 The SD40 was succeeded by an upgraded Dash 2 version called the SD40-2.After having been succeeded by the more modern SD40-2, a large number of SD40 have been upgraded with more modern equipment.The main difference between rebuilt SD40 and genuine SD40-2 is that the latter use a longer frame and has longer front and rear porches, while the rebuilt SD40 have a shorter frame 

A common product of rebuilding SD40s, and sometimes SD40-2s, is an SD40-3.