 The fleet was subdivided into 5000, 5050, and 5070 series types.The first 12 former 7800 series cars were rebuilt between November 1978 and August 1979, reformed as two four-car 5000 series sets and two two-car 5500 series sets.These sets were initially not air-conditioned, and used the ventilators and motor generators removed from 8000 series sets that had been refurbished with air-conditioning.