Whining noise coming out from under truck...

[NavyVet88]

I have a 94 Chevy C1500 2wd with a 5.0 350 v8. 208k miles.

I noticed today there was a whining noise coming from under the truck when I let off the gas and just coasted slowly from about 25mph. It doesn't make the whining noise when I accelerate only when I let off the gas and slow down by coasting WITHOUT the help off the brake system.

Idk if it's the torque converter in the tranny or the rear differential? Do you guys have any ideas what it may be?
The tranny has plenty of fluid albeit it needs to be changed and it has a very slow leak.

 

[mk378]

Have you checked the differential fluid?

 

[NavyVet88]

Originally Posted By: mk378
Have you checked the differential fluid?


Negative, that is my next move. It is my mother in laws truck and she gave me the deer in the headlights look when I asked has she ever had the differential fluid serviced

 

[mk378]

Also when you're underneath wiggle the driveshaft to check for bad u-joints. Though that typically won't cause a whining noise, it is something that should be checked with that many miles and lack of maintenance.

 

[Virtus_Probi]

Have you seen the cat lately?

 

[Ga129]

Originally Posted By: Virtus_Probi
Have you seen the cat lately?


+1

 

[Chris142]

Originally Posted By: NavyVet88
I have a 94 Chevy C1500 2wd with a 5.0 350 v8.
Not that it matters but is it a 5.0L or a 350?

 

[NavyVet88]

Also when you're underneath wiggle the driveshaft to check for bad u-joints. Though that typically won't cause a whining noise, it is something that should be checked with that many miles and lack of maintenance.

I can't upload images from my iPhone that I took, but looking at the driveshaft coming from the tranny, it is completely soaked in fluid on the rear of the tranny and the first foot of the driveshaft. I could t find any play in the driveshaft to indicate a worn joint. Like I said, the complete rear of the tranny is hosed in fluid.

I guess this is proof that the dipstick alone isn't a sure fire way of true fluid level because the tranny dipstick has always maintained a full indication of fluid.

 

[NavyVet88]

Originally Posted By: Chris142
Originally Posted By: NavyVet88
I have a 94 Chevy C1500 2wd with a 5.0 350 v8.
Not that it matters but is it a 5.0L or a 350?


5.0L

 

[Chris142]

Originally Posted By: NavyVet88
Originally Posted By: Chris142
Originally Posted By: NavyVet88
I have a 94 Chevy C1500 2wd with a 5.0 350 v8.
Not that it matters but is it a 5.0L or a 350?


5.0L
305 cuin.not a 350

 

[mk378]

That's your slow leak then. The oil seal where the driveshaft goes into the tranny is pretty easy to replace.

 

[jr047]

Chevy 305 = 5.0L
Chevy 350 = 5.7L

For engine sizes, 61 cubic inches per liter is close enough.

 

[NavyVet88]

Originally Posted By: mk378
That's your slow leak then. The oil seal where the driveshaft goes into the tranny is pretty easy to replace.


Would that explain the whining?

 

[NavyVet88]

Originally Posted By: jr047
Chevy 305 = 5.0L
Chevy 350 = 5.7L

For engine sizes, 61 cubic inches per liter is close enough.


I stand corrected sir, as per further research it is a 5.7L. Thanks for the correction.

 

[mk378]

Originally Posted By: NavyVet88
Would that explain the whining?

No, it's just going to make the transmission fluid go away slowly.

 

[jr047]

The sound you describe could be from the rear axle; the loading and contact points on the gears can change when you accelerate and coast. When I changed my rear axle from 2.41:1 to 3.23:1 in the El Camino, I picked up a resonance (manifested as a whining sound) between about 35 mph and 40 mph in top gear. I have aftermarket gears and there's really nothing I can do about it but turn up the radio, but it also isn't very loud. The difference from your situation, is I usually hear it both while cruising at a steady speed, and coasting.

Without hearing it I couldn't venture a guess as to whether anything is really wrong or if it's just a characteristic of that particular vehicle, which it is in my case.

 

[NavyVet88]

Originally Posted By: jr047
The sound you describe could be from the rear axle; the loading and contact points on the gears can change when you accelerate and coast. When I changed my rear axle from 2.41:1 to 3.23:1 in the El Camino, I picked up a resonance (manifested as a whining sound) between about 35 mph and 40 mph in top gear. I have aftermarket gears and there's really nothing I can do about it but turn up the radio, but it also isn't very loud. The difference from your situation, is I usually hear it both while cruising at a steady speed, and coasting.

Without hearing it I couldn't venture a guess as to whether anything is really wrong or if it's just a characteristic of that particular vehicle, which it is in my case.



I honestly can only say the way to reproduce the sound without the truck is to describe it as sounding like an old timey fire engine siren at a very very low volume. My mother in law told me the sound comes and goes in the sense that it could last for a week and you won't hear it again for months at a time. I've personally never heard it until today and I have driven that truck several several times in the last six months.

Not much of a description of the sound but it is loud enough to be heard over flow master exhaust coasting at 25-35 mph

 

[jr047]

From that description I wonder if a bearing is starting to go bad, possibly in the rear axle. Hopefully someone who's encountered something like that will chime in. It sounds like the rear axle may never have had its fluid changed, and it might be worth having a transmission or axle shop look at it.

 

[NavyVet88]

Originally Posted By: jr047
From that description I wonder if a bearing is starting to go bad, possibly in the rear axle. Hopefully someone who's encountered something like that will chime in. It sounds like the rear axle may never have had its fluid changed, and it might be worth having a transmission or axle shop look at it.


Yeah my thoughts as well. Regardless of the sound, the tranny is gotta get fixed for the leak and I'll be sure to inquire about the noise. And as I'm typing this, she tells me that sound has been present for years smh

 

[BAJA_05]

When is the last time you changed the fluid in your rear pumpkin? I blew a rear in a 1980 Dodge Ram doing power brakes back in the day. Put a new rear in it & it made a whining noise until I added the POSI supplement. Strange but true, from there I added it once a year until I sold the truck.