Spring Compression

Hello,

I am having a bit of trouble making my spring animate in an assembly. I can get to the animtation process fine but when I compress the spring by clicking and dragging one end, the whole spring kind goes a bit wonky.

Just wondered if you chaps had any advice on a mate I could use that would allow it to run in a straight line up and down. I have tried using a sketched line at the edge and mating it that way but it just doesnt seem to want to move afterwards.

Thankyou

SolidworksParts And Features