To people NEW to the M30, this is something they are finding out. This topic is archived here (http://forums.f31club.com/viewtopic.php?f=1&t=1355)
In 2006, Edrik (Nightmoves) called me up and said there are cracks on the chassis when he opened his door. I went and looked at my M30 and saw them. To double check, Edrik called someone else and I called 2 other people.
On my end, 1 was verified to have a crack and the other didn’t
We posted this on f31club’s forums and everyone went out and looked. All of the Convertible guys said they didn’t have it, while most of the coupe owners verified they did have the cracks, some on both sides.
What we learned was the convertibles have had added bracing since there are no B or C pillars, they were more rigid and stronger than the couple.
We also concluded that since the coupes were modified, it was making the M30 heavier. This was to meet the US’s National Highway Traffic Safety Administration (NHTSA) safety standard.
With the M30 being heavier, we assume the reinforcement is in certain areas, such as the doors or the front and rear of the car. There might not be as much or enough support in the middle, making it a weak point. The M30 is also a long car and that could also be a factor. so we have to assume that once the door position is open, the bracing for the chassis isn’t as strong. This might also be part of the door sag problem in a sense that the middle might not be aligned with the door.
So what does it look like? Here I am pointing to where my crack was located and welded up. For comparison, Ben took this same picture and marked where his cracks were in green.
Jesse took pictures of both sides of his car.
Even though we see these cracks in various stages, I have yet to see a car sudden ripped in half because of this.
So how do people fix this issue? What I’ve seen people do is drill out the ends of each crack (to stop from spreading) and get it welded up. I only know of one person who actually got a R31 floor bar and used it for extra bracing. Another solution that has been tossed out there is getting some of the convertible reinforcements and weld them in (there are a couple that reinforce this section on the convertible). Again, I have yet to see anyone do this.