From what I can see, the only way to set the passgrade for a given assignment is to go into your gradebook, select Categories and Items -> Simple View (or Full View), click the Properties icon for the assignment, and set it there. This seems needlessly complicated, especially if you have many instances of the same assignment type, which you would like to all have the same passgrade.
It seems much more sensible and much less of a pain to be able to set a default passgrade when creating the assignment, but there doesn't seem to be a way to do this. MDL-13831 makes a similar request, but seems to have been ignored for years (created 2008, last updated 2011, no comments from developers).
Am I missing something, or is this just not a big deal to anyone else? If the latter, what is your workflow like? Create assignments, then go to gradebook and navigate to the Properties page for each one to set the passgrade?