Box collider in hierarchy in pivot point problems

Hi, I made picture which describes a little my problem, I think it will be understandable enough.


http://imagizer.imageshack.us/v2/800x600q90/546/126b.png

 

I was trying to do this with spring joint and it started to work as I wanted but block was going through wall when I was too near.
The same with limited joint, can't get this to work