Changing bearings on rear diff?

[SevenW]

Hi newbie alert here.
I have had my sprint blue 00 manual 6sp S4 for 2 years now. I bought it off a friend who has trouble shot a lot of problems, he had it for 5 years prior, it's done 120k kilometers so far.
From day one when my friend owned it there was always a faint woooooing sound coming from the rear, all 4 wheel bearings were changed about 4 years ago, but still the sound is still there. Fast forward the sound hasn't gotten any louder no shunting of the drivetrain, have changed the diff oil twice, but the sound is still there.

Recently I bought some stuff from ECS and I thought I'd get two new bearings for the diff:

Part#113517185C Tapered bearing
Part#016409123 Tapered bearing

I'm based in Hong Kong, and I've asked around to see if any local garages can change these but everybody is unwilling saying it's a black art etc.......
My question is, is it that hard? I mean does it mean they have to crack the whole diff apart and basically rebuild? or is it a case of taking out only bits to press the old bearing out and press in a new one without taking the whole diff apart to a million pieces.

I recently checked the rear subframe has cracked in a few places and I have a new one coming it would be the perfect time to change the bearings on the diff, if it is a relatively simple job. I need to be able to advise the garages.

Cheers

[spd579]

Buy another(used) rear diff. I have like 3

[Scotty@Advanced]

Unless you have the proper know how and tooling to measure the turning torque, preload and backlash of the diff, I would not attempt to change the bearings. You screw it up and you'll roast your differential.

[Monty23]

Do you have an aftermarket poly diff mount? This will cause more diff noise to travel into the cabin. You may be trying to fix something that isn't broken...

[SevenW]

Cheers guys, I mean the bearings themselves are pretty cheap. I know used diffs are cheap, is there anywhere or anybody who reconditions diffs for sale?

The diff mounts are standard.

[MacDaddy]

I rebuilt a differential before, but it was all shims which made it easy.

you need to clean all the gears really well, coat them with Prussian Blue (not too much), observe where the teeth are meshing, use a dial gauge and check all free play, etc.

wasnt hard, but then again it was just shim and torque to spec, I don't know about the audi diff (who even makes it?) but for the ZF differentials they use a crush washers on the input pinion to set end play and you have to set the drag (bascially how many ftlbs need to be applied before the output hub moves).

tossing bearings in there willy-nilly will probably only change the sound of the gear noise but not eliminate it, i would recommend swapping it with a known good used diff.

[SevenW]

I rebuilt a differential before, but it was all shims which made it easy.

you need to clean all the gears really well, coat them with Prussian Blue (not too much), observe where the teeth are meshing, use a dial gauge and check all free play, etc.

wasnt hard, but then again it was just shim and torque to spec, I don't know about the audi diff (who even makes it?) but for the ZF differentials they use a crush washers on the input pinion to set end play and you have to set the drag (bascially how many ftlbs need to be applied before the output hub moves).

tossing bearings in there willy-nilly will probably only change the sound of the gear noise but not eliminate it, i would recommend swapping it with a known good used diff.

Thanks Mac!
I'd love to have a crack at it but, I really don't have the time anymore. I was kinda hoping it would be easy so I could give it to the local garages, but it's looking like I should hunt down a good used item and swap and play.
Well maybe if I get a another unit I can try cracking open my old one. I'm pretty sure the old unit is fine just thought if I could replace the bearings I should.