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      08-22-2011, 07:52 PM   #23
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I was going to do a little write up on this, but I will post a little bit of info in here.

This happened to me on my 2011 E92 M3.

Differential bolt snapped and sheared off, the differential fell down to one side and bent the subframe differential mounts.

Took car into the dealership, they told me to take a hike. I called BMW NA, they gave me some trouble too. I wrote a technical letter to them and one of their engineers explaining that this is not normal under any circumstance, especially since they were blaming the problem on a non OEM exhaust system (doesn't make any sense).

After 2 weeks of hassle and going back and forth with my car sitting there doing nothing, they finally decided to do the repairs on their own bill. The replaced the subframe, the differential and CSB. (All brand new)

They didn't do a proper job of aligning the subframe (rear axle carrier to be proper) into the unibody. I had to create a tool which centered the RAC to the unibody and center it. They also installed one rear spring upside down in which I corrected myself quickly.

I urged them to send the failed parts back to BMW in Germany for analysis, and they did. I also wrote another technical letter to BMW AG explaining the situation and giving possible improvement for the RAC. So far I have been told that the bolt was possibly defective but I felt that this was highly unlikely and it was do to compliance in the subframe differential tabs.

During this situation, I have analyzed the rear subframe myself, and have decided to design a rear subframe reinforcement kit and offer it to the public in due time.

-Malek
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      08-23-2011, 01:33 AM   #24
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Quote:
Originally Posted by Malekreza11 View Post
I was going to do a little write up on this, but I will post a little bit of info in here.

This happened to me on my 2011 E92 M3.

Differential bolt snapped and sheared off, the differential fell down to one side and bent the subframe differential mounts.

Took car into the dealership, they told me to take a hike. I called BMW NA, they gave me some trouble too. I wrote a technical letter to them and one of their engineers explaining that this is not normal under any circumstance, especially since they were blaming the problem on a non OEM exhaust system (doesn't make any sense).

After 2 weeks of hassle and going back and forth with my car sitting there doing nothing, they finally decided to do the repairs on their own bill. The replaced the subframe, the differential and CSB. (All brand new)

They didn't do a proper job of aligning the subframe (rear axle carrier to be proper) into the unibody. I had to create a tool which centered the RAC to the unibody and center it. They also installed one rear spring upside down in which I corrected myself quickly.

I urged them to send the failed parts back to BMW in Germany for analysis, and they did. I also wrote another technical letter to BMW AG explaining the situation and giving possible improvement for the RAC. So far I have been told that the bolt was possibly defective but I felt that this was highly unlikely and it was do to compliance in the subframe differential tabs.

During this situation, I have analyzed the rear subframe myself, and have decided to design a rear subframe reinforcement kit and offer it to the public in due time.

-Malek
Interested in your invention and the analysis which led to it being created! Good luck!
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      09-14-2011, 12:08 PM   #25
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I experienced the same issue earlier this week. A bolt sheared and twisted the diff. On the way to the dealership, the loose parts opened the rear left break line and I lost brakes (almost crashed). I made it to the dealership pumping the break pedal and using the hand brake. The dealer told me that they won't cover it because I have the Akra slip-on and that's what caused the shear in the bolt. This exhaust's weight is roughly half of the stock exhaust... I did not expect that kind of treatment from BMW.
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      09-14-2011, 02:10 PM   #26
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Quote:
Originally Posted by Em Trey Drvr View Post
I did not expect that kind of treatment from BMW.
Why do you expect them to cover a mistake made by the exhaust installation shop (or whoever installed it)? The most likely root cause of the failure was improper retorquing of those bolts. Most shops just remove those brackets, rather than fiddle with the rubber mounts, which are difficult to dislodge up there.
Another failure cause (not applicable to you) is to use the subframe as a lever to remove springs, rather than using proper spring compressors. Good luck man.
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      09-14-2011, 02:44 PM   #27
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Quote:
Originally Posted by Em Trey Drvr View Post
I experienced the same issue earlier this week. A bolt sheared and twisted the diff. On the way to the dealership, the loose parts opened the rear left break line and I lost brakes (almost crashed). I made it to the dealership pumping the break pedal and using the hand brake. The dealer told me that they won't cover it because I have the Akra slip-on and that's what caused the shear in the bolt. This exhaust's weight is roughly half of the stock exhaust... I did not expect that kind of treatment from BMW.
Disturbing to see yet another failure.

Any update Malekreza? : )
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      09-14-2011, 08:13 PM   #28
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what is the correct torque specs for these bolts?
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      09-15-2011, 12:23 PM   #29
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Quote:
Originally Posted by elp_jc View Post
Why do you expect them to cover a mistake made by the exhaust installation shop (or whoever installed it)? The most likely root cause of the failure was improper retorquing of those bolts. Most shops just remove those brackets, rather than fiddle with the rubber mounts, which are difficult to dislodge up there.
Another failure cause (not applicable to you) is to use the subframe as a lever to remove springs, rather than using proper spring compressors. Good luck man.
There are no spring compressors or leveraging required to do the rear springs. You undo 2 bolts and the spring pops out. Both bolts are irrelevant to the subframe and differential.

I was actually on the phone for about 1.5 hours yesterday trying to come up with a solution with BMW and BMW NA regarding this. This is beginning to get out of hand and kills any confidence people may feel in driving their cars.

Singletrack, yes I do have some updates. I have already designed the reinforcements and will begin to test them sooner than later.

I am also working on fastening solution that will improve on the mounting of the differential so it minimizes differential movement and compliance which causes damaging of the bolts.

I have also realized that stiffening the axle carrier (subframe) bushings such as the GTS, etc will reduce the chance of compliance in the system and keep the subframe from moving around and causing wheel hop which is the primary cause of this.
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      09-15-2011, 01:10 PM   #30
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Cool, thanks. Looking forward to more updates!
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      09-16-2011, 10:32 AM   #31
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Quote:
Originally Posted by Malekreza11 View Post
There are no spring compressors or leveraging required to do the rear springs. You undo 2 bolts and the spring pops out. Both bolts are irrelevant to the subframe and differential. .
Thanks for the heads up. I just mentioned that as a sidenote because I read several times of people using the subframe as a LEVER (bolts have nothing to do with that indeed) to install springs, so maybe they were doing it wrong . But the issue here is that most of the failures seem to originate from BAD INSTALLATIONS (like exhaust brackets removed by shops), and abuse, not by a defect.

Furthermore, seems like you're trying to make it a more serious issue than it actually is to sell your part. Unless you abuse the crap out of your car, such as hard launches causing wheel hop (something it was NOT designed to withstand), or a shop doesn't torque the bolts properly after being removed, car is perfectly fine. Just look at the few cases out of thousands and thousands of cars produced. Good day.

Last edited by elp_jc; 09-16-2011 at 10:40 AM.
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      09-16-2011, 11:34 AM   #32
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Quote:
Originally Posted by elp_jc View Post
Thanks for the heads up. I just mentioned that as a sidenote because I read several times of people using the subframe as a LEVER (bolts have nothing to do with that indeed) to install springs, so maybe they were doing it wrong . But the issue here is that most of the failures seem to originate from BAD INSTALLATIONS (like exhaust brackets removed by shops), and abuse, not by a defect.
You don't know that. I use to think that also, but the large number of failures has me wondering. It's also pretty difficult to make that assumption without examining the failures. There really are few details of the failure; all we have is info on the aftermath.

Quote:
Furthermore, seems like you're trying to make it a more serious issue than it actually is to sell your part. Unless you abuse the crap out of your car, such as hard launches causing wheel hop (something it was NOT designed to withstand), or a shop doesn't torque the bolts properly after being removed, car is perfectly fine. Just look at the few cases out of thousands and thousands of cars produced. Good day.
Please. First of all - reinforced bushings are a common enhancement to many aftermarket cars. If he were in such a rush to gouge us, he probably would have a half-assed product to market by now.

The car comes with launch control, so it is intended to be launched. I would agree that if you have dramatic, and repeated, wheel hop then you are asking for trouble. But that applies to all cars really.
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      09-16-2011, 03:26 PM   #33
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Quote:
Originally Posted by elp_jc View Post
Thanks for the heads up. I just mentioned that as a sidenote because I read several times of people using the subframe as a LEVER (bolts have nothing to do with that indeed) to install springs, so maybe they were doing it wrong . But the issue here is that most of the failures seem to originate from BAD INSTALLATIONS (like exhaust brackets removed by shops), and abuse, not by a defect.

Furthermore, seems like you're trying to make it a more serious issue than it actually is to sell your part. Unless you abuse the crap out of your car, such as hard launches causing wheel hop (something it was NOT designed to withstand), or a shop doesn't torque the bolts properly after being removed, car is perfectly fine. Just look at the few cases out of thousands and thousands of cars produced. Good day.
If I wanted to make money off the people on this forum for something like you are claiming, I would have released something that was a half way done job with no proof that it improves anything.

I have been building very high HP cars for a very long time now. Reinforcing the subframe is a common practice, ESPECIALLY on BMW's. This wouldn't be the first BMW, or M3 for that matter that has a subframe prone to damage from usage.

As of right now, I am testing my designs to see if it will even work or not. There are MANY cars out there with this catastrophic failure now.

Thank you for your input, however, even removing the exhaust brackets from the car and improperly torquing them wouldn't cause this failure. The failure is caused from the loosening of the main differential bolt, it then begins to shear itself until broken or in some cases, it doesn't shear, it simply falls out. What then happens is the differential is clocked to a degree that it damages the 2 front differential mounts and damages the subframe.
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      09-16-2011, 06:49 PM   #34
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I checked my bolts last weekend, and they were loose! I could almost have undone them by hand. I tightened them up good, and will now check them periodically as a matter of course.
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      09-16-2011, 08:39 PM   #35
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Quote:
Originally Posted by bigeye View Post
I checked my bolts last weekend, and they were loose! I could almost have undone them by hand. I tightened them up good, and will now check them periodically as a matter of course.
Scary.

Have you done any work back there previously?
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      09-16-2011, 11:48 PM   #36
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Quote:
Originally Posted by bigeye View Post
I checked my bolts last weekend, and they were loose! I could almost have undone them by hand. I tightened them up good, and will now check them periodically as a matter of course.
That's scary man. Any mods on your car, especially an exhaust? And if yes, who installed it? You might want to avoid that person/place if that was the case. Oh, and find out what's the right torque on those bolts man; don't do a half-a$$ job on that. Good luck.
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      09-16-2011, 11:58 PM   #37
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Quote:
Originally Posted by Malekreza11 View Post
Thank you for your input, however, even removing the exhaust brackets from the car and improperly torquing them wouldn't cause this failure.
WIth TWO out of THREE bolts loose it wouldn't cause a failure? Come on man; it's simple common sense (it's like saying you only need 2 out of the 5 lug bolts on your wheels). And again, that bolt up there is not going to loosen by itself if properly torqued without abuse. Yes, I know our subframe is not bulletproof by any means, but a lot beefier than previous iterations, and plenty strong for its intended use. You can't expect BMW to build a freaking tank just for the very few who want to abuse it with drag races and such. Yes again, if you're one of those guys, it'd definitely help to beef the subframe, and am glad you're providing a solution, but you folks are in the ultra minority. Just count the cases of subframe failures (probably with 2 hands), and divide them by the tens of thousands of cars already produced, and tell me if it's a chronic problem people should worry about. And most of those cases involved either abuse and/or negligence from a bad install job.

Bottom line is this car is far from perfect, but a weak subframe is NOT one of its issues. Have a good one folks.

Last edited by elp_jc; 09-17-2011 at 12:04 AM.
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      10-13-2011, 03:34 AM   #38
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Quote:
Originally Posted by elp_jc View Post
That's scary man. Any mods on your car, especially an exhaust? And if yes, who installed it? You might want to avoid that person/place if that was the case. Oh, and find out what's the right torque on those bolts man; don't do a half-a$$ job on that. Good luck.
I installed Akra exhaust myself, but did not remove the hangers, hence did not touch those bolts.
I noticed a few clunks, hence checked it out - just in time!
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      10-13-2011, 10:34 AM   #39
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better check mine later... i have an akra as well but its been there for quite some time...

can anyone show a shot of this bolt we are talking about. i just want to make sure. thats all
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      10-19-2011, 01:00 PM   #40
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as someone asked above already, what are the torque spec on these bolts? anyone know?
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      10-19-2011, 05:34 PM   #41
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Quote:
Originally Posted by e92zero View Post
as someone asked above already, what are the torque spec on these bolts? anyone know?
The smaller of the bolts which break on the rear differential are torqued to 100 nm or 74 ft/lbs.

The large diff bolt is torqued to 165 nm or 122 ft/lbs.

Does anyone know if these bolts are aluminum?

I also had a clunking from the rear end and found my two smaller diff bolts loose, not enough to move them by hand, but not torqued to spec. If the bolts are aluminum, that could certainly be an issue (as far as breakage) if the proper torque is not used.

Last edited by Zba; 11-14-2011 at 04:27 PM. Reason: updated torques
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      10-19-2011, 08:13 PM   #42
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      10-20-2011, 04:00 AM   #43
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^Zba, thanks for the torque spec. I am gonna check these bolts in a week or so when i change the motor/transmission/diff oil.
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      10-20-2011, 12:34 PM   #44
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