A differential lock mechanism is provided for use in an axle assembly having a differential, an input member and first and second axles. A lock sleeve is co-axially disposed about the first axle, with the lock sleeve being rotatable with the first axle and laterally movable relative to the first axle. A lock collar is co-axially disposed about the lock sleeve and is laterally movable between outboard and inboard positions. A biasing member biases the lock sleeve toward the rotatable carrier and a lock fork is engaged with the lock collar. The lock fork is operable for moving the lock collar between the outboard and inboard positions. The lock collar is disengaged with the rotatable carrier when the lock collar is in the outboard position and is engaged with both the rotatable carrier and the lock sleeve when the lock collar is in the inboard position.