Green’s Dictionary of Slang

(US) an act of defecation.

1845		in N.E. Eliason Tarheel Talk (1956) 154: [A train companion was left behind] at the Warrington depot, he having gone to the tavern to take a Jim Crack.
1956		N.E. Eliason Tarheel Talk 187: For excretory functions there are two or three slang terms, such as take a Jim Crack.