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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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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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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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Any update Malekreza? : ) |
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09-15-2011, 12:23 PM | #29 | |
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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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09-16-2011, 10:32 AM | #31 | |
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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 JCtx; 09-16-2011 at 10:40 AM.. |
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09-16-2011, 11:34 AM | #32 | ||
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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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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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09-16-2011, 11:48 PM | #36 |
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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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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 JCtx; 09-17-2011 at 12:04 AM.. |
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10-13-2011, 03:34 AM | #38 | |
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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, 05:34 PM | #41 | |
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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 03:27 PM.. Reason: updated torques |
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