Abstract: A rail car truck side frame for use in a frame brace truck which has stabilizing cross braces extending between the side frames. The side frame has a top compression member and a bottom tension member which are joined by upwardly and outwardly slanted end walls. Each side frame has a pedestal horn spaced from each end wall. There is a bracket assembly at the lower end of each wall for use in mounting a cross brace. Each bracket assembly includes a three-walled channel mounting bracket, with one wall having an opening therein for the mounting of the cross brace. There is a base plate welded to an outboard side of the side frame and having a first portion welded to an upper edge of the channel mounting bracket for providing support therefor. A second portion of the base plate is welded to the side frame pedestal horn. There is a support plate welded to an inboard side of the side frame adjacent its unit guide pocket and welded to the base plate for providing support therefor.