In accordance with the present invention a lock block link 34 has a first end 36 connected to a trailer hitch bumper block 22 and a second end 40 which engages a lock block 46 which holds the hitch jaws 16 in closed position. The lock block link 34 is supported by an operating shaft link 54 extending from a manual operating shaft 50 extending to the side of the hitch. When the bumper block 22 is engaged by a tractor, the bumper block rotates about pins 30 connecting the bumper block to the hitch head 10. This rotation moves the lock block link 34 and in turn the lock block 46 rearwardly, which allows the jaws 16 to rotate to open position to allow exit of the trailer king pin. A lost motion connection 31 is provided in the connection between the first end of the lock block link and the bumper block to allow the lock block link 34 to move relative to the bumper block when the lock block 46 is moved rearwardly manually by the operating shaft. This connection may comprise at least one elongated slot 32 in the bumper block into which fits the first end of the lock block link.