Having read this thread, wanted to table a set of points/questions to clarify (in my mind at least) the overall picture on chassis cracks:
Many early M3Ws (inc our very early 2012 model) suffered the “torsional chassis longitudinal cracks
For these early cars this type of cracking was either fixed by a replacement chassis with improved bracing (our experience) or prevented by means of a bolt-in brace.
All more recent cars have the properly braced chassis
A number of cars with the bolt in brace seem to have suffered cracking to the wishbone mount. This has been fixed by welding in an extended web per the second picture in Rog G’s post.
As far as I am aware these wishbone mount cracks have only occurred in cars with the bolt-in brace. Is this the case??
A hypothesis from this would be that the flexing that was fixed by the bolt-in brace set up the potential for the wishbone mount cracks that then show up later. This would link to the recent MMC recall including a chassis inspection being focused on early cars.
Seeing this tread, I went to look at our wishbone mounts on our replacement braced chassis – no cracks but the wishbone mount does not have an extended web.
This for me raises a question as to whether the current production chassis has the extended web or whether this is genuinely not required because the proper bracing renders it unnecessary.
I think it important that the M3W community has a comprehensive understanding of the incidence of chassis cracking in the various versions of the car in order that robust engagement can be maintained with MMC on the topic esp as many of our cars are now accumulating significant years and miles.
