The invention relates to a lower shift mechanism for the rigid covers (10) of a railway freight wagon, the covers in their closed positions (K) closing the wagon space (50) and in the open positions (A) being movable over the covers in the closed position in the longitudinal direction of the wagon. The lower shift mechanism comprises transport rollers (3) in the covers, stationary run rails (2) in the wagon frame (100), and pivot axles (4) that can be moved around the centre lines (14), which are in the longitudinal direction of the wagon, the axles having, next to the openings (20) of the run rails, lifting rail sections (6) fixed by means of first arms (5a), and an auxiliary rail section (7) fixed by second arms (5b). The covers are positioned by lifting and lowering them by the transport rollers in the transverse direction of the wagon into their closed positions (K) and their open positions (A), whereby the transport rollers roll on the run rails and on the auxiliary rail sections that are in the said openings. The pivot axles pivot (R) so that the lifting rail sections in the opening movement (K-A) of the cover first move mainly outwards from the wagon space and then also upwards from below into the openings (20) of the run rails and in the closing movement (A-K), in opposite directions, while in the opening movement of the cover, the auxiliary rail sections move away from the openings of the run rails and, in the closing movement, down back into the openings (20). IMAGE
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