Why does my Alt hum? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Russell · 08-27-2005, 01:42 AM

Hey all!

I've got a newer style alternator in my truck, as it has serpentine now. I have it hooked up as follows: Thick wire is hooked up to the big post, which goes straight down to the battery, thin voltage sensing wire is hooked up to the old red wire, and the brown idiot light wire is hooked up to the old brown wire through a 75 ohm resistor as I was told to do. The alternator charges like it should when the engine runs (14.9 volts on the nose) but when it is just sitting there, the alternator makes a noticeably loud humming noise. Anyone have any ideas what it could be?

a28doc · 08-27-2005, 05:19 AM

is the belt too tight? sometimes it puts torque on the shaft and bearings causing a hum... other than that not sure
Doc

**N2TRUX** · 08-27-2005, 10:09 AM

Quote:

Originally Posted by Russell

.... but when it is just sitting there, the alternator makes a noticeably loud humming noise. Anyone have any ideas what it could be?

Maybe it's happier when it hums?

Maybe your truck wants to be a Hummer?

Maybe it wants a Hummer

What do you when it's just sitting there. Are you saying it does this when the truck is not running?

hotrodhomi · 08-27-2005, 12:17 PM

Is it the alternator making the noise or are you getting feedback through the stereo?

**AspecialZ** · 08-27-2005, 01:45 PM

Maybe it dosen't know the words...

good luck though seriously.

bodydropped · 08-27-2005, 05:19 PM

my moms burb does that it comes and goes but its been like this for years it sounds funny thou

Russell · 08-27-2005, 05:52 PM

It hums when the truck is sitting, not running :P

If I unplug the brown wire, and voltage sensing wire, the humming immediately dissapears. Its an electrical hum, and is too quiet to be heard when the engine is attempting to run (TPI needs a bit of work, lol)

Justins76 · 08-28-2005, 03:46 AM

I usually get a high pitched humm when there is a large load on the alt, like right after starting when its trying to recharge the batt after sitting for awhile.

Russell · 08-28-2005, 11:50 AM

yeah, I could understand that, but this is while the truck is not running, and just sitting in the shop. Ignition off, nothing on at all.

86swb · 08-28-2005, 04:56 PM

[QUOTE=N2TRUX]Maybe it's happier when it hums?

Maybe your truck wants to be a Hummer?

Maybe it wants a Hummer

QUOTE]

Or maby he needs to leave his radio off. No music- maby the humming will stop. I'm sorry, I know, we are bad. But really, do not know why it likes to hum.

Never had that happen.

Russell · 08-28-2005, 06:01 PM

lol, if only my truck actually had a radio...

bodydropped · 08-28-2005, 10:12 PM

my dad said ur diodes in the alt are back feedin and thats not a good sign

Russell · 08-29-2005, 12:13 AM

Whats the best way to stop the feedback? As I mentioned earlier, the alternator works perfectly when the truck is actually running.

If its bad diodes, I've got a very similar alternator that has a bad set of bearings on it that I can replace them with.

bodydropped · 08-29-2005, 11:50 AM

u can get someone to take the 2 and build u one

86-C10-V6 · 08-29-2005, 08:54 PM

I just had an alternator tested and it had a bad diode, it didn't hum though and it was putting out about 15 volts.
14.9 Volts is really too high, it should be around 13.8.

1976K5CHALET · 08-29-2005, 10:31 PM

Its probably a bad diode. You don't see it happen very often but i have had it happen to me once before.

DW

08-27-2005, 01:42 AM	#1
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Why does my Alt hum? Hey all! I've got a newer style alternator in my truck, as it has serpentine now. I have it hooked up as follows: Thick wire is hooked up to the big post, which goes straight down to the battery, thin voltage sensing wire is hooked up to the old red wire, and the brown idiot light wire is hooked up to the old brown wire through a 75 ohm resistor as I was told to do. The alternator charges like it should when the engine runs (14.9 volts on the nose) but when it is just sitting there, the alternator makes a noticeably loud humming noise. Anyone have any ideas what it could be? __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

08-27-2005, 05:19 AM	#2
a28doc '87 V20 4x4 Join Date: Jun 2004 Location: South Western Ohio Posts: 1,073	is the belt too tight? sometimes it puts torque on the shaft and bearings causing a hum... other than that not sure Doc __________________ '86 K5 Blazer 4x4 FOR SALE '87 v20 4X4 '99 S10 Blazer 4X4

08-27-2005, 01:45 PM	#5
AspecialZ Street Rod Restoration Join Date: Jan 2004 Location: Wellsburg, WV Posts: 882	... Maybe it dosen't know the words... good luck though seriously. __________________ Follow me on Instagram @ hot_rod_shop

08-27-2005, 05:19 PM	#6
bodydropped Registered User Join Date: Jan 2005 Location: beaumont,tx Posts: 757	my moms burb does that it comes and goes but its been like this for years it sounds funny thou __________________ http://img.photobucket.com/albums/v5...ropped/sig.jpg

08-27-2005, 05:52 PM	#7
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	It hums when the truck is sitting, not running :P If I unplug the brown wire, and voltage sensing wire, the humming immediately dissapears. Its an electrical hum, and is too quiet to be heard when the engine is attempting to run (TPI needs a bit of work, lol) __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

08-27-2005, 12:17 PM	#4
hotrodhomi Registered User Join Date: Apr 2004 Location: Sacramento Posts: 3,737	Is it the alternator making the noise or are you getting feedback through the stereo?

08-28-2005, 03:46 AM	#8
Justins76 OutOfMyMind & I'llNeverKnowWhy Join Date: Apr 2004 Location: Another world, some other time Posts: 672	I usually get a high pitched humm when there is a large load on the alt, like right after starting when its trying to recharge the batt after sitting for awhile. __________________ -Justin-Out of my mind and I'll never know why 1976 Chevrolet Silverado C10 350 4bbl / TH350 Big10 longbed 1986 Pontiac Firebird T-Top 5.0L TPI 700R4 WS6 1992 Pontiac Firebird T-Top 5.0L TBI 700R4 My cardomain page I don't like to save, it's more fun to spend!! Last edited by Justins76; 08-28-2005 at 03:47 AM.

08-28-2005, 11:50 AM	#9
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	yeah, I could understand that, but this is while the truck is not running, and just sitting in the shop. Ignition off, nothing on at all. __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

08-28-2005, 04:56 PM	#10
86swb Born a Chevy Man Join Date: Apr 2005 Location: Navarre, Florida Posts: 10,221	[QUOTE=N2TRUX]Maybe it's happier when it hums? Maybe your truck wants to be a Hummer? Maybe it wants a Hummer QUOTE] Or maby he needs to leave his radio off. No music- maby the humming will stop. I'm sorry, I know, we are bad. But really, do not know why it likes to hum. Never had that happen. __________________ John or 86 (Viet Nam combat Vet-BIG RED ONE) '65-'66 1986 Chevy SWB Silverado 1984 Chevy Longbed Silverado New Kia Sportage (Wife's car and she loves it) CHEVY, American made w/pride! If you can read this, YOU NEED TO THANK A TEACHER! If you can read this in ENGLISH, PLEASE THANK A SOLDIER! GOD BLESS AMERICA AND BLESS OUR FIGHTING TROOPS Last edited by 86swb; 08-28-2005 at 04:57 PM.

08-28-2005, 06:01 PM	#11
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	lol, if only my truck actually had a radio... __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

08-28-2005, 10:12 PM	#12
bodydropped Registered User Join Date: Jan 2005 Location: beaumont,tx Posts: 757	my dad said ur diodes in the alt are back feedin and thats not a good sign __________________ http://img.photobucket.com/albums/v5...ropped/sig.jpg

08-29-2005, 12:13 AM	#13
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Whats the best way to stop the feedback? As I mentioned earlier, the alternator works perfectly when the truck is actually running. If its bad diodes, I've got a very similar alternator that has a bad set of bearings on it that I can replace them with. __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

08-29-2005, 11:50 AM	#14
bodydropped Registered User Join Date: Jan 2005 Location: beaumont,tx Posts: 757	u can get someone to take the 2 and build u one __________________ http://img.photobucket.com/albums/v5...ropped/sig.jpg

08-29-2005, 08:54 PM	#15
86-C10-V6 Shadetree Mechanic Join Date: Oct 2002 Location: Youngsville, NC Posts: 100	Bad Diodes I just had an alternator tested and it had a bad diode, it didn't hum though and it was putting out about 15 volts. 14.9 Volts is really too high, it should be around 13.8. __________________ Dave M. (Hacksaw) 86 C10 Scottsdale LWB, 4.3L, Edelbrock 1904, K&N, 700R4, 3.08 Auburn Performance 89 GMC S-15 Extended Cab 4x4, 4.3L, FI 98 K1500 Xcab, 5.7L, 3.43 Gov-Lok

08-29-2005, 10:31 PM	#16
1976K5CHALET Senior Member Join Date: Jan 2003 Location: Grand Junction, Colorado Posts: 610	Its probably a bad diode. You don't see it happen very often but i have had it happen to me once before. DW __________________ Doug Wright aka K5NUTT over @coloradok5.com Owner of http://groups.yahoo.com/group/ChevyK5BlazerChalets Certified K5 Nut



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