Unity Realistic Suspension Problem!

Hi. I want to create a Buggy game with some "realistic" driving system, but i have problem with suspension.

Here is the project:

I want to create the red circles stay in same place, but wheels and opposite part of suspension go up and down. My problem is in the red circles. It doesn't want to stay in one place and suspension not working properly. I'm using configurable joints, because other joints don't give the desired effect. Sorry for bad english. Help me fast :)