would it actually be possible that you might get a successful northern secession?
But it would depend on what you define as north. New England and New York are distinct possibilities, but maybe even the Ohio-Valley states?
By "the North," I presume you mean Yankeedom, which is New England, New York State (but not NYC and its environs), and the Upper Midwest (including northern OH/IN/IL).
Were Yankeedom to secede, it would be incredibly hard to swing the Midlands of New Jersey and Pennsylvania and the central Midwest into the rebel fold as they had very few grievances with the Union. The Ohio Valley is itself an Appalachian stronghold, and they aren't going to pick Yankeedom when they experienced their own civil war IOTL about whether or not to support their Southern neighbors.
I think the last best chance for a "Northern secession" is Polk getting his wish in '48, that is, "All Mexico" being gobbled up by the Union. This sort of imperial overreach could deepen sectionalism and rivalry to the point where national reconciliation is out of the question, especially if we get a three-way civil war between Yankeedom, the South, and Mexican nationalists.