Quote:
Originally Posted by pbonsalb
I never had any noise, but when I changed my fluids around 60k when I did the rod bearings, I used the FM fluid and continue to have no noise. Sometimes I wonder whether lockup might be improved with non FM fluid. I can light up the rear tires pretty easily and have been running 285/35/18 PSS and now 295/30/18 EC Sport. I have all the bolt on mods and tune and probably make close to 400 rwhp, about 15% over stock.
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Your car sounds awesome

Do you track it? ... Yeah, some people tell me that lockup is potentially decreased with the FM fluid, which would be more of a concern for racing/tracking your car instead of just normal driving conditions. But, the majority of "experts" (certified BMW mechanics mostly) I have asked say that diff performance with FM fluid is not impacted to the point that it necessarily matters..? And, I told all of them that I will be taking my car to the track about once a month. You know, you ask 3 "experts" one question and you get three different answers lol.
I changed out my diff fluid yesterday while my car was on a lift for an exhaust mod, and one benefit of doing that was that we were able to observe the fluid as it came out. It definitely had a pronounced silvery hue to it, so there are metal bits in it, which does not make me super happy! And it was changed not too long ago- 15,000 miles. I put the FM booster fluid in and I have noticed a reduction in clunking noises from my diff, but they have not gone away completely. I am just going to keep paying attention to it.