Differentiate: Alternator, or belt or pulleys?

I posted this once before, but not really good answers.
Old dodge van mid 70's, 318. Alternator had spacer that one bolt slipped in.
Long time ago I lost the spacer and used washers to align the pulleys
with the bolt alone.
Worked for a long time.
Now: LOUD squealing on startup, when engine warms up, squealing goes away. Squealing ONLY occurs simultaneously with alternator gauge needle bottoming out in charge position, alternating with normal position, in which case squeal disappears-i.e. as long as needle swings back to midrange position squeal disappears, only to reappear when bottoming to charge position. Squeal and bottoming of needle go away completely when motor warms up.
Checking the belt it is one of these kind that has teeth on inside pulley side surface. Belt looks ok-not worn; appears undamaged, but is somewhat loose about 3/4 to one inch deflection.
pulleys SEEM to be aligned correctly eyeball check only.
How do I differentiate between a squealing alternator versus a squealing loose belt vs a squealing out of alignment pulleys? What is causing the alternator gauge needle to bottom itermittently to full charge, swinging back an forth between that and midline reading-is this a function of a bad voltage regulator?
I cannot run this thing too long as my neighbors will complain about the noise.
I wish to avoid replacing a $100 alternator if that is not the cause.
How do I differentially diagnose the cause of the problem. Anyone? Thanks.
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On Sun, 22 Jul 2007 01:05:05 +0200, repeat wrote:

If your alternator bearings were going, they would squal all the time. What you appear to be describing is belt squeal. Check the alignment carefully, but I bet the belt is gone. Even though it looks good, it may be shot.
Try a new belt; they're cheap enough. And the reason it squeals more when the charge guage is low is that the alternator is putting more of a load on it.
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You're taking something simple and making it WAY too complicated. Tighten the belt and see if the noise goes away -- as it probably will. If the belt has been loose enough to upset your neighbors you should replace it. After the new belt has been run a little while, re-adjust it.
Don www.donsautomotive.com
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Ok, thanks for the replies, but still no answer to the core question. Maybe there is no way to differentiate a squealing alternator from a squealing belt/pulleys out align, except by process of elimination. Do the alternator tests test for bad bearings in the alternator? I kinda like to find the problem and fix in one step, if possible.
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repeat wrote:

If you remove the belt and spin the alternator by hand, you should be able to tell quickly whether the bearings are OK or not. If it spins smoothly and quietly, it's probably not the bearings that are your problem.
nate
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repeat wrote:

I've owned a lot of cars. I've had a few cars with squealing belts. In only one instance it was the alternator itself. In all other cases, it was a worn or glazed belt. A belt is also way cheaper than an alternator, so I would start with that.
FWIW, I had one car that was a real PITA with squealing belts - IIRC I ended up using the house brand from a local parts store because every other brand just squealed - just one of those minor differences between the brands.
Ray
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repeat wrote:

'Normally' when the bushing or bearing goes out on the alternator it causes a 'lot' of heat really fast so if you start it up and the alternator gets really hot, suspect the bushing.
I test the belts by taking a cold off engine and seeing if I can hand spin the alternator pulley under the belt. If I can do this, it will slip under load for sure and likely make noise unless it is polished up which happens on our off road Jeeps from mud (liquid sandpaper).
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id !15147590 (More Off Road album links at bottom of the view page)
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repeat wrote:

While I agree with the other posters about "just tighten it up" or "replace the belt and tighten it up" it may not be that simple. While you're at the parts store getting a new belt, have the alternator checked.
Hmm... I never considered this before. Could one say, convert an old vehicle like the one we're discussing to a modern serpentine belt system by stealing the complete accessory rack off the front of, say, a Magnum 5.2 motor? Did the bolt points change over the years? I sure love the auto-tensioner, and if you're already in need of an alternator and the AC is out (you'd be getting an r134a pump out of the deal) it likely wouldn't cost that much more in parts at the local pull-it-yourself junkyard.
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If you are converting a v-belt system to a serpentine system, check the rotation direction of the accessories. Anything that runs off the back of the serpentine belt (like the water pump) rotates the opposite direction.
--
Ken




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In responce to Nosey 's post. I thought everyone should know:

there are serp belt conversion kits avail for the 5.2 and 5.9 L engines i'll look in some of my catalogs laying around and see if i cant find you a good part number/source. i forget how pricey they are though.
--
Chris

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repeat wrote:

It sounds very much like something somewhere is shorting, placing a heavy load on the alternator and making it drag really hard on the belt. The deflection you mention doesn't sound abnormal, but might be just enough to let the belt slip a little (and make lots of noise) when the alternator is under full load.
It's also possible the voltage regulator is failing, putting full field current on (which puts the alternator on full output, which squeals the belt, etc. etc.). That's probably more likely than a full-out short on the alternator output (which is, of course, also the battery positive).
It could be the alternator itself shorting. Very worn brushes or an intermittent diode could be the cause. This isn't very likely.
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