Missing Rear Sway bar Bolt

ncnmra · 09-14-2015, 08:09 PM

I've been chasing this random "pop" sound for the past year. Every time I would turn right into my driveway (and seemingly only MY driveway), I'd hear this metallic "pop" sound. I looked around the forums and saw many references to the front strut tower bars, but I had re-torqued them when I originally got the car (PS: that fixed the rattling!)

Anyhow, I came across a post suggesting the rear sway bars, and BAM!, it looks like there was a bolt missing on the passenger side:

I didn't have a direct replacement, but used the M8x25 (10.9) hex bolts that I bought with the hopes of replacing my engine mounts (never got around to it).

Anyone see any problem with this? The new bolts are longer (original Allen key type are M8x16 as per real OEM part #4), but I think there is lots of clearance behind the bracket:
http://www.realoem.com/bmw/showparts...37&hg=33&fg=45

After a few driveway tests, it appears to be fixed.

chickdr · 09-14-2015, 08:56 PM

If it fits can't see why it would be a problem. Interesting that yours is a roadster with the issue as the missing rear sway bar bolt usually plagues the M coupe and not the roadster. I would go ahead and check your engine mount bolts as mine were quite loose when checked and swapped to the bolts you have..

ncnmra · 09-15-2015, 09:00 AM

Your comment on roadster vs coupe is interesting. Why should there be any difference, don't they share most of the same parts?

I'd love to get the engine mount bolts replaced, but it seems like a job outside my comfort level, and I haven't had the opportunity or impetus to get it to a shop. What are the symptoms and/or worst case if these come out? Do they all come out at once, or just loosen?

pokeybritches · 09-15-2015, 09:17 AM

Some bolts are coated to prevent corrosion. I'd expect the engine mount bolts to be coated, so you should be fine there.

The risk with the bolts loosening is that they can fatigue over time, and eventually shear.

chickdr · 09-15-2015, 09:17 AM

I am not sure why the coupe has the sway mount bolt problem so much more often but I think yours is only the first or second time I have heard of it.
Try this thread for more info: http://www.bimmerfest.com/forums/sho...d.php?t=296152

This also goes for the engine bolts(typically a coupe issue, but was present on my roadster). The engine mount bolts were improperly torqued at the factory from what I understand. The symptoms can be a pain as what happens if they back out is the engine collapses on the passenger side when the bolts shear. The car still drives, but of course you hear strange sounds as the engine moves around. I didn't get to that point but most of my bolts were able to be removed without a wrench if that gives you any idea.

Here is great thread on the engine mount bolts.

http://www.bimmerfest.com/forums/sho...ht=motor+mount

09-14-2015, 08:09 PM	#1
ncnmra Second Lieutenant 39 Rep 269 Posts Drives: 2006 M Roadster Join Date: Jul 2012 Location: Canada iTrader: (0)	Missing Rear Sway bar Bolt I've been chasing this random "pop" sound for the past year. Every time I would turn right into my driveway (and seemingly only MY driveway), I'd hear this metallic "pop" sound. I looked around the forums and saw many references to the front strut tower bars, but I had re-torqued them when I originally got the car (PS: that fixed the rattling!) Anyhow, I came across a post suggesting the rear sway bars, and BAM!, it looks like there was a bolt missing on the passenger side: I didn't have a direct replacement, but used the M8x25 (10.9) hex bolts that I bought with the hopes of replacing my engine mounts (never got around to it). Anyone see any problem with this? The new bolts are longer (original Allen key type are M8x16 as per real OEM part #4), but I think there is lots of clearance behind the bracket: http://www.realoem.com/bmw/showparts...37&hg=33&fg=45 After a few driveway tests, it appears to be fixed.
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09-14-2015, 08:56 PM	#2
chickdr Lieutenant Colonel 140 Rep 1,989 Posts Drives: 2006 M Roadster Join Date: May 2009 Location: Buford, GA iTrader: (0)	If it fits can't see why it would be a problem. Interesting that yours is a roadster with the issue as the missing rear sway bar bolt usually plagues the M coupe and not the roadster. I would go ahead and check your engine mount bolts as mine were quite loose when checked and swapped to the bolts you have..
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09-15-2015, 09:00 AM	#3
ncnmra Second Lieutenant 39 Rep 269 Posts Drives: 2006 M Roadster Join Date: Jul 2012 Location: Canada iTrader: (0)	Your comment on roadster vs coupe is interesting. Why should there be any difference, don't they share most of the same parts? I'd love to get the engine mount bolts replaced, but it seems like a job outside my comfort level, and I haven't had the opportunity or impetus to get it to a shop. What are the symptoms and/or worst case if these come out? Do they all come out at once, or just loosen?
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09-15-2015, 09:17 AM	#4
pokeybritches Colonel 479 Rep 2,782 Posts Drives: ESS/G-Power Z4M, VF Z4, 996tt Join Date: Sep 2009 Location: Los Angeles iTrader: (12) Garage List 2006 BMW Z4M [10.00] 2006 BMW Z4M [8.50] 2003 BMW Z4 3.0i [9.00]	Some bolts are coated to prevent corrosion. I'd expect the engine mount bolts to be coated, so you should be fine there. The risk with the bolts loosening is that they can fatigue over time, and eventually shear. __________________ VF Engineering Z4 3.0i, ESS Z4M, G-Power Z4M, 996 Turbo
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09-15-2015, 09:17 AM	#5
chickdr Lieutenant Colonel 140 Rep 1,989 Posts Drives: 2006 M Roadster Join Date: May 2009 Location: Buford, GA iTrader: (0)	I am not sure why the coupe has the sway mount bolt problem so much more often but I think yours is only the first or second time I have heard of it. Try this thread for more info: http://www.bimmerfest.com/forums/sho...d.php?t=296152 This also goes for the engine bolts(typically a coupe issue, but was present on my roadster). The engine mount bolts were improperly torqued at the factory from what I understand. The symptoms can be a pain as what happens if they back out is the engine collapses on the passenger side when the bolts shear. The car still drives, but of course you hear strange sounds as the engine moves around. I didn't get to that point but most of my bolts were able to be removed without a wrench if that gives you any idea. Here is great thread on the engine mount bolts. http://www.bimmerfest.com/forums/sho...ht=motor+mount Last edited by chickdr; 09-15-2015 at 09:23 AM..
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