Abstract: A pull trailer dump truck assembly (10) is disclosed which uses a dump truck (12), a trailer (18) and an improved locking mechanism (24). The locking mechanism (24) includes at least one pair of cooperating locking wedges (54, 56) mounted on the trailer body (22) and the trailer frame (20) which move into wedging engagement when the trailer body is moved into the secured, traveling position on the trailer frame. A self-locking pintle hook (60) can be mounted on the frame to automatically lock with a pintle eye (58) as the wedge members move into wedging engagement to secure the trailer body (22) on the trailer frame (20). A power cylinder (66) can also be provided to move a locking wedge member (64) on the trailer frame and a locking wedge member (62) on the trailer body into locking wedged engagement.