In the attached motion study, if you run it with the sprin suppessed, the vertical bar (vBar) moves down 5mm as it should. When you unsuppress the spring, it should move the hPlate down with it since they're now connected with a spring and the hPlate has no vertical constraints.
Instead, however, the vBar moves much more than the 5mm it is supposed to move and the hPlate doesn't move at all. The spring should act as a simple extension spring (i.e., the vBar should drag the hPlate down along behind the vBar).
What am I doing wrong?