Dimensions not working?

I have been trying to create an animation of an assembly with about 30 parts. I was trying to use the dimensions to adjust the position of the parts and it just doesn't move at all. I switched to a simple assembly with only 2 parts, one dimension change - no difference. Is there something I am missing? To change the dimension I expand the part that I want to move, find the distance mate, double-click on the diamond, set the new distance. Re-run the animation - nothing. What am I doing wrong?

SolidworksMotion Studies