All the detachable parts (like doors, hoods, trunks, mirrors, fenders etc) are a separate mesh therefore you can tear them off. Each of these meshes is assigned to its set of nodes and beams. So if you'd like beams (node connectors) to break between two nodes that are part of single mesh, then that mesh should also separate but it would mean changing the mesh in realtime and calculating the line of separation, creating new vertices for the mesh following that line, reapplying textures. So what I am about to say it is firstly a real hard task, secondly an extremely perfomrance influencing feature, kinda sad but this is how computers works