CSX had begun overhauling SD70AC that have been stored for several years in order to return them to revenue service.
The work is being done at the locomotive shop in Huntington, West Virginia, and involves 25 units.
Trains magazine reported that the work includes replacing the original Siemens control system with a new Mitsubishi MELCO control system.
CSX officials hope that the new components will enhance the performance of the SD70AC locomotives. They described the work as more an upgrade than a rebuild.
The first rebuilt unit could hit the road in early September.
Other work being done includes rebuilding the EMD 710 prime movers by giving them a refurbished engine block and all new components.
The locomotive cabs are receiving new floors and ceilings, LED lighting and new display screens. An electric refrigerator has been installed in the cabs.
A new CCB2 airbrake system is being installed and the trucks are also being rebuilt or replaced with new wheel sets being added.
A CSX supervisor told the magazine that some of the newer components on the locomotives will be easier to service and replace.
He said that tests have found that a rebuilt unit has a smoother ride and better transference of power from the engine to the wheel.
The big difference between the old and the new has been that the throttle response time in the rebuilt units is better, saying “you don’t get that jumpiness and hesitation.”
The rebuilding process is taking about six weeks to complete.
CSX expects work on 15 SD70ACs to be finished by the end of this year. The remaining 10 will be completed in 2020.
The rebuilt units will carry a special decal to distinguish them from those locomotives not included in the program.
CSX has 200 SD70ACs in the 4500 and 47700-4030 series that were built between 1997 and 2006.
The 25 units being overhauled in Huntington are in the 4500 series.