Whine/humming sound under light throttle, some advise?

[Leviticus]

My 1972 C10 with 350/TH350 is making an intermittent whining humming sound when cruising at around 25-30 mph and under very light throttle, like just keeping it running at that speed/rpm.

Its a weird sound, can't quite trace it down yet, almost sounds like the rear end, but it disappears the second you let off the throttle, which doesn't me its not the rear end. But it seems like it would make more noise under more load if it was the RE.

Anyone have any ideas before I start ripping into this thing? I am hoping its not a trans pump/torque converter, never slips and shifts good.

I am going to be replacing or repairing the PS pump, the whole assembly has some wobble to it at idle, just saw it tonight, almost s#%$ my pants when I saw it.

Thanks guys!

[71longbed-brew]

i have a simliar sound .... i know its not the rear end .... mine almost sound like the tranny ... but i've been driving for 7 years and its always done it .... so it must not be too serious (fingers crossed)

[Leviticus]

Hey guys,

Still have this noise and I can't track it down. It likes to do it while cruising through town and almost coasting, but still just barely on the throttle, give it gas and it seems to go away. On the freeway, it does it a little bit, but when you slow down then give it more gas in third kind of bogging it a little it will make the noise as well.

Sounds like you are rubbing a wet finger on the top of a wine glass, type of sound.

I am lost, I just serviced the rear diff today and it seemed good inside, no obvious wear. The fluid was a little brown but you could still see through it. It has all new accessories on the engine, and the tranny fluid seems to be at the correct level.

[Willys47]

the way you discribe it sounds to me like it is the rear gears but I have heard that tranny oil pumps can make a whine like this as well.I know thats no help I would check the diff out and make sure the gears don't need a shim adjustment.

[dznucks]

from what you are describing, i think i have been chasing the same problem. sounds like a very faint humming when you are barely in the throttle, but not quite decelerating.

i am pretty sure its either the tranny gears or the rear end gears.

the gears have alittle play in them, especially older rear ends and trannys. I think its this little bit of play that is casuing the whine. for instance, if you jack up your rear end, hold the drive shaft and/or put the truck in gear, then rock the tires back and forth. Thats the play I am talking about.

When your engine is pulling, the gears are meshed all the way one way against one surface of the gear teeth. when you are slowing down, in gear, the gears are meshed the other way on the opposite face of the teeth. when your barely coasting, these gears arent meshing all the way agaisnt each other. so you get a high frequency chatter or vibration from wear on the teeth surface and edges.

i could be totally wrong, but those are the only rotating assemblies, that would cause this noise, that havent rebuilt on my truck.

[TomJohnston]

You could try a couple of things:

turn up the radio! (ala click and clack)

put glass packs on!

lame, I know

[gonzo6869]

I am having the same problem as well. I also get a loud whining noise if I put it in first gear, bring it up to about 2500 and then decelerate.

[dan42]

Do you have a two piece drive line?

[gonzo6869]

Me, I don't think I do.

[Leviticus]

Originally Posted by dan42

Do you have a two piece drive line?

Yeah, I have the two piece. I was wondering if maybe it was the Carrier Bearing maybe. I need to find a driveline shop and have them replace it and my u joints cause I am sure they are due.

[Leviticus]

Originally Posted by dznucks

from what you are describing, i think i have been chasing the same problem. sounds like a very faint humming when you are barely in the throttle, but not quite decelerating.

i am pretty sure its either the tranny gears or the rear end gears.

the gears have alittle play in them, especially older rear ends and trannys. I think its this little bit of play that is casuing the whine. for instance, if you jack up your rear end, hold the drive shaft and/or put the truck in gear, then rock the tires back and forth. Thats the play I am talking about.

When your engine is pulling, the gears are meshed all the way one way against one surface of the gear teeth. when you are slowing down, in gear, the gears are meshed the other way on the opposite face of the teeth. when your barely coasting, these gears arent meshing all the way agaisnt each other. so you get a high frequency chatter or vibration from wear on the teeth surface and edges.

i could be totally wrong, but those are the only rotating assemblies, that would cause this noise, that havent rebuilt on my truck.

This makes sense, I wonder if it is it. Let me kniw if you figure anything out and I will do the same.

Thanks

[Mr Pops]

I had the exact same symptom on my 02 Suburban with over 300,000 kms on it. I went and got the rear diff rebuilt and the ALL the noise is gone.

['72customdeluxe]

my diff does that, maybe just the way the gears mesh under that amount of load. I know first gear in my th350 is loud

[420am]

Carrier Bearing on all of these trucks I'd guess.

Check it before you tear into the rear end.. like I did. lol

[Leviticus]

Originally Posted by 420am

Carrier Bearing on all of these trucks I'd guess.

Check it before you tear into the rear end.. like I did. lol

Did you have this same sound when your carrier was going out?

[dznucks]

one piece drive shaft on mine.

[Wrenchbender Ret]

Sounds like rear end noise to me. Take hold of the pinion flange & see if there is any up & down play in it. Slack when you turn it is normal but it should not have any brg. loosness. Pull the cover. There should not be any side to side play in the carrier.

[gonzo6869]

Originally Posted by '72customdeluxe

my diff does that, maybe just the way the gears mesh under that amount of load. I know first gear in my th350 is loud

The noise your talking about in first gear, is it only when you decelerate. My TH350 dose the too, almost sounds like a blower.

[Hx16457]

Mine is doing this too!
I have it in the air and I am turning the drive shaft by hand.
The whining is coming from the tail shaft area.
I am going to pull the speedo cable and then the speedo gear!
Then recheck if stays I will pull front u joint to ensure it is not radiating from the dif.
Then turn the yoke by hand see if it stays....
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[Ol Blue K20]

I've heard stories from old GM techs that 67-72 was famous for the hood hinge springs humming under differing conds on different trucks. They said it drove them crazy until service bulletin came out on it. Stuff the springs with a piece of foam rubber and see if this helps (GMs tech suggestion).

[TBONE1964]

First, what gear is the trans in at 25 - 30 mph? Has it shifted in to 3rd gear yet? Try and drive it in low gear at the same speed and see if it makes the same noise. If it makes the same noise at the same speed regardless of the gear, then I would not suspect the trans is the problem since you are changing the rpm's.

How many miles would you say the rear diff has on it? From what you describe the first thing I thought was the ring gear is wearing out of spec on the drive side. When the ring and pinion wear, the back lash gets looser and gap between the pinion and the ring gear increases. It also puts the relationship between where the ring and pinion mesh in a different spot. That will cause a noise under a slight load.

Do you know how to check the wear pattern on a ring gear? If you get the cover off and look at it, the pattern should be fairly close to the center of the ring gear tooth on both sides. They make a compound for checking gear patterns that you could by from a transmission parts supplier.

This can get rather involved but there is hope. If you can get your hands on a good GM service manual, all of this is explained in detail and how to correct it.

Keep us posted.

[c10monkey]

Mine does this as well. Found out from a retired mechanic that when the bushings in TH350 wear down , the gears become a little loose and creates this sound. He said that it doesnt really hurt anything and not to worry about it. He said only way to get rid of it was to rebuild... $$$$$ . But he also told me if I had it rebuilt to tell them about the whine to make sure they shim it correctly.
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[1972SUPERSB]

I have this same sound as well. I was thinking it was the trans as well. As long as it doesn't hurt anything i will leave as is
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[Square_78]

My 1970 GMC does the same thing. Its constant with different engine RPM and does it under load or coasting, but louder under load. I am assuming its the rear end. Im going to change the fluid and hope it goes away... although it does honestly sound kinda cool like a quiet blower under the hood.

[Helipilot17]

its your diff, mine does the same thing under slight load, just the way the crown and pinion are meshing inside the case. you can try to shim the pinion however it will only get marginally better, but will never go away completley