rear end whine (?)

[SethM]

OK, maybe its a "roar" not a whine. The back story: My daughter lost the tranny in her beloved 85 T4WD and that prompted me to reexamine fluid levels in both my tranny and rear diff (I also have a 85 T4WD). Almost immediately after adding gear oil to the diff, I notice a whine/roar coming from the rear (and I think passenger side) of the car. Now, it may be completely coincidental that the noise started after I added the gear oil-- I'm just providing the facts as I know them. The noise has become somewhat worse since and I am trying to limit my driving while I try to sort out what is going on. I took the car to my local backyard mechanic who I go to when I'm in over my head/knowledge base and he put the car on his lift. When I spun the right rear wheel, we could definitely here the noise but it does not seem to be coming from the wheel area itself and thus we are not thinking its a wheel bearing but rather coming from somewhere inside the diff. So a question to those of you who really know these cars, is there a bearing or gear we should be looking at? My friend thinks it may be more likely to be a bearing because when on a road test, it does not seem to make a difference if I suddenly let off on the gas--- he said gear noises generally change/stop when "unloaded" whereas a bearing noise will continue. Any diagnostic help from all of you is greatly appreciated.

[rer233]

My vote is wheel bearing.

[dlb]

when you hear hoof beats, think horses, not zebras: it's not likely changing the gear oil had anything to do with it, and it's not likely your diff suddenly went bad despite having plenty of gear oil. roaring/whining/growling from the back end is usually wheel bearings so that also gets my vote.

another way to determine which side is bad is to have someone drive the car while you ride in the cargo area. put your ear down towards either side and you should clearly be able to tell which side it's coming from. this bonehead technique has worked well for me in the past.

[xirdneh]

i am in for wheel bearing too

[SethM]

OK, will take another look focusing on the wheel bearing. It is definitely coming from the right hand side. Thanks for the responses.

[lannvouivre]

I would remove the rear wheels and brake drums, then just spin and turn the rear hubs by hand...uh, I guess with the driveline unbolted. They should be smooth and silent.

[xirdneh]

turning the rear axle while it is still installed will produce noises from the differential that are normal sounds
unless the bearing is real bad you might not be able to tell if the bearing is going bad
its best to pull the axle and support axle by bearing in one hand and spin axle with other hand
it should be smooth and quiet
if it is bad you will know it