Wiktionary
crack onto
vb. (context UK Australian transitive English) To flirt with; to approach and speak to (someone), seeking romance, love, sex, etc.
Usage examples of "crack onto".
Near the top the jutting stones that he used for handholds were wide apart and he had to claw and boost himself, but then the climbing got better again until shortly he was out of the crack onto level stone.
Then the skull teetered on the tips of his fingers for an instant and tumbled with a soft crack onto the trunk of the car, rolling into the dust of the shoulder.
I heard his head crack onto the cube and he felt like a sack of dirt, lifeless, but heavy as the world.