Maya, modelling a car, problem with converting to SubD

Hi,
I'm modelling a car. Now i have split the car into several parts, duplicated the surfaces and assigned them to layers. But after converting such parts to SubD , like e.g. the front bumper, maya converted each surface itself. After that my front bumper consisted of many rounded surfaces, having no contact to each other. Could anybody tell me where's the mistake. Thanks for any response!

Picture:

https://www.3dm-mc.com/forum/showthre...6783#post16783