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      03-19-2015, 10:59 AM   #23
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Anybody have any feedback on how degraded the old diff bushings are after a certain number of miles as opposed to new OEM stuff? Curious how these look when they come out.
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      03-19-2015, 11:35 AM   #24
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Quote:
Originally Posted by kitw View Post
I found the whine of Delrin diff bushings to be intolerable. The subframe bushings made a huge difference and trivial NVH by themselves. I would do the subframe bushings first - you can always go back and do diff bushings later (they don't require dropping the subframe to do)

To me, the noise was barely discernible, and after an exhaust, I can't hear it at all. So my advice to those worried about the whine is to cure that w/an exhaust
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      03-19-2015, 01:53 PM   #25
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A bimmerforums member replaced the diff bushings with AKG red poly and reports quite a lot of gear noise.

http://www.bimmerforums.com/forum/sh...2#post28388342
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      03-19-2015, 04:41 PM   #26
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Quote:
Originally Posted by pbonsalb View Post
A bimmerforums member replaced the diff bushings with AKG red poly and reports quite a lot of gear noise.

http://www.bimmerforums.com/forum/sh...2#post28388342
Yeah I've read these are basically solid as far as nvh is concerned. The akg blacks are more akin to a group N rubber so that should offer at least a little compliance.
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      03-19-2015, 09:21 PM   #27
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I use akg red on my e36 m3 and have no complaints, but it has Powerflex purple subframe bushings. I think one of the two locations should be softer than the other for a street car. I still have not done my e90 m3 so I am following these threads.
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      03-23-2015, 02:49 PM   #28
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Quote:
Originally Posted by Shredicus View Post
Yeah I've read these are basically solid as far as nvh is concerned. The akg blacks are more akin to a group N rubber so that should offer at least a little compliance.
Did you ever get your set installed brother? I'm waiting to pull the trigger on these but awaiting on your feedback.
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      03-23-2015, 03:14 PM   #29
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Originally Posted by WickedE93 View Post
Did you ever get your set installed brother? I'm waiting to pull the trigger on these but awaiting on your feedback.
Not yet my man. Had a few setbacks but I'm looking to get the work done at EAS in the next month or so. I'll definitely follow up with impressions once I've got them in.
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      03-23-2015, 03:29 PM   #30
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Quote:
Originally Posted by Shredicus View Post
Not yet my man. Had a few setbacks but I'm looking to get the work done at EAS in the next month or so. I'll definitely follow up with impressions once I've got them in.
Nice! sounds good brother I might actually beat you to the install if things go well I can post a review for you lol.
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      03-25-2015, 11:51 AM   #31
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I am getting ready to buy as well. I think I will go with AKG 95A for the subframe bushings and harder AKG 75D for the diff bushings. 75D in both places is going to transmit vibration and the car is supposed to be a comfortable driver. I have a 600+ rwhp turbo E36M3 as my toy. Any thoughts on bushing durometer and which durometer to put where?
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      03-25-2015, 04:55 PM   #32
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Quote:
Originally Posted by pbonsalb View Post
I am getting ready to buy as well. I think I will go with AKG 95A for the subframe bushings and harder AKG 75D for the diff bushings. 75D in both places is going to transmit vibration and the car is supposed to be a comfortable driver. I have a 600+ rwhp turbo E36M3 as my toy. Any thoughts on bushing durometer and which durometer to put where?
You said "vibration" but I assume you mean noise. I've noticed no increase in vibration or harshness from solid aluminum subframe bushings combined with delrin/aluminum differential bushings.

I can't say for sure because I did both sets of bushings at the same time, but I would be very confident in saying that if you did solid aluminum subframe bushings with nothing else, you would notice absolute no ill effects (vibration, harshness, or noise) and that changing the differential bushings at that point would only affect noise, with the harder substances leading to greater levels of diff whine and drivetrain knocks.

I cannot imagine going with polyurethane for the subframe, street car or otherwise. Unlike solid aluminum, polyurethane is not a service-free item and will need to be periodically lubed if not replaced all together. That would be a major PITA in the subframe application. The differential is a bit more understandable since the bushings there are much more easily replaced.

I strongly suspect that solid subframe bushings combined with a relatively mild durometer polyurethane for differential bushings would yield most of the benefits of solid bushings in both locations, with a fraction of the noise penalty. But I cannot confirm first hand, of course. At least not yet.
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      03-25-2015, 05:10 PM   #33
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If you read the reports from those who have done the delrin or solid bushings, they all mention noise. A few even removed the stiff diff bushings. Have to find an acceptable balance. I agree you might be able to go solid or near solid in one of the 2 locations and still have a comfortable driver, but not both locations.
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      03-25-2015, 05:34 PM   #34
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Quote:
Originally Posted by pbonsalb View Post
If you read the reports from those who have done the delrin or solid bushings, they all mention noise. A few even removed the stiff diff bushings. Have to find an acceptable balance. I agree you might be able to go solid or near solid in one of the 2 locations and still have a comfortable driver, but not both locations.
I haven't seen a single report of increased noise from someone who went solid on the subframe but left the differential stock. And mostly the point of my last post was that vibration is not a part of the equation, even if you go with solid bushings in both locations. Noise yes, vibration no.
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      03-25-2015, 10:16 PM   #35
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I don't have any problem with the subframe. My concern is more the diff failure that a few have experienced - I'd like to be able to run the car at the strip and not worry. I just figured I would upgrade the subframe bushings at the same time even though they do not seem to be a problem. Problem seems to be diff moving in subframe.
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      03-26-2015, 10:40 PM   #36
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Quote:
Originally Posted by pbonsalb View Post
I don't have any problem with the subframe. My concern is more the diff failure that a few have experienced - I'd like to be able to run the car at the strip and not worry. I just figured I would upgrade the subframe bushings at the same time even though they do not seem to be a problem. Problem seems to be diff moving in subframe.
First, while I think you're right that the diff bolt is much more likely to fail than the subframe, a subframe failure would be far more difficult to repair. You're right that of failure is an important consideration; but so, too, is the severity of harm when it does occur.

Second, I'm by no means an expert, but its my understanding that laxity in the subframe is what amplifies the forces at the differential bolt. I think of it like a whip: Sure, the tip is moving with the most speed and force, but that force and speed has its origins in movement at the handle. In this analogy, the diff bolt is the tip of the whip, while the subframe is the handle. It's my belief that the more deflection you prevent at the subframe, the less there will be at the differential.

But this is all general theory and discussion. You have to do what's best for you and your car at the end of the day. Whatever you decide to go with, I'm sure it will be far better than the OEM bushings and will hopefully serve you and your car well for many healthy miles!
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      03-31-2015, 08:29 AM   #37
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There is presently another useful thread on the subject in another subforum so I will link it here:

http://www.m3post.com/forums/showthread.php?t=1109089

I am still on the fence as to which way to go. I have no interest in vibration or whine that makes me dislike driving the car. I am not a 25 year old kid and this is not my occasionally driven track car. Opinions seem to be all over the place.
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      03-31-2015, 12:57 PM   #38
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Quote:
Originally Posted by pbonsalb View Post
There is presently another useful thread on the subject in another subforum so I will link it here:

http://www.m3post.com/forums/showthread.php?t=1109089

I am still on the fence as to which way to go. I have no interest in vibration or whine that makes me dislike driving the car. I am not a 25 year old kid and this is not my occasionally driven track car. Opinions seem to be all over the place.
I'm in the same boat as you. I'm personally thinking of going with the regular Powerflex "street" poly diff bushings. I think these are probably the softest poly available yet hopefully a worthy step up from the factory rubber pieces to stop the diff from bouncing around.
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