RE: E30 Bearing roar in the back.

["Fadeev, Alex" <Alex.Fadeev@xxxxxxxxxxxxxx>]

> There is an obvious bearing roar in the back of my 325iX.

	Could be a wheel bearing going bad (you should have around 120K
miles on your car). Or it could be that increased tolerance (through wear)
in the rear differential are showing through as low frequency hum. Both
would increase with speed. 
	You should replace the bearing (~$200) if that what it turns out to
be. 
	Rear differentials (LSD's in particular) all start humming in
6-digit mileage range. "They all do it". You can marginally quiet the hum
with higher wiscosity rear differential oil, but it will still be there.
What's more important, your LSD will continue to hum happily for at least
another 50K miles before it really needs attention. 
	Have a qualified mechanic identify what the problem really is.

> I took a 
> mechanic of some local repute for a test ride and he said "carrier 
> bearing in the differential" and proceeded to tell me that bearing 
> replacement is a waste of time.  He said to replace the diff (to the 
> tune of a cool 1000.00) and move on.  

	If it is indeed the differential, $1K sounds a bit excessive for
replacement unless you are buying all new parts.
     
> My questions: Can you tell just riding in the car?  

	If it's one of the front bearings, the noise should go away on
right/left turns (bad left/right front bearing). 
	Rear wheel bearings are a bit trickier to identify and differentiate
from the differential hum. 
	If the bearing is really gone, you should be able to move the wheel
in and out a bit. But that is more of a 'my wheel is about to fall off'
test.

> Isn't a wheel bearing problem more likely?

	Yes!
	What's your mileage?

> Are wheel bearings a problem with the iX's?
  
	All E30 bearings get replaced between 100-160K miles. 
	This is something to keep in mind when shopping for a used E30 in
that milage range - how many new wheel bearings does it have? At $200/per
bearing, you are looking at $800 outlay. This is really not a DIY job since
you need a $300+ in tools alone to do it.

good luck,
alex

'89 325i  140K with 2 new wheel bearings
'90 325is 100K with 0 new wheel bearings

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