335i rear end rebuild - diff and subframe bushings question

carabuser

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I was actually doing reading about the ediff earlier. The reason I disabled it is because I read a long thread on E90post years ago that mentioned that you needed to disable it when installing a LSD.

After doing more reading today I found a thread that discussed it in depth and the outcome was that it's best left enabled so I'll toggle it back on with ProTool next time I drive.
 
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pbondar

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I like your thought, and I don't know the answer. The only thing I have to add is that I'm under the impression e-diff actually makes a lot of intervention, even before big traction loss. I certainly could be wrong, I'm only under that impression because when I got my car CPO the sales guy was telling me about how the break pads wear faster from that, despite them supposed to not be wearing faster, because it's always applying break to adjust. Not sure if e-diff would be fighting the quaife or working together? It seems plausible the e-diff could be calibrated to play nice with the LSD though, if one knew how🤷‍♂️
The DSC system on the E89 aka DSC Mk60E5 has a number of functions as well as e-diff that rely on braking various wheels under various conditions...this from TIS

Functions familiar from current DSC:

  • ABS: Anti-lock braking system
  • EBV: Electronic brake force distribution
  • CBC: Cornering Brake Control
  • ASC: Automatic stability control
  • DTC: Dynamic traction control
  • MSR: Engine drag torque control
  • DBC: Dynamic brake control
  • RPA: Run Flat Indicator (not a driving dynamic control function)
  • CBS: Condition Based Service (not a driving dynamic control function)
New functions for DSC Mk60E5:

  • Brake Standby through pre-tensioning of the brakes in an emergency
  • Brake disc drying on wet roads
  • Fading compensation
  • Soft stop when braking to standstill (only E87 with 6-cylinder engine, E90, E91, E92, E93)
  • Start-off assistant
  • Adapted interface for cruise control with brake function (only E90, E91, E92, E93)
  • Adapted interface for active cruise control (only E90, E91, E92, E93)
So the brakes are used for..

BV: Electronic brake force distribution

EBV is a component of ABS and controls the brake force distribution between the front and rear wheels.

Advantage: Regardless of the load state of the vehicle, the best possible braking distance is achieved while driving stability is maintained.

Modern vehicles have relatively large brakes on the rear axle to shorten braking distances. To prevent the rear wheels from being overbraked in certain driving situations, EBV permanently monitors slip. EBV controls rear axle slip in dependence of the front axle.
CBC: Cornering Brake Control

CBC is an extension of ABS. CBC enhances driving stability if the brakes are applied when cornering.

Advantage: If the brakes are applied in a corner, optimum brake force distribution ensures optimum tracking stability.

When cornering, even very light braking can shift the axle-load distribution to the left or right so that driving stability is impaired. If required, CBC generates a stabilising load moment when the brakes are applied lightly outside the ABS intervention range.
ASC: Automatic stability control

ASC prevents the wheels from spinning when the vehicle is accelerating.

Advantage: Improved traction. The vehicle remains stable.

If one of the wheels of the drive axle is on a high-grip surface and the other is on a slippery surface, the wheel tending to skid is braked.

ASC also intervenes in the engine control (to reduce the ignition angle, injection quantity, throttle valve setting).

So it could be that the rear discs are used extensively in those situations..certainly my rear pads wear out far faster than the front ones...
 
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Cruizinmax

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Personally, having driven my wavetrac equipped car with and without the e-diff disabled, definitely recommended leaving it disabled. With it enabled you can still feel the car twitching around when accelerating around corners or even in a straight line. The e-diff intervenes far before "major" wheel slip happens. I imagine that when the brakes are being applied it is changing the geometry enough through the flex in the bushings, it's is essentially steering the car and it oscillates left to right multiple times per second.

Regarding the "drawback" of quaife, does anyone find themselves with wheels airborne trying to accelerate hard often?? There are videos out there of quaife equipped cars with one wheel on ice and the car accelerating away completely normally. Seems like a non-issue to me.
 
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pbondar

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Personally, having driven my wavetrac equipped car with and without the e-diff disabled, definitely recommended leaving it disabled. With it enabled you can still feel the car twitching around when accelerating around corners or even in a straight line. The e-diff intervenes far before "major" wheel slip happens. I imagine that when the brakes are being applied it is changing the geometry enough through the flex in the bushings, it's is essentially steering the car and it oscillates left to right multiple times per second.

Regarding the "drawback" of quaife, does anyone often find themselves with wheels airborne trying to accelerate hard often?? There are videos out there of quaife equipped cars with one wheel on ice and the car accelerating away completely normally. Seems like a non-issue to me.
I noticed the ro-ro-ing under reasonably hard acceleration when the car was 400 BHP 650nm on damp roads..I can’t remember at that time whether the e-diff was coded on or off..the frequency was more like 2-3 seconds as it fed power (or braked ) each wheel…come the other side of winter I think I’ll just have to try a back to back test on my ‘private test track’…😂

Certainly on my E89 at 12 years and 60k miles I was definitely getting rear steering from the RTABs flexing and changing toe in /toe out..🤔

Now with uprated RTABs and fresh other uprated rear bushes I don’t be that feeling come what may..👌

I was being an agent provocateur with regards to previous posters disparaging comments on the limitations of the Quaife vs anything else..plated, Dexler, Wavetrac etc etc.. 😳🤔😂🙈

I look forward to every bodies testing in scientific conditions of LSD/ e-diff on ..off👌
 

CalvinNismo

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Nov 1, 2020
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I can echo Cruizinmax’s experience. Wavetrac with E-diff’ on would jab brakes at the wheel too late, the ATB had already biased torque to the other wheel, it would then jab at the other wheel repeating the process side to side until in my case throwing up an ABS error it got so confused. Wasn’t nice, made the car very unsettled. I haven’t been able to replicate the experience since coding off the E-diff’. My tuppence.
 

pbondar

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Interesting comment from these diff ‘experts

Brake Based Electronic Differentials​

Brake based electronic differentials are not true limited-slip differentials, however they rely on similar technology to torque vectoring differentials. Instead of reducing torque to the spinning wheel, the brake is applied to slow it down. As the differential is a standard open differential, when a brake is applied to the spinning wheel it creates a false sense of grip, allowing equal amounts of torque to be transferred to the wheel with grip. Whilst this does remove some of the downsides to an open differential, the wheel being braked still does not transfer that torque to the ground.

When compared to a torque vectoring differential, brake based differentials sap power, and aren’t as efficient. However they are better than open differentials, and might be the difference between getting stuck in mud or not. Fortunately upgrading them with an ATB is an excellent choice, and greatly improves their performance. ATB’s work very well with brake based LSDs as only a small braking force has to be applied to the spinning wheel in order for lots of torque to be transferred to the one with grip.

https://www.rrtransmissions.com/technical/limited-slip-differentials
 

RTA

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The e-diff is an over reactive brake eating little monster and heat generator ;-) .
It brakes while you want to accelerate.
In my experience on road and street, you can drive safely without the e-diff. Abs and the other friends will take care.
Tyre setup, alignment and the right spring/damper settings have much more impact.
 
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carabuser

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@carabuser when are the BBS LM’s coming with some proper meats 🙂
BBS LMs are 🤮

I don't really like aftermarket wheels at all, with the exception of the BBS CH. They are usually £4k a set for quality forged wheels and aftermarket cast wheels are always trash. Luckily on the Z4 the 437M wheels fit perfectly, but I don't think they work on the E92.

Is there any OEM forged wheels from other cars that fit the E92? Or any OEM cast wheels that are 18" and 9j that will work?
 

JohnDaviz

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M513
iche-513-M-BMW-M3-F80-M4-F82-F83-18-Zo_1-1155x1155.jpg
 
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carabuser

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513Ms are rare but I'll keep an eye out for them.

I've seen sets sell for £900~ including nearly new tyres so I'll keep an eye out. Can't really get any better value than that for proper forged wheels.
 

JohnDaviz

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That is why i have a set with Nankang AR-1 waiting to be mounted :D Got them for a great price and they look just perfect. Probably my favourite wheel for my e92.
 

SLOWESTN54

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One of my friends has 513M's on his F80, great choice of wheels.👍I'm still pissed that they switched to 5x112 with the G Series cars, cant use any of the old M wheels.
 

AzNdevil

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inner wheel lift does happen when you are driving on roads/courses that arent smooth or riding curbs on a racetrack
this is highly dependent on your car ride height, spring/swaybar stiffness, tire traction and negative travel of the damper

generally speaking wheel lift is not a good thing unless you are driving a fwd hatchback (eg. renault clio 172/peugot 205)

on an open/quaife/mf/helical diff, you will know when it happens with the car suddenly reving faster when you are on the accelerator but doesnt seem to be accelerating for a split second

anyways, my recommendation is, keep ediff off and try disabling ASR from tune for you want to go all out. brakes will still grab to force the car where your steering is pointing to but its somewhat more natural

https://www.spoolstreet.com/threads/disabling-dcs-torque-reduction-for-road-course-track-tune.8558/