 Multiple investigations pointed to issues with the locomotive's trucks, the weight of the water and steam generators used for train heating, or the harmonic vibration of baggage cars behind the locomotive.In 1977 Amtrak decided to move on from the SDP40F in favor of the EMD F40PH, which was already in use on short-distance routes.Amtrak traded most of its fleet into EMD; the components were incorporated into new F40PHs.