low speed turns making noise (resolution: new diff / differential fluid)

Hi guys,

to update on the issue I had my service technician replace my diff oil - he agreed this would be the cause of the issue but noted it may take 1,500kms to fully wear in. It has definately mitigated the issue almost completely, but a little noise still remains from time to time. Has definately helped.

We're not talking about a 'grinding' noise as described in the 'grind' of a transmission, right?

I describe the noise more like a long continuous metal-on-metal friction sound, almost like the sound a train makes while stopping on rails, just not as high-pitched.


I get this when turning tightly (mostly right turns), and only on occasion. I self-correct the noise by turning in a little - never tried to depress the clutch though.

Anyone know if this is the same issue?

Ahhhh!
So it's diff fluid causing this grinding sound from the rear end that has been bothering folks with this car for years.
It's awesome that someone finally figured this out. I hope in the future that people search the forum when this happens to them. They will be able to find this very helpful thread that obviously no one had ever thought to post before.

funny, i just brought my car in for this on saturday.

CorrectoMan wrote

We're not talking about a 'grinding' noise as described in the 'grind' of a transmission, right?

I describe the noise more like a long continuous metal-on-metal friction sound, almost like the sound a train makes while stopping on rails, just not as high-pitched.


I get this when turning tightly (mostly right turns), and only on occasion. I self-correct the noise by turning in a little - never tried to depress the clutch though.

Anyone know if this is the same issue?

Sounds like wheels scrubbing on guards or riding with a flat.

At 4K on E90 2011, after they services the diff fluid, I started to hear the grinding noise at low speed turing right. They added the diff fluid and still was there. They replaced the diff and all is well.

Yea also in my e92 as soon as I reverse or get out of my drive way it makes a loud cranking noise coming from what sounds like the left side of the car ... No clue what it is

Anyone have this part# for Canada? Apparently it's different.
Thanks

Hmmm of course there is the alternate solution which is to leave it as it is...its a high performance diff which can make some noise...especially when cold and on tight turns.
Adding extra slip agent to a system which requires a high level of friction in order to function as designed is to some folk a bit of a mistake.

Dellort_M3 wrote

Anyone have this part# for Canada? Apparently it's different.
Thanks

The part number I listed on Page 1 is correct for Canada.

I had no issues requesting this at my dealership in Montreal. It is even listed on the work order.

///Montreal3 wrote

The part number I listed on Page 1 is correct for Canada.

I had no issues requesting this at my dealership in Montreal. It is even listed on the work order.

Thanks
I tried to ask my dealership about this part and they couldnt find anything.
I also found this document from 2010.

SenorFunkyPants wrote

Hmmm of course there is the alternate solution which is to leave it as it is...its a high performance diff which can make some noise...especially when cold and on tight turns.
Adding extra slip agent to a system which requires a high level of friction in order to function as designed is to some folk a bit of a mistake.

Anyone care to go into more depth on this statement? I was thinking about having the new diff fluid put in, but if the positive is only noise reduction and the negative is something more problematic, I might leave it alone.

One of the std OEM diff fills is Castrol SAF-XJ. The Noise reduction fill is Castrol SAF-XJ to which BMW has added extra slip agent. This fill is only given to customers who complain about diff noise. The question you have to ask yourself is why BMW don't make the OEM fill the Castrol with extra slip agent if there was no detrimental effect? (The cost of the extra slip agent is pennies.)

SenorFunkyPants wrote

Hmmm of course there is the alternate solution which is to leave it as it is...its a high performance diff which can make some noise...especially when cold and on tight turns.
Adding extra slip agent to a system which requires a high level of friction in order to function as designed is to some folk a bit of a mistake.

SFP sounds more informed than me, but his argument seems perfectly sound. In engineering, there are always trade offs. Nothing is the strongest AND lightest possible design. You want to get rid of a noise caused by excess friction in non performance driving situation, you may sacrifice some of the effectiveness of you diff in performance situations.

I'm pretty sure my noise is all but gone. Then again, with my new exhaust how am i supposed to hear it?

jdemetry wrote

SFP sounds more informed than me, but his argument seems perfectly sound. In engineering, there are always trade offs. Nothing is the strongest AND lightest possible design. You want to get rid of a noise caused by excess friction in non performance driving situation, you may sacrifice some of the effectiveness of you diff in performance situations.

Mechanically, I don't know if it's correct. The fact that it's noisier doesn't mean that it's working better or worse.

If we assume he's correct, I go with the additive. For me, there is no kind of driving that I do that I need some incremental level of performance as a tradeoff for noise.

I could get a locker for my F-150 too, but the noise and feel for what is mostly highway driving is not worth the tradeoff.

Fair enough, its your car and your choice....I choose not to have the extra slip oil.
Just so everyone is clear as to what is happening:

"The Variable M Differential Lock recognizes the differential speed building between the driven wheels and generates pressure in an integrated shear pump. This pressure activates a multiple plate clutch via a piston, and conveys drive forces to the wheel with better grip, according to the difference in wheel rotation speed. In extreme cases, the entire drive forces may be transmitted to the wheel with a better frictional coefficient."

The rubbing groaning noise you hear usually with cold diff oil and in tight turns is the noise made by the steel clutch plates held together in a pack slipping against each other. These high friction clutch plates have to be able to transmit some 350bhp without slipping to one wheel at one extreme and yet slip relatively freely when unloaded to allow the car to make a turn.
The question is, does adding an extra slip agent to the oil to enable the clutch plates to slip easier and thus quieter in a unloaded turn effect its function at the other extreme.
All I know is my car makes a little noise in tight turns when cold but locks fully when needed - I'm not going to risk that by adding a non OEM oil.

SenorFunkyPants wrote

Fair enough, its your car and your choice....I choose not to have the extra slip oil.
Just so everyone is clear as to what is happening:

"The Variable M Differential Lock recognizes the differential speed building between the driven wheels and generates pressure in an integrated shear pump. This pressure activates a multiple plate clutch via a piston, and conveys drive forces to the wheel with better grip, according to the difference in wheel rotation speed. In extreme cases, the entire drive forces may be transmitted to the wheel with a better frictional coefficient."

The rubbing groaning noise you hear usually with cold diff oil and in tight turns is the noise made by the steel clutch plates held together in a pack slipping against each other. These high friction clutch plates have to be able to transmit some 350bhp without slipping to one wheel at one extreme and yet slip relatively freely when unloaded to allow the car to make a turn.
The question is, does adding an extra slip agent to the oil to enable the clutch plates to slip easier and thus quieter in a unloaded turn effect its function at the other extreme.
All I know is my car makes a little noise in tight turns when cold but locks fully when needed - I'm not going to risk that by adding a non OEM oil.

Thanks again for the in-depth explanation. Makes me feel a lot better to know that if I don't get the fluid changed, I'm not doing any damage to the system. Sounds like it's a fix for "customer satisfaction", and nothing more.

serranot wrote

Mechanically, I don't know if it's correct. The fact that it's noisier doesn't mean that it's working better or worse.

If we assume he's correct, I go with the additive. For me, there is no kind of driving that I do that I need some incremental level of performance as a tradeoff for noise.

I could get a locker for my F-150 too, but the noise and feel for what is mostly highway driving is not worth the tradeoff.

The way I understand SFP's comments, and LSD's in general, I think it's likely that reducing friction between the friction plates in the LSD likely reduces it's effectiveness. Perhaps not in a meaninful/observable way. It's all relative, how much functionality of the LSD would you trade for a noise free diff? (rhetorical question)