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      01-11-2020, 10:14 AM   #140
SAMM3Y
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Drives: 2008 m3
Join Date: Feb 2018
Location: NorCal

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Quote:
Originally Posted by Redd View Post
So I pulled the trigger and went full front Powerflex Purple on the diff bushings. I had 3.45 final drive and OS Giken LSD installed at the same time, and already had solid subframe bushings installed. I was also on a lighter break-in 75-140w diff fluid fill when this test was done. Car is a daily-driven DCT with a super loud fully de-catted exhaust. So your mileage may vary.

The bad news - OK, there's definitely diff whine. I can definitely hear it, even over my super load exhaust and radio on. There's a softer high pitch whine (like a supercharger) between 30-40mph. It goes away at 40mph, and is then replaced by a lower pitch - but slightly louder - hum between 70-80mph. Sounds a lot like if you're running noisy semi-slick tires on the road. Not sure if heavier diff oil will help reduce some of the sounds but I doubt it. The whine is actually worse at initial deceleration. You might be cruising along with no noise, lift off, and the decel hum appears. There also seems to be a slight bit more driveline vibration felt in the cabin at certain rpms. Feels a bit like an exhaust pipe vibrating against the car chassis.

The good news - No diff whine above 85mph. Above this speed it sounds/feels like before. This is important as 85+mph is my usual cruising speed. Also, while I can definitely hear the whine, for some reason it doesn't bother me. Maybe cos I'm so used to my car being noisy that I just filter it out automatically. Barely 50kms of driving done and the diff whine has already blended into the cacophony of background noise. Or maybe I'm just going deaf.

So, I don't regret getting the powerflex purple diff bushes but you should seriously reconsider if you are concerned about noise.
I have osg lsd too with purple powerflex on 6mt. It's noisy for sure, even running osg's diff fluid.
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