I went on holiday and my Z4M stayed for 2 weeks with my M-specialist to check out the noise that was still coming from the front of the car when hitting small bumps on the street. The noise started after the fitment of the Bilstein suspension in 2014.
They now checked every bit of the front suspension and found nothing was technically wrong or damaged.... They checked if the firewall braces were tight enough. It is common knowledge that if the bolts of the firewall braces are loose they can make noise. But every bolt was correctly fixed and there was zero movement when pulling the firewall brace by hand. As a final test they removed the OEM BMW strutbrace and the firewall braces and did the same test run. The typical rattling noise was gone...! They fitted the OEM BMW strutbrace again and the noise was still gone...so back to fitting the firewall braces and yes the noise was back... I went home and I did the test myself (removing and refitting the firewall braces) and had the same result when test driving on a bumpy road!
So afters hours of testing it is finally know what makes the noise.... The strange thing is, this noise started from day 1 after the Bilstein suspension was fitted (never heard it before). So what to do now??? The firewall braces need to be fitted and so the the annoying noise is coming back.... When pulling the firewall braces, then there is zero movement! When closely investigating the firewall braces mounting point on the strut towers, then you can see some really small cracks in the mounting points under the mounting plate of the strutbrace (but nothing alarming in my opinion)... I will try to make pictures of the cracks this week (so you guys can see what I mean with small cracks). In my opinion it does not make 100% sense that these small cracks could make the firewall braces move and create the noise... If the firewall brace mounting plates would be loose (like in this case:
http://www.zpost.com/forums/showthread.php?t=298573) then it could totally explain the noise... But in my opinion is now not the case, because there is no movement in the firewall braces mounting plates. So maybe the problems is the firewall braces themselves.....but how could they create noise if they are not moving?
You can say; do a test! Order 2 now mounting points for the strut tower and get them spot welded on....do a test drive and see if the noise is gone. That not so expensive to do and sounds like something that can be done. The official BMW dealer will not do this (already checked), but my M specialist or a body repair shop can do this welding. Problem; welding on the chassis is not legal for the yearly MOT vehicle inspection
in my country...
If they notice it on the inspection then it will result in a car that will be denied road access! It's true; I know about people who had this happen after the MOT inspection spotted a small aftermarket spot welding on the chassis. This resulted is a really expensive operation to get the car back to street legal....
So then there is the option of buying the rather expensive Rogue engineering race brace (
http://www.ca-int.co.uk/variants-cGFyZW ... 0MQ==.html)
This Rogue engineering strutbrace that has some extra stiffening on the spot were the firewall braces are connected on the struts.
http://www.zpost.com/forums/showthread.php?p=12491034
But I have read that the fitment of this item is not 100% and it needs a lot of tweeking to fit correctly? 2 other downsides; for work on the engine you will always have to remove the entire strutbrace (and not only the middle part as on the OEM BMW strutbrace I have fitted now). The other downside may be that the noise is still there....and I have bought something that I did not needed and is no solution for my problem.
The OEM firewall braces are hollow, so maybe they are some sort of resonance room and create noise...? A firewall brace from strong strut is not hollow and could maybe delete the noise?
http://www.ca-int.co.uk/variants-cGFyZW ... zMjE=.html