'93 E36 BMW - Differential Carrier Bearing

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Perhaps only two weeks ago, I started noting a 'melodic' sort of whine at speeds from around 60km/h (37mph). I took the vehicle to a mechanic I trust (who I know through a friend) and the verdict, after some investigation, was a carrier bearing in the differential. He suggested I drive it till it sounds properly knackered before getting it rebuilt, as the cost would amount to AU$1000.

For the past 50,000km (31,000 miles) of ownership, I've always noticed a slight whine at highway speeds if you back off the accelerator slightly. The differential fluid was replaced with a good synthetic product of the correct grade/spec for my 320i 2yrs & 25,000km ago. Fluid that was drained did not smell bad, was of a good colour and didn't seem to be full of metal.

I've never heard much talk of differentials in BMWs of this era going bad. So for now, I'm just investigating my options... Would it be better just to source a good, secondhand, low miles unit from a junked vehicle, or would the rebuild be the better option (peace of mind of no failure and that sort of thing)?
 
Go used. It'll be a fraction of the cost and may be better than a rebuilt unit.

That whine you've been hearing is fairly common in an older differential - but you may have started to hear it because you need a new mount.
 
Originally Posted By: B320i
The differential fluid was replaced with a good synthetic product of the correct grade/spec for my 320i 2yrs & 25,000km ago. Fluid that was drained did not smell bad, was of a good colour and didn't seem to be full of metal.

What's viscosity grade in use?
... what grade is called for in the manual ?
I prefer a rebuilt by a reputable guy including oneself.
 
Its a fairly easy diff to set up once its got all its new parts but there are a few special tools needed. I have the BMW set somewhere but haven't done one in many years.
Look for a shop that race preps these, they can do it no problem.
 
Originally Posted By: "zeng"
What's viscosity grade in use?
... what grade is called for in the manual ?

The manual specifies "Your BMW Service Station is familiar with the grades used for servicing." Research I did at the time indicated it was SAF-XO, which is equivalent to 75w-90, and is thus what I used. Cars with an LSD would use SAF-XJ, 75w140. None of the information I have on my car indicates an LSD is fitted, so 75w90 it was.
 
Originally Posted By: B320i
Originally Posted By: "zeng"
What's viscosity grade in use?
... what grade is called for in the manual ?

The manual specifies "Your BMW Service Station is familiar with the grades used for servicing." Research I did at the time indicated it was SAF-XO, which is equivalent to 75w-90, and is thus what I used. Cars with an LSD would use SAF-XJ, 75w140. None of the information I have on my car indicates an LSD is fitted, so 75w90 it was.

Sorry, not trying to burst your air for your choice of 75W90 which is of inadequate viscosity grades, corelates with the whining gear noise phenomenon you encounter presently , IMO.

A 1993 SAE xW90 gear oil were equivalent to today's ISO 150/220 and ISO 320 gear oils with a KV@40*C ranging from 135 cSt to 320 cSt.

However, a current 75W90 typically of KV@40*C 100 cSt or thereabout is thinner at ISO 100 gear oil grades ......
and it doesn't meet OEM requirements then, not saying one can't use 75W90 if you so desire.

A modern day 75W140 of typically KV@40*C 170 cSt would be a safer bet in your E36 differentials.

75W140 @ 4.22




Originally Posted By: B320i
I took the vehicle to a mechanic I trust (who I know through a friend) and the verdict, after some investigation, was a carrier bearing in the differential. He suggested I drive it till it sounds properly knackered before getting it rebuilt, as the cost would amount to AU$1000.

No, don't .
Dump the 75W90 soonest, and replace it with a 75W140 or any ISO 220/320 GL5 gear oils for mitigating whining gear noise turning around the bad situation you're in today.
It's cost is negligible.Just my
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Originally Posted By: "zeng"
Sorry, not trying to burst your air for your choice of 75W90 which is of inadequate viscosity grades, corelates with the whining gear noise phenomenon you encounter presently , IMO.

I have to respectfully disagree (although I appreciate the discussion, don't get me wrong), based on the evidence discussed below, as well as anecdotes from fellow owners. If 75w90 oils were such an issue for these non-LSD examples, it would be widely discussed among E36 owners and enthusiasts, particularly among those who've run their E36s to higher mileages.

A Castrol datasheet I've found just now on the SAF-XO and XJ products doesn't seem to stand with your claims; if this is the factory fluid, or what was used predominantly for a period, how is it the viscosity fits in with the 'modern' figures you quote as being entirely unsuitable?
I searched BITOG, and returned with a link to Castrol (in 2012) stating replacements for the SAF products; note the specific mention against 75w90 of "BMW Approved for used in conventional differentials."
The only evidence I have on 75w140 being recommended was for the LSD-equipped vehicles.

As an aside, the datasheet for the 75w90 indicates a KV40 of 116, and KV100 of 16.1; slightly thicker than the Castrol SAF-XO.
 
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