The C30-7 and C36-7 were upgraded variants of the “Universal Series” models U30C and U36C, originally with the same power output. The C30-7 still had the 16-cylinder 7FDL-16 engine, producing 3,000 hp. 1,087 were built between 1976 and 1986, of which 305 went to Mexico and two to Mongolia. The largest customers in the US were Burlington Northern with 242, ATSF with 157 and Union Pacific with 140. In 1984, Conrail received 50 C30-7A which had a twelve-cylinder variant of the engine, still producing the same power, but at a lower fuel consumption.

602 C36-7 were built with either 3,600 or 3,750 hp between 1978 and 1989. From these, the largest part was sold to China Railway which used 422 and designated them ND5. GE do Brazil built 15 which went to NdeM in Mexico. In Australia, A Goninan & Co. (today UGL Rail) built three for Hamersley Iron. The largest North American customer was Missouri Pacific with 60.