dynamic block assistance if anyone is bored!

[ColinPearson]

happy friday y'all.  I feel pretty dumb on this one, but I just can't figure it out.  I've tried a bunch of stuff with parameters/actions and I'm not getting there.  Then I tried with Geometric Constraints and things go haywire.  Tried again with Dimensional Constraints and I just end up changing geometry that I don't intend to.

 

All I want to do is use a Stretch to move the deck of this trailer up/down vertically and have the red linkage pivot.  Default (lowest height) is on the left and max height is shown on the right.  In the max height one I've got the linkage drawn how I want it to pivot.  In real life, this trailer goes up/down on an arc, but for planning purposes with this block, I don't need or want it to move that way, so I'm using the straight vertical motion.  The linkage is basically in there for looks and that's all it's needed for.  That's all to say that the exact angle of the thing is really important for this.  

 

I don't expect anyone to do this necessarily, but I know a lot of times people like tinkering.  Thank you very much if you feel like it, or just feel like taking a peek.  I either get the red piece to rotate but it's wonky, or no rotation at all.  

 

THANK Y'ALL.  HAVE A GREAT WEEKEND.

 

SMPT test.dwg