How to create mechanism with multiple pivot points

aparsley

I'm trying to create a mechanism with a pneumatic actuator. The actuator will extend (J2),which will rotate the "clamp" (J3/J4) (holding the workpiece). The clamp pivots on the actuator (J3), and also on the base (J4) (baselink). The actuator is also free to pivot at its base (J1). I have tried creating a mechanism, but keeps saying "unable", even though I have all green check marks.

Here is an image of the intent, and also a .step file that contains the CAD models.

Any help would be great. Thanks!