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      08-11-2018, 09:49 AM   #1
Phil_M_Robinson
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E92 M3 Differential Bushings

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Hi all,

As part of my rear axle refresh I am going to change the bushings in the differential. There is just too much deflection under load.

Before I ask the question, I will say that my car sees track and road use. I have BW GroupN engine mounts and am going to put solid subframe mounts in, as well as SPL Components arms, with Rogue Spindle Bushings - I can deal with NVH.

So in terms of material choice for the differential:

I am looking at either Delrin or Aluminium mounts, or a mixture of the two (Delrin for the rear mount/Aluminium for front mounts)

Therefore, does Delrin reduce noise considerably over Aluminium? Or is the difference so small that the trade off in NVH is worth the extra performance?

And if Delrin reduces noise considerably over Aluminium, how great is the gap in performance?

Hope that makes sense!

And many thanks in advance for your replies

Phil R
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      08-11-2018, 10:11 AM   #2
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The group n motor mounts donít add much nvh. If you said you had harder trans mounts and did not mind them, then we would know you have some tolerance for nvh. Iíd say go delrin on the diff if you street drive the car and donít think you would mind nvh. I would not go harder on a street car. I drove a delrin diff E93 and it was not objectionable at all but the top was down. My car has 95A poly and it is as much nvh as I would want in my comfy cruiser street car. I have an E36 with solid front and 75D poly diff mounts and it is more nvh than I want in a street car.

For the subframe, solid is fine by most accounts. I run 75D in the subframe, which is close to delrin but my car is a street car.
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      08-11-2018, 10:28 AM   #3
Phil_M_Robinson
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Fantastic info there - thank you. Delrin it is!
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      08-11-2018, 01:28 PM   #4
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My head is ringing just reading this.
I suspect seriously diminishing returns with deflection with stiffer materials. Iíd do Powerflex Purple even if you can handle NVH. I believe someone with experience said they were 90% of the benefit/feel of solids, with 20% of the whine.
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      08-11-2018, 03:17 PM   #5
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I donít think the diff mounts are a problem on these cars and stiffer bushings there wonít make as much improvement as in the subframe. I changed only because a few cars have broken mounts, bent subframes and broken diff covers. Very few cars, but I thought I might drag race mine in drag radials and changed them while I was in there.
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      08-11-2018, 03:53 PM   #6
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I did solid subs and purple diff bushings. At about 55mph is is super loud. Almost where the radio won’t drown it out. Change it a bit up or down in the rpm and it’s fine.
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      08-11-2018, 05:08 PM   #7
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I did Alekshop subframe and diff bushings, there is a whine but no V or H IMO. I believe they were delrin/aluminum bushings. I've upgraded every thing except for my transmission mounts. I'm not so sensitive to NVH but all that I've read is that they are unbearable.

But no complaints by any means on my Alekshop subframe and diff bushings.
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      08-11-2018, 11:40 PM   #8
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i did everything at once, sway bars, solid subframe, purple diff, monoball FCAB, and the only noise i have noticed is a diff whine above 80 km/h up to around 100 km/h, outside that range i hear absolutely nothing. the whine is noticeable even with radio and akra evo, but i enjoy the whine it sounds like supercharger whine, but i also wonder if i could've handled delrim diff mounts. however, accrording to Hujan from another thread, he thought delrin diff mounts were unbearable so he switched back to purple diff
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      08-12-2018, 07:32 AM   #9
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Purples are 80A. Next step up is 95A, which I have, then 75D, then delrin, then solid. I get the whining or singing at around 60 mph in 6th. You notice it most if you are forced to stay in that range which spans about 10 mph. If you can pass through it, then you donít notice much. If you had a commute that kept you in it, the singing would get old.

I tried stiffer trans mounts and they are much more objectionable.
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      08-14-2018, 05:29 PM   #10
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Many thanks to everyone who replied.

I have purchased some Powerflex Purple Diff mounts to go with the Solid Subframe Mounts.
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      08-14-2018, 06:18 PM   #11
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***EDITED***

Diff mounts will cause NVH problems, subframe mounts will not.

BMW even moved up to solid subframe mounts for the F8X.
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Last edited by dparm; 08-14-2018 at 09:53 PM..
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      08-14-2018, 06:31 PM   #12
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Quote:
Originally Posted by dparm View Post
There's been a litany of discussions on this and my understanding is that the subframe mounts contribute much more to NVH than differential mounts. In fact, I thought that BMW went with solid subframe mounts on the F8X?
Other way around. Virtually no NVH with solid subframe mounting. Diff whine occurs with harder durometer diff bushings.
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      08-14-2018, 06:59 PM   #13
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Quote:
Originally Posted by dparm View Post
There's been a litany of discussions on this and my understanding is that the subframe mounts contribute much more to NVH than differential mounts. In fact, I thought that BMW went with solid subframe mounts on the F8X?
Below ...

Quote:
Originally Posted by Phil_M_Robinson View Post
Other way around. Virtually no NVH with solid subframe mounting. Diff whine occurs with harder durometer diff bushings.
That's my understanding as well after reading every thread/post that has the word "subframe" in it. Though my only experience with swapping either mount is with AKG 95A (in both places) on my previous E46. NVH was non-existent, but diff whine was detectable (albeit very mild with 95A).
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      08-14-2018, 08:06 PM   #14
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Quote:
Originally Posted by pbonsalb View Post
Purples are 80A. Next step up is 95A, which I have, then 75D, then delrin, then solid. I get the whining or singing at around 60 mph in 6th. You notice it most if you are forced to stay in that range which spans about 10 mph. If you can pass through it, then you donít notice much. If you had a commute that kept you in it, the singing would get old.

I tried stiffer trans mounts and they are much more objectionable.
I'm taking the rear diff for Giken LSD and wondering if I should upgrade my diff bushings also. Do the Purple 80A add any NVH? Car is daily driven with 3-4 trackdays a year.
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      08-14-2018, 09:00 PM   #15
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From what I have read, purple still add some whine, but should add the least whine of the aftermarket options. I did not try the purple, just the 95A black, so I don't have any actual experience. I have used purple subframe and rtab bushings on my E36M3 before and they are pretty squishy compared to black, but a slight step up from new stock and probably a noticeable step up from 5-10 year old stock.

Supposedly there is some sort of damper you can add that may reduce while. I do not know the details. Malek mentioned it once. Might be from an M1 or 135i. I do have some recollection of some E36 having a little add on box that screwed into a boss on the subframe and supposedly had a damping effect. Maybe this part that could work on the E9xM3 subframe is something like that. Does anyone have more info?
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      08-14-2018, 09:54 PM   #16
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Quote:
Originally Posted by Phil_M_Robinson View Post
Other way around. Virtually no NVH with solid subframe mounting. Diff whine occurs with harder durometer diff bushings.
Thanks, I edited my post.
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      08-15-2018, 12:16 AM   #17
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Quote:
Originally Posted by pbonsalb View Post
From what I have read, purple still add some whine, but should add the least whine of the aftermarket options. I did not try the purple, just the 95A black, so I don't have any actual experience. I have used purple subframe and rtab bushings on my E36M3 before and they are pretty squishy compared to black, but a slight step up from new stock and probably a noticeable step up from 5-10 year old stock.

Supposedly there is some sort of damper you can add that may reduce while. I do not know the details. Malek mentioned it once. Might be from an M1 or 135i. I do have some recollection of some E36 having a little add on box that screwed into a boss on the subframe and supposedly had a damping effect. Maybe this part that could work on the E9xM3 subframe is something like that. Does anyone have more info?
i had asked malek before and he said the differential damper doesn't do much after trying it on a couple cars. He also recommended Powerflex Poly diff bushings if car is DCT and primarily a street given car. When asked about purple vs black, he recommended purple because he thought if you do black, might as well go Delrin at that point.
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      06-20-2022, 02:51 PM   #18
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Quote:
Originally Posted by Phil_M_Robinson View Post
Many thanks to everyone who replied.

I have purchased some Powerflex Purple Diff mounts to go with the Solid Subframe Mounts.
My apologies for reviving a super old thread mate, but what were your impressions with solid subframe mounts and 80A diff mounts?

Much Thanks!
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