Alco’s long history of locomotive production ended with the Century 636 of 1967-68; by this point the company was well behind its EMD and GE competitors, and early traction motor blower failures of a demonstrator C636 during trials helped put an end to any hope of remaining in the market. The C636 was a 251E-powered outgrowth of the C630, rated at 3,600hp.
Domestically, only IC, SP&S, and Penn Central bought 636s, with Alco production totaling 34 units. After Alco left the market, A.E. Goodwin turned out an additional 29 locomotives for Australian customers. In Canada, MLW continued production for a time as the M636 with Dofasco trucks for CN, CP, Cartier, and Ferrocaril del Pacifico in Mexico.
The SP&S 636s were inherited by successor Burlington Northern and retired by 1980, and similar fates befell the ICG (ex IC) and Conrail (ex PC) units.