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

[audioMeth]

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

[Totti]

Originally Posted by CorrectoMan

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.

[vb_man]

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.

[M3Bes]

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

[Dellort_M3]

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

[SenorFunkyPants]

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.

[///Montreal3]

Originally Posted by Dellort_M3

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.

[Dellort_M3]

Originally Posted by ///Montreal3

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.

[davesaddiction]

Originally Posted by SenorFunkyPants

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.

[SenorFunkyPants]

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.)

[MKE_M3]

Originally Posted by SenorFunkyPants

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.

[Totti]

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

[serranot]

Originally Posted by jdemetry

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.

[SenorFunkyPants]

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.

[davesaddiction]

Originally Posted by SenorFunkyPants

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.

[MKE_M3]

Originally Posted by serranot

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)

[fastmike]

Just got the BMW Diff fluid changed in my car @ EAS, diff is quiet now. The whhhrrr-whhhrrr-whhhrrr noise was getting irritating on my car. 70k miles on the odo.

[TX]

37K miles and have loud diff whomp whomp whomp noise turning at slow speeds around tight corners, right is worse than left. It actually starts jerking the car at times when it grabs. Is there a diff lube replacement cycle around this mileage that I need to do or a topping off schedule? Any DIYs?
thanks.

[jphughan]

I specifically asked for the non-FM version when I got my fluid changed at 26K. The FM version is a BMW modification from Castrol's formula and intended solely to quiet the diff, which combined with the fact that it's not listed for use outside the US makes me wonder if BMW created this variant just to appease whiny Americans and potentially achieved quieter operation at the cost of performance. I definitely have diff noise when cold and turning corners at low speeds, but seeing as I enjoy my car at the track, I'll take that over reduced performance without hesitation.

UPDATE: Yep, turns out that friction modifiers decrease noise by decreasing performance. New post later in this thread: http://www.m3post.com/forums/showpos...2&postcount=63.

[Vic311]

Originally Posted by TX

37K miles and have loud diff whomp whomp whomp noise turning at slow speeds around tight corners, right is worse than left. It actually starts jerking the car at times when it grabs. Is there a diff lube replacement cycle around this mileage that I need to do or a topping off schedule? Any DIYs?
thanks.

Change the fluid, immediately.

http://www.m3post.com/forums/showthread.php?t=714350

[SenorFunkyPants]

For info my car's diff made the cold oil, low speed groan on turns since I bought it with 3k miles and I have resisted having the diff oil with extra friction modifier added.
Now 5 years later and at 50k miles it still makes exactly the same noise and still fully locks up when required.

[kaotik182]

Is there an issue going back to regular/ non-FM fluid? At 1200 mile service, dealer put in the regular/ non-FM fluid. At 30k mile service, the same dealer put in the fm fluid, but I never had an issue with noise. I did not know they put the fm fluid until the work was done and I saw the work invoice. I told them about it after but it was too late. They said it is the only fluid they carried/ dealer excuse. I will be doing my 60k mile service soon. Thanks in advance for the response.

I asked this same question in the DIY: Differential Fluid Change thread in the DIY section almost a week ago with no response. Link below. I'm hoping more foot traffic in the general section will give me a response.

http://www.m3post.com/forums/showthr...=714350&page=3