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I was told to use BMW OEM by at least 3 local indy shops...apparently there could be noise coming out if using a different fluid in the long run (and especially if track/drive hard)

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Im getting ready to flush my rear diff I was just wondering if I should go with OEM fluid or Castrol syntax 75w140

If I'm not mistaken Castrol Syntrax + friction modifier is what you get in the BMW bottle. So you can use the Castrol Syntrax for LSDs but you will need to add the friction modifier to it so that you don't get the grinding noise.

Make sure you make some sharp and slow figure 8s in an empty lot so get the oil between the clutches.
 

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If I'm not mistaken Castrol Syntrax + friction modifier is what you get in the BMW bottle. So you can use the Castrol Syntrax for LSDs but you will need to add the friction modifier to it so that you don't get the grinding noise.

Make sure you make some sharp and slow figure 8s in an empty lot so get the oil between the clutches.
I put bmw oem diff fluid in and i get the odd grind here and there. Is the Friction Modifier already added by the manufacturer of the oem bmw diff fluid? or is this something you have to buy separately and add yourself??
 

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What's the part number of the bmw fluid you used? There is a unique PN for M differentials. Maybe you got the 'regular' bmw diff oil?
 

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I put bmw oem diff fluid in and i get the odd grind here and there. Is the Friction Modifier already added by the manufacturer of the oem bmw diff fluid? or is this something you have to buy separately and add yourself??

If you bought the bottle that said "axle fluid + FM booster", then it had the friction modifier added already. The diff fluids for M cars should have the friction modifier added already.

I would suggest you find an open and safe lot and do some slow, tight figure 8 turns. I usually do a minimum of 10. That should fix the occasional grind.
 

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I was told to use BMW OEM by at least 3 local indy shops...apparently there could be noise coming out if using a different fluid in the long run (and especially if track/drive hard)

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That's odd to me. I have had two , including the one I have now, the three independent BMW shops I have used [one in Yakima wa, one in Issaquah wa and one in Bellevue wa] have all recommended Red Line for the Diff, smg, and for years I have used nothing but Red Line 10w60 in the V10.
 

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That's odd to me. I have had two , including the one I have now, the three independent BMW shops I have used [one in Yakima wa, one in Issaquah wa and one in Bellevue wa] have all recommended Red Line for the Diff, smg, and for years I have used nothing but Red Line 10w60 in the V10.
The Indy I went to didnt mention Red Line, I will have to check that out next time....is it less cost than the BMW?

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The Indy I went to didnt mention Red Line, I will have to check that out next time....is it less cost than the BMW?

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Yes, much less. Go to Red Line oil and put in all your car info, it tells you what to use. You can buy [I believe] straight from them, Ebay, numerous M car suppliers. Again, for 7 years, and two E60 M5's, it all I have ever used in the engine, SMG and the diff [75w140 part #57914]..the diff oil has the limited slip additive, takes a bit less than 2qts, the 10w60 with extra zddp, check Ebay, there is an M racing company out of Illinois that will sell you 4 gallons for about $196, shipped free..I have been at this awhile
 

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I’m using Redline ShockProof Lightweight 75w140
 

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What's the part number of the bmw fluid you used? There is a unique PN for M differentials. Maybe you got the 'regular' bmw diff oil?
I don't have the part # now... it's been a while so I would have to dig thru my receipts.

I will try the figure 8 thing next season - car is off road now, i'll be doing the throttle gears and smg PLCD sensor this winter.
 

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Yes but you don't have a stock differential :)

I'm almost sure the regular bmw fluid has friction modifier, but the M fluid has an extra dose. As much as I use redline I chose the M fluid for the diff.
Do you have an exact part number for that M fluid? I'm getting a little confused with the multiple hits. Thanks..
 

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Try this:

 
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