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      08-14-2012, 03:39 PM   #89
kiloil
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Quote:
Originally Posted by mitch32 View Post
BMW Canada contacted me, took down additional information and never called me back. I got irritated over this past weekend so I decided to tear down the rear of the car. The diff is 100% in good shape, the aluminum on the back of the diff broke. When that happened the yoke of the driveshaft broke and the subframe got dinged. I ordered all the parts today and will install them over the weekend, I will be sueing BMW Canada for time lost and parts/labour.

tibra1 you seem like a fairly knowledgable guy, the fact the rear casing broke off the car is ludacris. I have been working on cars for 15 years++, as a mechanic, an engineer, and as a enthusiast. I have never, not once (minus the e36 m3, thats a different story) seen a diff fall off a car. I've seen transmissions split, subframes twist, transmission crossmembers break, you name it I've seen it. A diff should never fall off a car, stock street car or not. You should be able to break axles, driveshafts, burn ring gears/spurs before a diff falls off a car. A burnout essentially should never break anything since theres no real load, on the other hand wheelhop can break many things but not a diff housing. The m3 rear housing is the weidest most unintelligent design I've ever witnessed on a car (many bmw's are like this, I'm guessing to eliminate NVH but from a durability/reliability standpoint the design is faulty). The bolts are also in shear which is a terrible design, should be in tension since a bolt is strong that way, why is there only 1 bolt on top? Anything that requires any real strength will have the bolts in tension/compression, its design/engineering 101. Also aluminum fails without a doubt, putting 1 bolt and no re-enforcement will cause it to break. Since aluminum fails (fatigue limit) Aluminum wings on airplanes are constantly x-rayed and tested for cracks. You can deisgn aluminum in ways that it never sees extreme loads but obviously that didn't happen with the e92 m3. Solid bushings will help alleviate some of the fatigue, a brace seems like the best option.
You should have never torn down the rear of the car. It may have been going slowly, but there was some progress it sounded. Good luck on being reimbursed.
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      08-14-2012, 03:53 PM   #90
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Originally Posted by tibra1 View Post
Your posts are rife with misinformation and takes away focus from the real issue. The bolts are not at fault here, rather the rubber mounts that house the bolts which flex. Several performance shops have already developed solid or delrin cased mounts which unitize the diff to the sub-frame and eliminate the flex caused by the diff during hard driving.

So you argue the bolts are at fault? Yet these shops who have spent the time and effort to CNC the uprated diff mounts have not also machined new bolts to go along with their mounts????????? you would think machining bolts that are partially threaded wouldn’t be too complicated for them to do right? Yet they haven’t. :

The reason they have not and no one else has is there is no need for using partially threaded bolts if you unitize the diff to the rear sub-frame with solid or stiffer mounts than OEM. So fortunately we don’t have to wait for someone to machine these in their garage b/c the use of these bolts is moot if you use the solid mounts. Again as with all suspension stiffness uprating there will be some measure of NVH increase.
Using a fully threaded bolt in single shear where only one of the parts is threaded is poor detailing. The threaded portion of the bolt should be excluded from the shear plane. If including the threads in the shear plane is unavoidable then the bolt capacity should be determined using the root thread area instead of the gross bolt area.

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Originally Posted by mitch32 View Post
The bolts are also in shear which is a terrible design, should be in tension since a bolt is strong that way, why is there only 1 bolt on top? Anything that requires any real strength will have the bolts in tension/compression, its design/engineering 101.
Bolts designed to resist shear are completely acceptable and standard in the engineering world. You've probably driven over many bridges where the steel girders are spliced together with nothing but bolts in shear. Check the AISC Steel Manual that structural engineers use to design steel structures, they have page after page of tabulated shear resistance values for different types of bolt/bolt groups/eccentric loadings to make connection design easier.

Last edited by oldmanstyle; 08-14-2012 at 04:02 PM.
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      08-14-2012, 04:12 PM   #91
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Originally Posted by oldmanstyle View Post
Bolts designed to resist shear are completely acceptable and standard in the engineering world. You've probably driven over many bridges where the steel girders are spliced together with nothing but bolts in shear. Check the AISC Steel Manual that structural engineers use to design steel structures, they have page after page of tabulated shear resistance values for different types of bolt/bolt groups/eccentric loadings to make connection design easier.
You are definetely not wrong but it is ideal for all fasteners to be in tension. Depending the bridge, the bolts are taking very little of the load and if they are, there are many bolts and they are almost all in shear. On a bridge there are no "Jesus" nut/bolts (helicopter term, sorry), meaning if one bolt fails the whole bridge won't collapse. The m3 diff has a "Jesus" nut/bolt on the top. I personally feel its bad design, but the engineers at BMW have much more experience then me and there is definetely a reason (maybe its for the simple reason that they want it to fail, or cost came into affect). If there was re-enforcement and a second bolt, I strongly feel the diff wouldn't have broken, look at every other IRS car and they have more then 1 bolt on top (4 botls total at a minimum).
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      08-15-2012, 05:41 PM   #92
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The guys that are suggesting that the OP is in the wrong for doing a burnout and that he should be left out to dry is laughable. A 414 HP sports car should be built to handle this "abuse."

I redline my E92 m3 every time I get in it and I don't think what I am doing is abuse. I don't burn out intentionally because burn outs aren't really my thing but to think that you should go easy on a car like this so it doesn't break is rediculous.
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      08-15-2012, 08:01 PM   #93
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Id like to report a successful burnout. Everything is still attached to the car. Ftmfw!
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      08-16-2012, 08:26 AM   #94
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Originally Posted by Space Ghost
Id like to report a successful burnout. Everything is still attached to the car. Ftmfw!
That's the confidence I expect from an m3 owner, my confidence in the m3 is not in existence at this point.
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      08-20-2012, 07:50 AM   #95
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Yea, I can't believe they aren't atleast doing something... The so called "abuse" happened 2000km before my actually diff fell out of the car...

I also own a 1990 Nissan GTR running 600hp and I've driven many times on the drag strip, and circuit, the diff never broke (nothing in the drivetrain besides the clutch actually broke). The diff, axles, driveshaft, are all stock.... Why did a 2008 m3 diff fall out of the car? The m3 should be able to handle its stock power even under abuse, there are limits to abuse I mean bouncing off the rev limiter, clutch kicking, and wheelhop will eventually break things but for an m3 should be able to handle pretty much anything. One of my buddies has an e46 m3, it has been a dedicated track car, is abused almost every day it is driven, and is pretty much stock, it has never had a major issue like this. My e92 was never really abused as such, I've never done a burnout, the only thing I've done is gone full gas from a stop but not a launch with a clutch drop... and no launch control either.

I am truly appalled at the BMW dealerships real lack of willingness to resolve the issue with BMW Canada. BMW Canada denined the claim, should it stop their? I bought the car from the BMW dealer thinking that because I bought it from them they would essentially take care of any of my issues and try to keep me as a customer.

The dealership flat out lied to me multiple times... BTW the dealership also told me the car was never winter driven, with a rusted subframe as such I believe it definitely was. Shame on me for not looking under the car before I bought the car but I thought buying from a BMW dealership with a certified warranty from BMW Canada annulled any reason to actually look under.

Truly disappointed with BMW and the dealership.
Out of curiosity... Are your wheels and tires stock?
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      08-21-2012, 06:16 PM   #96
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this is some gtr launch control/skynet shit. and part of why the cars i'll be buying will be from the 20th century, save something italian or a porsche v10
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      08-23-2012, 10:07 AM   #97
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Out of curiosity... Are your wheels and tires stock?
The car is 100% stock, PS2 tires on 19" wheels.
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      08-23-2012, 11:54 AM   #98
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I will take a picture of mine with 70K + miles and still looks brand new...
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Do you drive in the salt brine & snow like those who drive their M's in a Canadian winter?Looks pretty normal for a 4 year old winter driven car in Eastern Canada.
I drive my car in the north east winter. Still looks brand new.
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