Singing Alternator - '95 Crown Vic

Hi Folks- Every time I have heard this noise in the past it meant a shorted diode and a soon-to-be kaput alternator. I had one once go up in a plume of smoke.
Problem is, it doesn't always make the noise. Of course, it sings more at certain engine speeds but sometimes it is not there at all.
I put a digital volt meter on and have over 12.5v first thing in the morning. As soon as I start it, I get 14.4v and, after a while, I see 14.5 or so. Turning on the lights drops it to 14.1. In other words, other than the noise, no symptoms. I plan to clean the battery posts in a minute, just because it hasn't been done in a while. Any other ideas?
Thanks!
PoD
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Paul of Dayton wrote:

Mines been doing the same thing for about 6 months ... let me know what you find.
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Is it kind a mid-tone pitch that only happens at idle with lights on? If so, mine does the exact same thing and has been that way since the day it rolled off the lot almost 7yrs, and 113,000mi ago. Without hearing it exactly, I would say its normal. Mine only does it when under heavy load but there is nothing wrong with it. If I turn the lights off, the sound goes away.
Ford Tech
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The noise doesn't change with or without the headlight load. Oddly, it doesn't do it right after a start when the load to recharge the battery is heavy. Cleaning the battery posts had no effect. The battery is NOT new but seems strong.
I'll let you folks know what I find. I guess I could take it off and have it checked at a shop but I will wait for the temps to warm a bit. It's below zero right now.
Thanks!
PoD

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PoD,
One thing you can do to check out the alternator is take the car to a shop with a VAT 40 starter/chargeing system tester. They can do a load test on the battery, and the alternator. That will endicate if its bad or not, then they should be albe to put an osciliscope on the alternator to see if the diode bridge is bad or not.
Ford Tech
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How many miles are on the car in question?
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about 172k miles. Since cleaning the battery posts I have heard the whine only once. Today my 30 mile commute was quiet and the voltage was a few tenths higher than before.
PoD

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Paul of Dayton wrote:

That's great Paul. But at 172K you might want to think about replacing the brushes (brush holder asy) and the Voltage Regulator soon, just because of the time and mileage . It's about a $40 or less investment into a $175 alternator that hasn't yet failed, but is due to at any time. If the bearings aren't noisy and it's not "singing" due to bad diodes, it might be the best ~$40 you ever spent on that indestructible Crown Vic for prevention. Those brushes are usually good for ~125-150K miles. When the brushes get too small they take a quick trip around the windings causing all sorts of unrepairable havoc to the alternator. Yer on borrowed time there buddy, those brushes are getting thin.
You can do the brush holder for about ~$20, but Murphy says that the voltage regulator will fail in the middle of a rain\snow storm or otherwise inopportune moment shortly after you do the brushes. I recently went through this same scenario on my 150K mile Mark VII. Replace the regulator while you're there.
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Thanks Tom. I figured it might be about time for an overhaul. The kit I looked up has all the parts you mention as well as new bearings. I think it was about $40. I've rebuilt alternators before, been driving Fords since 1972. I will pray for a warm spell or maybe just pull it this weekend and do it indoors.
PoD

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I bought an alternator rebuild kit from this guy (below). He has a kit for most every Ford alternator.
http://stores.ebay.com/AUTO-REPLACEMENT-PARTS-INC_W0QQcolZ4QQdirZ1QQfsubZ0QQftidZ2QQpZ2QQtZkm
Paul of Dayton wrote:

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Fordfan wrote:

http://stores.ebay.com/AUTO-REPLACEMENT-PARTS-INC_W0QQcolZ4QQdirZ1QQfsubZ0QQftidZ2QQpZ2QQtZkm

in to come on when car started. This causes speakers to whine and hard to pin point cause. Inadequate filtering of your alternator under load. A properly / well installed filter by professional will usually fix it. You have to know how to fit it otherwise it will not work. Your complaint of whine when turning of headlight is the clue for me. Had a Honda did the same thing. Had me beat till I fitted a better filter.
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