RPM, made for superchargers - why not, right? Well I just learned they stretch and flex less, so require less tension, and create a lot less idler motion ...IF... the length / tension is correct. But if tension is too high, belt bucks and slaps and makes the tensioner jump - I think that's what I was experiencing. My guess is, the smaller pulley on the new tensioner (by pure luck) provided the correct tension and voila - all happy again (so far).

But I still can't explain why the belt is back where it should be, riding a good 1/4" in front of the engine cover on the tensioner pulley instead of almost rubbing against it. Oh well, all's well that ends well - fingers crossed!

tabstang said:

I have a theory... the last belt I bought is a Gates RPM, made for superchargers - why not, right? Well I just learned they stretch and flex less, so require less tension, and create a lot less idler motion ...IF... the length / tension is correct. But if tension is too high, belt bucks and slaps and makes the tensioner jump - I think that's what I was experiencing. My guess is, the smaller pulley on the new tensioner (by pure luck) provided the correct tension and voila - all happy again (so far).

But I still can't explain why the belt is back where it should be, riding a good 1/4" in front of the engine cover on the tensioner pulley instead of almost rubbing against it. Oh well, all's well that ends well - fingers crossed!

Click to expand...

A failing tensioner can/will move the belt off-center, and if gets bad enough it will toss the belt. And I would suppose if the HB was in bad enough shape to move the belt off-center, it wouldn't last long beyond that point.