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      10-09-2010, 10:05 PM   #1
stE92M3
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E92 M3 broken differential bolt

Hopefully this is informational if your E9x M3 6MT (or DCT) is making new weird sounds. Sorry for the long article but I wanted to be clear.

This week was somewhat unpleasant. At ~11.5K miles, on last Saturday, the car started to make weird "popping" sounds from the back. The sounds would happen sometime during a shift, after a shift or just decelerating/coasting/engine braking between 2-3K RPM. This was not the usual clutch/flywheel judder/shuddering sound that this performance car is supposed to make.

I took the car in on Tuesday and was unable to duplicate the sound the on a test drive with a chief mechanic at the dealership. After driving the car, they recommend a diff fluid change to some new compound based on some BMW SIB (under warranty). On Tuesday evening, the car seems a lot more smoother to shift/drive. The sound no longer shows up. Diff fluid magic?

Wednesday: Car not driven

Thursday: At the end of a 50 mile trip (with 2 stops), 1 mile away from my garage, the car suddenly makes a loud grinding/metallic/holy-S$!t sound. It is like taking 2 metal garbage can lids and rubbing them against each other at high rotational velocities; coming from the back of the car. Car will shift, drive silently at slow speeds. Scary-ass-transmission-sounds-screwed sound at 2-3K RPM especially when coasting. I though the transmission was a goner.


Friday: I take the car in at 8AM. I haven't seen 8AM in like 6 months! Sound stops on the 1.5 mile drive to the dealership from my home. On a test drive with the shop foreman, unable to duplicate the sound again. WTF - felt like I was losing my mind and hearing things. I leave the car with the foreman and let him drive it all day while I was at work. On the 4th drive, (he seemed to have driven the car 10-15 miles that day), he was able to make the car make that sound after a hard turn.

After raising the car on the lift, they notice that the left hand side differential bolt has broken through clean:

http://www.realoem.com/bmw/showparts...=33&fg=05&hl=4

(Part M12X100-10.9 on the left hand side)

According to the techs/shop foreman: either the bolt was torqued incorrectly or the metal was bad(das german engineering quality control?). They even showed me the broken bolt later when I picked up the car (much appreciated).

The diff bolt was replaced after removing and remounting the diff, torquing everything back there correctly. They overnighted the part (2 dollar bolt!) and I had the car on Saturday afternoon. Quick!

As a side effect, the "judder"/shudder, 2nd gear notchy feeling and occasional feeling of shifts/clutch not being smooth have gone away. The clutch feels a lot lighter, the shift sounds are almost gone. The car feels new and different and just smooth overall! The dealership seems to have done an awesome job, took the time to explain things to me. It seems all the other parts around are not damaged due to the broken bolt. Time will tell.

It seems some other E9x owners and some E46 owners have had differential mounting bolt issues. Sucks but I guess its a performance car and stuff breaks.
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      10-09-2010, 10:48 PM   #2
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Hey man, glad your problem was corrected, but that bolt (#2) you mentioned just supports the exhaust, not the differential . Maybe bolt #4, which is a beefier M14. At any rate, that's weird man. Have you tracked your car?
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      10-09-2010, 10:56 PM   #3
stE92M3
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Thanks. To be more clear:
Bolt #3 on the car's left hand side (not diagram's letf) broke and the diagram shows it mounts to the diff. It actually caused the diff to move a little causing more noise. It mounts the diff to some part of the car( perhaps connecting it to some part of the exhaust system). Part number: 33176760343 (Hex bolt with Washer). The invoice also calls it "LOWER DIFF BOLT" (and matches up with the part number #3 in the diagram). Yes it is a pretty beefy looking bolt so it was somewhat worrisome it broke.
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      10-10-2010, 04:55 PM   #4
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Quote:
Originally Posted by stE92M3 View Post
Bolt #3 on the car's left hand side (not diagram's letf) broke
Bolts #2 and #3 are identical, and all they do is support the exhaust pipe brackets (left and right) to the differential, so don't worry; it's nothing serious. The orange hangers attach to those brackets and the exhaust pipes. The bracket was just making a racket against the differential (or pipe possibly touching driveshaft), but it's definitely not the differential itself. It's weird that the bolt just broke when there's little stress on it. Glad it wasn't a more important bolt.
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      10-22-2010, 11:56 AM   #5
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Quote:
Originally Posted by elp_jc View Post
Bolts #2 and #3 are identical, and all they do is support the exhaust pipe brackets (left and right) to the differential, so don't worry; it's nothing serious. The orange hangers attach to those brackets and the exhaust pipes. The bracket was just making a racket against the differential (or pipe possibly touching driveshaft), but it's definitely not the differential itself. It's weird that the bolt just broke when there's little stress on it. Glad it wasn't a more important bolt.
Actually no.

The two front bolts that go through the exhaust hangers also go through the rubber isolated mounts on the crossmember.

There are only three bolts holding the differential on, two smaller diameter in the front and one larger one on the rear. I am under the car right now looking at it
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      10-22-2010, 02:03 PM   #6
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I've had this same Issue, except I had some transmission damage occur from it and they replaced the bolt + transmission
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      10-23-2010, 12:10 AM   #7
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Dang.. I hope this doesn't become a widespread issue.
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      10-29-2010, 06:46 PM   #8
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I Am Having This Issue Rite Now, Roadside Is On There Way....how Long Did It Take To Fix?.........btw Was The Noise You Were Hearing After Shift Like A Loud Banging Noise ( Almost Sounds Like The Back End Is About To Come Rite Off)
Please Reply Asap Im Freakin Out
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      10-29-2010, 07:38 PM   #9
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Wow, this thread is spooky scary.
My car has 9K miles.
Should I have the dealership check for these bolts?
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      10-29-2010, 08:23 PM   #10
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does the sound come from the back of the car during a hard acceleration? becasue that has happened to me almost like a bang ( not a backfire ) like a bolt being hit with a hammer?
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      10-29-2010, 09:04 PM   #11
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yeah a very loud bang....i also heard a very loud grinding noise so i pulled over and had it towed

lets see what the dealer says in the AM
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      10-29-2010, 11:34 PM   #12
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Quote:
Originally Posted by KJM3 View Post
There are only three bolts holding the differential on, two smaller diameter in the front and one larger one on the left rear. I am under the car right now looking at it
I stand corrected. Got under the car too, and that's indeed the case.

Man, I don't doubt these cases, but shearing a bolt that thick with surfaces next to each other is unheard of, especially with a differential. Have you guys done any launches? Could somebody post pictures? Wonder if we should replace ours as a precaution . Or is it abuse? It still shouldn't happen though; usually shaft splines are the weak link.

Last edited by elp_jc; 05-18-2011 at 12:14 AM.
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      10-31-2010, 04:35 PM   #13
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Quote:
Originally Posted by JETonFOX View Post
yeah a very loud bang....i also heard a very loud grinding noise so i pulled over and had it towed

lets see what the dealer says in the AM
I didnt hear a loud bang, just telltale "pop"ing sounds before it gave way to the grinding. Good luck with your fix.
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      11-01-2010, 03:18 AM   #14
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My friend had this problem in hi e9x m3 with 6mt. Its been said that these e9x m3's are nowhere near as stout to take the abuse as the e46's. Upon taking the car to Sam@Autotalent, he said this has happened to a few of his clients already. The bolt has to be ordered from Germany and the bracket could also get easily damaged. In my friend's car, he has repeated launches, and upon many many WOT runs, shifted hard and fast. The weight transfer made the bolt go out. Sam also said his subframe was slightly tweaked. This problem is happening to mostly 6mt owners apparently. A clunk noise could be heard, and the dealer will not back up the damage because of repetitive launches or mods. It is easier to take it to an independent service shop.
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      05-17-2011, 03:47 PM   #15
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This has happened to me already and they replaced the bolt under warranty...and after 5k miles, I have another broken bolt. Woo Hoo!

Off to the dealership
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      05-21-2011, 12:10 AM   #16
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Quote:
Originally Posted by Dustin@AEperformance View Post
This has happened to me already and they replaced the bolt under warranty...and after 5k miles, I have another broken bolt. Woo Hoo!
Man, that's the first time I ever hear of bolts of that size just shearing off . Are those bolts TTY? Have you drag-raced your car? Just can't imagine what could be putting the kind of stress to shear a bolt off like that. Thanks for the update.
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      08-22-2011, 02:32 AM   #17
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this has also happened to me twice! and the car only has 5K miles first it was the exhaust bolt and then less then 1K miles later the diff bolt. witch made the diff fall and bent the rear subframe. would this pass for a lemon law if it happens again? i really dont feal safe in this car. and my 2 y.o. daughter is with me 98% of the time and now i dont even want to take her in the car! this is somthing that should not be happening with a 70K car!
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      08-22-2011, 09:33 AM   #18
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This definitely appears to be a trend.
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      08-22-2011, 11:04 AM   #19
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I can't imagine that these fastners are torque to yield fastners. The bolt isn't even loaded in tension like a head bolt, but in double shear. I wonder if it's shearing more from vibration than from actual constant load.
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      08-22-2011, 05:08 PM   #20
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Quote:
Originally Posted by Ilia@IND View Post
I wonder if it's shearing more from vibration than from actual constant load.
They're rubber-mounted, so I'd say that is extremely unlikely. It could happen, but only on a defective bolt IMO, not as a root cause by itself. I'd also rule out excessive torque, as you'd need a crapload more than normal to cause tensile failure on such a big a$$ bolt. Unfortunately, I don't expect posters to tell us the truth for fear of BMW/dealers reading this forum and denying warranty, so we have to take those posts with a grain of salt (understandable). Here are the most likely causes IMO:

- Owner abuse in the form of axle-hop, repeated launches, etc.
- Missing or loose bolts from an exhaust installation
- Bad aftermarket spring job, where installer uses diff/sub-frame as lever to remove/install springs.
- lifting and leaving car raised from the differential for long periods of time
- Road hazards, like big potholes, hitting a curb, etc.
- Defective bolts (very unlikely IMO).

Defective bolts are a possibility, but I could bet cash money there were at least one of the other factors mentioned above in each of those cases. But again, we'll never know here (unfortunately) for fear of self-incrimination. Checking one of the severed bolts would quickly put prove that theory or put it to rest. If defective, it'd be an immediate recall, and it's something quite cheap to fix, so I don't see BMW playing games with that.

I wouldn't consider this car unsafe Rac3rX. If you believe everything on the internet, you'd be paranoid by now . Enjoy your car man. If you don't abuse your car, there's nothing to worry about IMO. Yes, I'll keep an eye on these threads, but am not concerned about this at all since I never abuse my car, and always drive it mostly alone. Good day.
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      08-22-2011, 05:39 PM   #21
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I'm with elp_ jc. Thanks
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      08-22-2011, 05:55 PM   #22
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Using the diff as a jack point should not cause this as some others have said...
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