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      03-17-2020, 07:21 PM   #155
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Quote:
Originally Posted by wyatth View Post
Still thinking about 80a or 95a poly to replace the OE foam mount, but OE rubber in the other 2 spots. I would replace bolts when swapping mounts.
Looking forward to hearing your review on this!
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      03-17-2020, 08:44 PM   #156
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The OE foam mount is 90% solid aluminum with just a think layer of foam around the outside. I am curious whether 80A poly would allow any less movement.
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      03-17-2020, 09:49 PM   #157
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I think itíd be 2 fold, both less initial movement and a single material with longevity. The foam layer seems to break down and that creates the increased movement that leads to broken bolts.
Not sure what Iíll do with the diff. I donít want diff whine on this car.
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      03-18-2020, 07:04 AM   #158
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I drove a convertible with solid aluminum diff and subframe bushings. It whined less noticeably than my sedan with 95A diff and 75D subframe bushings. Probably due to additional sound deadening that convertibles have but possibly due to other body structure changes.
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      03-19-2020, 01:42 AM   #159
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^ That's wild! The idea of solid diff bushings has my ears ringing.
AKG 95A subframe and diff bushings is my only experience (E46M) in this area. I liked the feel, and while the whine was very minor, I'd rather skip that on this car.
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      03-19-2020, 03:46 AM   #160
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Quote:
Originally Posted by pbonsalb View Post
It does not happen to many but it has happened to a few. I run stiffer diff bushings for exactly that reason and put up with a little whine. Mine are AKG black, so 95A. Powerflex purple are 80A, much softer but still slightly harder than rubber.

Which bolt broke? One of the fronts or the rear?
It’s mainly manual where the bolt breaks. The other guy in here that upgraded to purple and doesn’t notice a difference is probably because he’s DCT I don’t think many dct cars have this issue. I’m not an expert but I hear guys with super chargers also have this problem with either transmission.
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      03-19-2020, 07:00 AM   #161
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Is it one of the two front bolts that breaks or the single rear bolt?

I recall reading of people with 80A purple diff bushings complaining about whine. Driving style can play a roll. The rpm at which whine occurs is in a limited rpm range, which of course varies by gear. You will likely only notice it in the upper gears when traveling at a steady speed in the particular rpm range. Some people may drive in such a way that that they tend to avoid the rpm range or pass through it quickly. That is not the case for me. I notice it in 6th of my 6MT when cruising on the highway probably in the 55-70 mph range. I changed my bushings years ago and donít really pay attention to the whine anymore, but if I did, I could pick a narrower speed range at which I hear it most; my recollection of 55-70 covers onset speed through tapering off speed.
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      03-19-2020, 12:22 PM   #162
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Quote:
Originally Posted by North.E92 View Post
Itís mainly manual where the bolt breaks. The other guy in here that upgraded to purple and doesnít notice a difference is probably because heís DCT I donít think many dct cars have this issue. Iím not an expert but I hear guys with super chargers also have this problem with either transmission.
I wonder if it's from aggressive driving, dumping clutch on shifts and the extra driveline vibration causes the bolt to break over time. I have a friend that broke it twice, he shifts hard. My bro has been autocrossing my car and I notice he shifts hard af... I can't imagine it being good for that.
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      10-26-2020, 07:43 PM   #163
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10,000 mile update!
Well, as everyone knows on the street the solid subframe bushing have no downside. And, in fact, in my street driving I can't tell one whit of difference either positive or negative. I think the "the rear feels more planted" on the street is placebo effect.

However, I can absolutely confirm one place where it absolutely makes a difference. Ran VIR last fall and didn't really think about it until I ran VIR again just this past weekend. Those of you who know the track know that at the start-finish line the pavement is uneven and when you come down the front straight with a big head of steam and under full-throttle deep into 4th gear the stock rear end squirms around a bit. I've had driver's I've been running with tell me, "your rear is squirming and dancing around quite a bit," at that point in the track.

For some reason it was only evident to me after another driver noted how his rear end is not "planted" in the exact same section, this past weekend. Then I realized that the rear subframe bushings made a big difference right there. When your car is rock solid and not squirming around you don't think about what it used to be like, you just motor right long and life is good. So, objectively that's one spot and one situation where there's absolutely no question the solid subframe bushings are really doing what they're supposed to. This is a high-speed, moderate load situation and that's where the effectiveness of this mod really shows.
No change in my opinion on the diff bushings, you can see my other posts.
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      10-26-2020, 11:20 PM   #164
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Quote:
Originally Posted by VictorH View Post
10,000 mile update!
Well, as everyone knows on the street the solid subframe bushing have no downside. And, in fact, in my street driving I can't tell one whit of difference either positive or negative. I think the "the rear feels more planted" on the street is placebo effect.

However, I can absolutely confirm one place where it absolutely makes a difference. Ran VIR last fall and didn't really think about it until I ran VIR again just this past weekend. Those of you who know the track know that at the start-finish line the pavement is uneven and when you come down the front straight with a big head of steam and under full-throttle deep into 4th gear the stock rear end squirms around a bit. I've had driver's I've been running with tell me, "your rear is squirming and dancing around quite a bit," at that point in the track.

For some reason it was only evident to me after another driver noted how his rear end is not "planted" in the exact same section, this past weekend. Then I realized that the rear subframe bushings made a big difference right there. When your car is rock solid and not squirming around you don't think about what it used to be like, you just motor right long and life is good. So, objectively that's one spot and one situation where there's absolutely no question the solid subframe bushings are really doing what they're supposed to. This is a high-speed, moderate load situation and that's where the effectiveness of this mod really shows.
No change in my opinion on the diff bushings, you can see my other posts.
I've seen a 335i with stock subframe bushings (softer than M3 but still rubber) do a side-to-side wiggle with its rear end while at normal street speeds (60-70kph?) going over a relatively smooth bridge joint. It shocked me how much movement there was, I would say at least an inch of sideways displacement cos I could see it with my naked eye while driving behind the 335i. And it took like 2-3 cycles to settle. I've felt the same movement under the same conditions before in my M3 but seeing it move that much was a bit of a shock. My car now has solid subframe bushes - zero wiggle and as you have said, zero NVH on street.
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      10-26-2020, 11:27 PM   #165
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The difference with solid sfb was extremely noticeable on my first 1st-2nd gear wot on the bumpy/wavey Seattle streets. I've been told I have a hyper sensitive tush since my very first track day though, so everyone's experience will differ. I wasn't really expecting anything more than a reduction in wheel hop.
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