Design Table in an Assembly

Hello,

I am currently having a little problem with creating a design table once i am in an assembly. I would like to know if there is a quick fix or if what i am trying to accomplish is possible. What I am trying to do is just have 3 parts, 1 fixed, the other 2 mated so they can move in 1 direction, than add a dimension for their position. I would like to do this with a separate excel sheet (Design Table)

The problem I am having is once I assemble everything, add the dimension, open the design table,then change dimensions. nothing happens. Any tips, tricks or links would be appreciated.

Thank you.

SolidworksConfigurations design Tables