Answer is presented as a set of links to tutorials (on AR-CAD Blog). In all the below tutorials, models from GrabCAD were imported inside SpaceClaim and assembly constraints/conditions were defined between the components/parts. Later, motion simulation was performed using SC-Motion.
1) External Gears Assembly and Simulation in SpaceClaim
2) Internal Gears Assembly and Simulation in SpaceClaim
3) Rack and Pinion Assembly and Simulation in SpaceClaim
4) Worm Gear Assembly and Simulation in SpaceClaim
5) Bevel Gears Assembly and Simulation in SpaceClaim
6) Assembly of Vertical Engine in SpaceClaim and its Simulation
SC-Motion is a motion and dynamic simulation addin for SpaceClaim. SC-Motion 2012 (version) is available for 99 USD. For more details, please visit http://www.ar-cad.com/sc-motion/index.html