While enjoying my new (to me) Southern Pacific Trainmaster it was discovered that the caboose was emitting sparks from under the trucks. These sparks were so large that they even extended outside of the truck frames. It seems something went wrong when the rollers were riveted to the truck. The shaft that the roller is attached to extends so far up that it bumps the bottom of the metal truck frame, completing the circuit. Both trucks have the same problem. For now a bit of electrical tape is doing the job. The coil spring is very weak and I am not sure what it is supposed to do. Also, the roller is positioned directly over the rivet holding the assembly together, blocking access to it. Any ideas for a more permanent fix?