Transmission humming noise between 40-50 mph

[Modoyadney]

Hi all,
Had my first longer test drive with my 99 Suburban today and unfurtnately I noticed a humming noise which must come from the transmission.

It occurs between 40-50mph and is the loudest when cruising. As I accelerate it gets quiter or dissapears if I put the foot down a little more.
If I don't step on the gas pedal, it also gets quieter or disappears....

Overdrive seems to have nothing to do with it, because there no difference between driving in D-Overdrive or put in regular Drive (3).
ATF level is full.

 

[Modoyadney]

I also noticed that the ATF color is clear bright yellowish. I've heard from some people that there are oil manufacturers that don't stick to the color coding, but I'm gonna change the transmission fluid next week anyway.
Just hope that if it was a wrong ATF, it didn't do too much damage...

 

[Blackcar]

Transmission fluid should be red in color. Yellowish sounds like engine oil.

 

[mikeyss]

Could it be the rear pinion bearing going bad in the rear axle?

 

[Modoyadney]

Could it be the rear pinion bearing going bad in the rear axle?

After I drove the truck again, to figure out where exactly the sound comes from, it sounds like it would be the middle of the car.
It doesn't sound like it would be in the rear, but I'm not 100% sure.
It starts around 45mph and is the loudest at 50mph. it's completely gone at 60mph and more...
When I step off the gas pedal, it definitely disappears.

I changed the rear axle fluid last week and didn't see anything suspicious in there.
Transmission fluid will be changed next week.

The pinion bearing is a ton of work to replace, isn't it?

 

[exp500]

If you are 4x4, change Tcase fluid and inspect old for excess Glitter.

 

[tom3]

Yes the pinion bearing is, but if the lube/fluid was nice and clear I'd say the noise is not back there. Never seen yellow transmission fluid in a GM product.

 

[Modoyadney]

It's a RWD.
The color worries me a little, but I will replace it as soon as the new filter arrives with regular Dexron III.
At least it doesn't smell weird and seems to have the viscosity of a regular ATF...

Is there any way to properly check the pinion bearing. Wouldn't it become louder and louder as speed increases?

Thank you all for the help.

 

[mikeyss]

I'm not sure how to check for the pinion bearing. I remember when I had my 05 Tahoe, at around 40 mph it sounded like someone blowing air across the top of a glass coke bottle. I replaced the rear axle, and the noise was gone.

 

[Eman85]

You can grab the pinion yoke and try to move it to feel for play but if it had play you'd have really heard it. Pinion bearing will usually make noise on either accell or decell but it will be consistent and speed doesn't matter as it's the force applied to the bearing from the pitch of the gears that makes it noisy. Yellow fluid in the trans is different. Some use hydraulic fluid instead of trans fluid, why? I have no idea but they do. Different theories like a lot of things you'll see in auto repair. Transmissions usually don't make a humming noise, I'd say rear if I was guessing.
Pinion bearing is a little bit of a pain as you have to install and crush a new crush sleeve.

 

[Fless]

Isn't Dexron VI compatible with Dexron III, or do these transmissions require the older spec fluid?

 

[Modoyadney]

Next week I will take a closer look at everything underneath the car and especialy feel for play at the pinion yoke.
I just hope for the best.

Thank you all for the responses. I will update any news here, maybe it will help other peopel too.

 

[Eman85]

Isn't Dexron VI compatible with Dexron III, or do these transmissions require the older spec fluid?

Yes the new fluids are backwards compatible. I usually just use Dexron/Mercon Valvoline or Supertech fluid for a daily driver. Might up to Dexron VI or Valvoline Synthetic for a tow vehicle or race transmission.

 

[Modoyadney]

So, I drove the truck onto ramps today to check for play. I didn't notice anything bad at the diff. It has some play in the directions in which the driveshaft turns forwards and backwards, but i think this is normal.

But i noticed some play in the driveshaft on the transmission side. I took a video of both ends.
This is the rear:

I think there is nothing abnormal here.

And this is at the transmission. Could this be a bad U-joint??

 

[Blackcar]

To me it looks like tail housing is moving with drive shaft you might check rear transmission mount.
Did you have transmission in neutral when checking rear diff for play in the way it turns.

 

[Modoyadney]

To me it looks like tail housing is moving with drive shaft you might check rear transmission mount.
Did you have transmission in neutral when checking rear diff for play in the way it turns.

OK, I will have to take a closer look on the transmission mount, but I think i felt some play in the U-joint as well.

The transmission was in park with the parking brake applied.

 

[exp500]

Jack the rear, put on stands, shift to neutral, then re-inspect. Rotate driveshaft several times while looking and feeling.Test Pinion by pulling and pushing as well as axial play.

 

[Modoyadney]

Jack the rear, put on stands, shift to neutral, then re-inspect. Rotate driveshaft several times while looking and feeling.Test Pinion by pulling and pushing as well as axial play.

I jacked the rear up and checked it in neutral again today and can tell that the pinion yoke definitely has no play at all in any direction.
The U-joints, especially at the front have a little play. I will order new one and repalce them.

In addition I noticed a couple of other things:
The rear wheels have some up and down but no left and right play on both sides, I am not sure if that's normal.
Rotating the driveshaft in clockwise direction is much easier than counterclockwise.
And the piece of the driveshaft that goes into the transmission has some up and downplay, which can be seen/heard in the second video i have linked. Should it be like that?

 

[Modoyadney]

New u-joints are in. The nosie is still there...
Took the brake drums off to have a close look at the play in the rear axle and there is definitely up and down play.
I will order new rear wheel bearings and see what happens...

Is a little up and down play at the rear wheels normal?
Since I will have to take the diff cover off for the rear bearings, is there anything I can check and look for too see if maybe the pinion bearings are bad?

 

[exp500]

If rear Pinion bearing were bad you would have felt play or "notchiness" as rotated. Last check is Sparkly diff oil. If rear axle Bearings worn, axles may be worn also, inspect carefully. When axles removed, remove driveshaft so you can rotate pinion for a good look at it. Bright light and mirror helps alot.
Were U joints original? If not, clocking of shafts could be the problem with vibration(180) out. With axle play likely not, at least not yet in this chase. Hope your repairs go easy.