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Old 09-22-2020, 08:20 PM   #1
johnny
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Default 38 ford alternator

Have a 38 ford changed to 12 volt with alternator .The fan bolts to the pully on the end of the alternator .Special pully used .Trouble is ,there is a high pitched whine from the alternator .Have changed bearings ,used a larger front bearing thinking it was the bearing .Also thought the fan was puling the armature ahead into the bearing. Made sure the fan blades were running true. After all this, still no better .But disconnect the feed wire, The whine is gone. We now think there is some kind of electrical resonates causing the whine .So any suggestions to take the whine away.
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Old 09-22-2020, 09:10 PM   #2
cadillac512
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Default Re: 38 ford alternator

Have you had the alternator tested for correct output? Reason I ask is because a bad diode can cause a distinct whine in an alternator but also reduces the output. A shorted stator winding can do the same.



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Old 09-22-2020, 09:34 PM   #3
koates
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Default Re: 38 ford alternator

As stated above one diode may be faulty out of the six main diodes inside. That will create a phase inbalance which creates a whine. If an alternator is charging at a high rate it can also make a whine. You need to check the voltage at the main terminal with some revs up and this should read around 14 volts. Also check what amps it is charging. I suggest you take it to an auto electrical shop so that they can run it up in their test bench. They would also have a diode load tester that can test each individual diode. Regards, Kevin.
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Old 09-23-2020, 09:40 AM   #4
cas3
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Default Re: 38 ford alternator

alternators whine from the load on them. the more it is charging (load) the more it whines. normally, just after you start it, it has a heavy load to recharge the battery from using the starter. if the system is all good it should quiet down after the battery is back up to full charge. it will always make some noise, but not what it does under full charge mode. if its always loud, you may have a weak battery which make the alternator think its job is never done. could be regulator bad too. got any accessory's running all the time?
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Old 09-24-2020, 02:15 AM   #5
Kurt in NJ
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Default Re: 38 ford alternator

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go to one of the auto parts stores , some will "test" battery and charging system, usually part of the test will be a diode test, "ripple" or ac mixed with the DC reading
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