Help me choose Differential Bushings

[dcaron9999]

Hi there.

Im swapping my stock 3.08 final drive open Diff to a 3.46 Quaife LSD, on my 6-speed manual 135i (M sport package). My 135i sees the track regularly but is not a dedicated track car. With the new final drive, endurance brake pads, and stiffer rear toe arms, there will be increased loads on the three diff carrier bushings.

"While Im in there", does it make sense to upgrade to slightly stiffer diff bushings, or will the stock bushings be adequate? I already DIY'ed the M3 rear subframe bushings which greatly helped plant the rear end.

Two concerns I have with aftermarket bushings:

1. Whine noise inside the cabin. I will avoid solid bushings or harder poly compounds (see materials chart below). With the AKG DM9X9 95A medium durometer bushings, maybe the potential for noise is reduced. Hope they will blend in well with my M3 rubber subframe bushings already on the car. Here is the materials hardness chart from AKG Site:
   
   
2. Squeaking noises. Dont want to end up with this after a while. Car will be exposed to our Canadian winters with salt covered roads. Last thing I want to deal with regular maintenance/greasing of diff bushings. Perhaps squeaking is more frequent on suspension parts using poly bushings.

According to AKG chart, the 95A compound is half way between oem soft, and solid aluminum hard. Stiffness of the AKG 95A might be the way to go on a dual duty car.

Before I make a decision on bushings, I wanted you to help me choose:

1. Stock
2. Aftermarket
3. M3 fronts only (M3 rear diff bushing does not fit our diff)

Thanks.

[dcaron9999]

Contacted the fine folks at AKG Motorsport, and this is the response I received:

"Hello,

Upgrading to poly diff bushings will create a lot more diff whine, no matter which poly compound you upgrade to, the 75D or softer 95A.

Diff bushings, however, do not squeak (and you don’t lube them), so you don’t have to worry about that. But given your concerns about noise, I would probably suggest you stick with the OEM bushings.



Hope this helps.


Regards, ..."

[Dackelone]

I would use the diff bushing from an M3 IF it fits. ?

[dcaron9999]

Also received feebdack from HP Autosports:

"I would only replace those bushings if they are bad, but not worth the upgrade to the M version. If you already have the M3 subframe bushings, the next thing I would do is the M3 guide rods, then aftermarket toe arms with rod-ends."

[dcaron9999]

Originally Posted by Dackelone

I would use the diff bushing from an M3 IF it fits. ?

Only the two front ones are a direct replacement - the rear one is not. As per Harold at HPA, the M3 diff bushings are not worth the trouble. See previous post ...

[syclone2032]

i recently installed the Powerflex Black Series diff bushings. getting the old ones out requires some work, the poly bushings you just push them in, done.
no squeaking, diff whine is definitely audible but not too bad.

[Dr3K0]

Can you post a video of the diff whine?

[syclone2032]

Originally Posted by Dr3K0

Can you post a video of the diff whine?

i am abroad until the april 4th, after that i can try but i think the regular driving noises will not let it through in a video, in my car its just too subtle.
i got used to it pretty quickly.

[Dr3K0]

Originally Posted by syclone2032

i am abroad until the april 4th, after that i can try but i think the regular driving noises will not let it through in a video, in my car its just too subtle.
i got used to it pretty quickly.

Understood.

It seems the whine its very low. So, not a high pitch whine like a whimple supercharger? Or like a Tudor Series race car?

I want to have a good idea before jump into it. I will put a LSD and will replace the bushings. I'm between derlin and Powerflex black. I mainly use the car on the street but will start tracking soon; hopefully. I would hate to have dual whine. The diff and the wife.


Anyway, this is my weekend car and don't use it much. 2009 with 18k miles, still smell new.


Thanks
Dr3K0

[dcaron9999]

Originally Posted by Dr3K0

Understood.

It seems the whine its very low. So, not a high pitch whine like a whimple supercharger? Or like a Tudor Series race car?

I want to have a good idea before jump into it. I will put a LSD and will replace the bushings. I'm between derlin and Powerflex black. I mainly use the car on the street but will start tracking soon; hopefully. I would hate to have dual whine. The diff and the wife.


Anyway, this is my weekend car and don't use it much. 2009 with 18k miles, still smell new.


Thanks
Dr3K0

If you read posts #2 and #4 carefully (feedback from reputable vendors that sell diff bushings), you will learn that what is most important is firm rear subframe bushings. The stiffer differential bushings dont matter as much on our cars, and will bring a level of diff whine.

I got my Quaife 3.46 Final drive LSD installed in my manual 135i yesterday. My car is planted and has extra kick now (change from 3.08 to 3.46 final drive).

I have the M3 subframe bushings which I DIY'ed, and I chose to keep stock diff bushings. I track the car a lot, but still want a refined experience on the street.

[syclone2032]

not nearly as loud or as whining as a supercharger.

to clarify: i had the diff and the rear subframe out since i changed all the bushings and put an LSD in, i do not think i had changed the diff bushings if it hadn't been for the diff swap.
and i don't think urethane diff bushings will give you any noteworthy improvements.

[froop]

People have installed DEFIV differential lockdown kits. Basically it's an all aluminium kit that includes aluminium diff mounts as well as a plate to bolt the diff to the subframe. From what I have read of user reviews it doesn't seem to increase NVH much as long as you still have rubber bushings. Those cars have likely upgraded to M3 rear subframe bushings as well.

I have TMS solid aluminium subframe bushings in mine with M3 diff bushings in my M3 subframe and M3 LSD and I don't notice any diff whine. I personally wouldn't go for the DEFIV kit as I already have solid subframe bushings but if I were to have the M3 bushings I probably would have gotten the lockdown kit.

[Nugget]

Originally Posted by froop

People have installed DEFIV differential lockdown kits. Basically it's an all aluminium kit that includes aluminium diff mounts as well as a plate to bolt the diff to the subframe. From what I have read of user reviews it doesn't seem to increase NVH much as long as you still have rubber bushings. Those cars have likely upgraded to M3 rear subframe bushings as well.

I have TMS solid aluminium subframe bushings in mine with M3 diff bushings in my M3 subframe and M3 LSD and I don't notice any diff whine. I personally wouldn't go for the DEFIV kit as I already have solid subframe bushings but if I were to have the M3 bushings I probably would have gotten the lockdown kit.

I have the lockdown kit and the diff whine is noticeable but perfectably acceptable to me. There is a clunking that I am starting to get annoyed with.
I am contemplating going back to rubber bushings.
Maybe these and the stock front one. Or has anyone used these Powerflex ones?

[froop]

Originally Posted by Nugget

I have the lockdown kit and the diff whine is noticeable but perfectably acceptable to me. There is a clunking that I am starting to get annoyed with.
I am contemplating going back to rubber bushings.
Maybe these and the stock front one. Or has anyone used these Powerflex ones?

What rear subframe bushings are you using?

Also, what kind of clunking?

I know that when my axleshaft/diff bolts were loose I would get an intermittent clunking when changing gears, especially into first but once tightened it's all good.

I get a shitload of noise from my diff at the moment because I don't have the FM diff fluid in my M3 diff. Grinds and rubs like crazy going at low speeds, especially turning right.

[Nugget]

Originally Posted by froop

What rear subframe bushings are you using?

Also, what kind of clunking?

I know that when my axleshaft/diff bolts were loose I would get an intermittent clunking when changing gears, especially into first but once tightened it's all good.

I get a shitload of noise from my diff at the moment because I don't have the FM diff fluid in my M3 diff. Grinds and rubs like crazy going at low speeds, especially turning right.

I have M3 subframe bushings.
Clunking is mostly when slowing down to a stop, sometimes when getting off and on the throttle.
I have tightened down the bolts to the half shafts but I am going to try replacing them with new ones as the mechanics reused mine when switching diffs.

[froop]

Originally Posted by Nugget

I have M3 subframe bushings.
Clunking is mostly when slowing down to a stop, sometimes when getting off and on the throttle.
I have tightened down the bolts to the half shafts but I am going to try replacing them with new ones as the mechanics reused mine when switching diffs.

It's possible they could have loosened again. I noticed that when my mechanic retightened them and put threadlocker on them it stopped clunking however over the past week or so I think I'm starting to notice some of the clunking again. I haven't had a chance to lift the car up to check all the bolts but I'm assuming that they're loosening up again. I'll be replacing the bolts soon too.

[Nugget]

I was going to get under the car tonight anyway so will have a squiz. I don't have any torx sockets though.

[dcaron9999]

With all the issues caused by re-using half-shaft bolts, I figured I would spend an extra $40 and get 12 new stretch alloy BMW OE bolts (Part # 33-20-7-572-716 ), when I installed my Quaife 3.46FD in my 6-speed manual 135i.

I kept my original diff bushings/rear control arms/rear toe link, but upgraded to M3 rear subframe bushings.

I used 75W140NS RL fluid since my car will see the track a lot.

Rear end is now planted, makes no noise or clunking, whether at low or high speeds, hard or soft acceleration/deceleration, and tight or long sweeping turns...

[sour97]

I will install my powerflex diff. bushing (street version) and powerflex subframe insert with M3 arms. will report how bad the whine