Abstract: Method of converting a hopper type of rail car to accept a wider outlet gate permits existing cars which are in over-supply to be made useful. The method requires that the opposed pairs of side slope sheets of the original car, and the opposed pairs of center and end slope sheets which are joined to them to form the bottom portions of the hoppers, be cut apart. One of the pairs of slope sheets then has its width reduced at its lower end portion while the lower end portions of the other pair of slope sheets are cut away and replaced by new slope sheet portions which are of greater width than the original portions. After the mounting flanges for the original outlet gates are removed, new mounting flanges which are wider in one direction and narrower in the other, are located in a predetermined fixed position relative to the frame of the car, preferably by an assembly jig which is temporarily clamped to the car frame.