[Biturbos4] A whine from the rear

[Keman]

I'd really have to hear the sound..

Keep in mind that the rear diff only spins at around 850 rpm on the output 
side and 3300 rpm on the input at 60 mph. When rear diffs go, they make a 
very specific HOWL. Which unfortunately does change with throttle as you 
describe. I've never seen a rear diff go in an audi, and I've replaced the 
seals on them with just half a cup of fluid as all that was left when I 
drained, it, and it STILL was fine.

What's the pitch of the noise? Have you had someone sit in the back to see 
if the noise origination sounds elsewhere?

It never hurts to drain the diff and refill it. See what comes out.

- Keman


On Thu, 13 Jul 2006, Chris Newbold wrote:

> No, no, not from my son in the back seat :)
>
> Just shy of 65k miles, and I'm starting to notice a whine originating
> somewhere in the rear. The whine...
>
>  o is loudest between 65-70MPH
>  o is unaffected by gear: 3rd, 4th, 5th or 6th and the pitch is identical
>  o is unaffected by steering inputs
>  o is strongly correlated to throttle inputs:
>     - it stops if you gently lift and coast
>     - it stops if you dip in and accelerate
>     - it returns in steady cruise
>
> The only things which satisfy all of these observations are:
>
>  o rear differential
>  o center drive shaft bearing (do the B5s even have these?)
>
> I haven't heard of any premature differential failures in the B5 S4, and
> it's not like it's very highly stressed (compared to some other
> comonents). But, hey, there's always a first time.
>
> Anyone have any thoughts or comments?
>
> Keman, I don't know if you're still around, but did you see any such
> failures during your time in the shop?
>
> -Chris
> 2001.5 S4 Avant 6spd
>
>
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