What was the primary motivation behind the revolutions that took place in central and eastern europe in 1848?

Picking a primary motivation, I'd say liberalism was the leading factor in the 1848 revolutions.  There was a growing tide of liberalism, which emphasized the liberty of individuals and thus desired to reform governments in the direction of more republican and constitutional forms.  This was in opposition to the dominant conservatism of the 19th century, which valued maintaining (conserving) the old institutions of monarchy and aristocracy.  

A second factor involved in a number of the revolutions was nationalism, a desire for people of like culture and language and background to be joined together in one society.  

As a case in point, the 1848 revolution that occurred in the German states had both a liberal aspect to it (driven by university students and professors), as well as a nationalist aspect, wanting to unite the various German kingdoms and principalities into a cohesive German state.

The revolutions of 1848 for the most part did not achieve their goals, but they did sow the seeds for later changes that would come.