Abstract: An automatic locking mechanism is provided for latching the swingable "B" deck of an auto-rack railway car in either an upper raised position or a lower horizontal position. A spring biased plunger or bolt is normally positioned in locking engagement with a depending striker plate on the end of the swingable deck portion and may be withdrawn by the operator and rotated to a release position in which it is held out of engagement with the striker plate to permit the deck portion to be raised to its upper position. As the deck portion is raised a lug on the striker plate engages a transversely extending rotator pin on the end of the plunger and rotates the plunger away from its release position so that the plunger is automatically returned to a locking position beneath the bottom edge of the striker plate when the "B" deck portion is moved to its raised position.To return the deck portion to a horizontal position, the plunger is withdrawn by the operator and rotated to the release position.