8 3/4 womp womp womp noise...

Hey I just started hearing this womp womp womp noise which I think is coming from the rear. Its a 8 3/4 489 with 2.76 gears. This is a 74 barracuda. I had this out last year and drained all fluid and the inside was pretty clean. I re-filled with lucas 80/145 gear oil. I was only able to fit in 4 pints, the service manual says 4.5 pints. Is it possible that there isnt any oil in the axle shaft area?
I have only been driving this for about 5 weeks and only put about 30 miles on it since filling it.
This noise just started soon after installing new wheels and tires, and so I thought that was the problem, because it sounds like its in step with the rotation of the wheels. I put the old wheels back on and it still makes the noise.
Thanks.

no not from that. Sure sounds like tire/wheel tho. Nothing else was swapped/altered back there? EDIT you might put the rear up on stands/take off tires/wheels & idle it in gear & see if you hear anything (dont forget to hit the brake to stop rotation before going back to park!) & dont forget the lug nuts back on (3 on each side)

Sounds like a tire issue or bent wheel to me too.

No, nothing else changed. The only that really changed is the local temp, we are in the 95 plus zone.
I still have the old tires on, maybe I will test drive it some more to confirm.

I have it jacked up on stands, what should it sound like when I spin the wheels by hand? It sounds and feels slightly like a rotary phone, if that makes sense. (in park).

I think I would check the rear wheel bearings on the outer end of the axles. The noise you describe is consistent with a failing wheel bearing. You can pull each axle out and manually inspect the bearing for pits/wear/discoloration.

The bearings are suppose to be greased (they are part of the maintenance procedure that very few follow) by grease similar to what you grease the tie rods & ball joints with. (Unless you have the sealed "green" bearings.) There is a seal between the axle tube and the bearing, if it failed and allowed the axle gear lube to wash the grease out of the bearing, the bearing will be short lived.

If you have never had the 8 3/4 axle bearings re-greased, this might be a good time, and replace the seal now as well.

Pull off the rear wheels & brake drums, remove the 4 nuts that hold the axle to the housing (through the hole in the axle shaft with a socket), pull the axle shaft out of the housing (sometimes to have to jerk it pretty hard) and be sure you clear the e brake bar as the bearing comes out of the axle tube. Be careful not to allow the axle to drag across the seal (if you don't intend on changing it). You can insert the axle in far enough to use it to wedge the seal out of the housing if you are replacing the seat, be careful not to damage the end of the axle on the housing. If the bearing is defective, it will need to be pressed off & the new one pressed on. If you replace the bearing, replace he inner seal as well. Gene

Axle shaft bearing. Never heard a bent rim make that noise.

R

Axle end play set right?

Thanks everyone. I took the rear axles out and they were wet from the differential fluid leaking in. Also END PLAY was way out. I replaced the bearings with the original taper style and replaced both inner and outer seals. I set End Play and drove about ten miles and then reset it again, it moved from .010 to .035. I just checked it again after about 100 miles and its good.
Its interesting that it happened three days after I installed new wheels and tires. I guess some things are just coincidental.