Transmission humming noise between 40-50 mph

[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.