GM alternator hum...

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Skillet

Skillet

Skillet
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Noticed a buzz / hum coming from my GM alternator this weekend when everything is turned off.

It is very subtle and never noticed it before. Thought maybe it was there all along and did not pay any attention to it.

Well, went to start the rig after sitting for a couple of days and the battery is dead.

Now, I went through some of the wiring this weekend and just zip tied, cleaned up stuff, etc...so I don't think it has anything to do with me messing around.

I also researched the hum here on mud and found a couple of items but nothing conclusive.

It is a rebuild GM alternator from O'Reilly with an internal volt reg (I think), but looks brand spanky new.

Before I go swapping it out, any ideas on this?

Wish there were s a 350 / SBC / GM sub-forum so I would not need to keep bugging this section with Chevota crap.

Thanks for any help.
 
It was making that noise with the ignition off? I know you said 'everything', but just checkin....
 
Yup, no key in the ignition and NOTHING on.

Also, I just checked the alternator output with a my multimeter with the engine running and it is showing 10.89 volts at the alernator and at the battery.

This is after it has been idling for 1/2 hour.

Bad alternator?
 
I'd think so. The sound you were hearing was maybe some sort of internal short in the alternator.
 
Poser said:
What happens when you increase engine RPMS to say 1500 to 2000 RPMS?


Anything?
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Unfortunately, I shut the motor off and the battery did not get any charge, then my jumper box went too low to start it up.

I will check it with higher RPM's when I get it started again.

Alternator is humming away...


I also checked a hot lead for the lighter and it was at 10.75 volts.

When I checked that same lead over the weekend, it was almost 13 volts at idle.
 
There are sevaral things you can try after cleaning terminals and what not. Charge the battery, load test it but you don't really have to... not yet, anyhow. O'reiley can test your alternator if you want to go that route. Or after the battery is charged check the voltage. Start it and while it's running check the battery agian, should have 1-2 volts more than when it was off. Turn off engine and disconnect one of the terminal leads, I usaully do the neg. side. check for current flow with a meter or you can do it with a test light. Just connect the test light on the neg. side to battery terminal/cable to complete circuit. Test light should be off if it's on, start disconnecting items until the test light turns off.
 
Does it have just one wire going to it? (The alt). They do need to be rev'ed up to 'turn on'.

Does the humming stop if you lift the pos cable?
 
Skillet said:
So, I was just going to pop the alternator out and have it tested tomorrow, but the tensioner uses a big friggin' torx head that I don't have.

Wonderful...
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Can you post up a picture?


Is this a serpentine belt configuration?
 
Skillet said:
no, not really. was pretty warm after the engine was idling for a while, but I figure that was par for the course.
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An alternator is going to generate heat when it is under load, and trying to charge a dead battery at idle or higher RPMS is going to be asking a lot from it and probably damage it. It is not a good idea to start a vehicle with a dead battery and try and bring the battery back up to a proper level of charge using the alternator.

Hot to the touch:

Warm, you can keep your hand on it is fine; warm to the point that you do not want to touch it or cannot keep your hand on it is not good.

Skillet said:
this is the first 350 I have ever owned or played with, so I hope you guys cut me some slack.
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No worries bud.

:beer:
 
yes, serpentine...


here are some pics...
alt1.webp
alt2.webp
alt3.webp
 
Yea, well...as with everything else, it is probably just a piece of s*** that I need to replace with another piece of s*** that was recommended before it was considered to be a piece of s*** only to be replaced by a piece of s*** that is remanufactured in a s***ty place and will soon be considered a piece of s***...
 
....delivered by a s***ty mailman.

You might be able to rotate that tensioner with an allen wrench that's close to that torx size so you can get the belt off.
 
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