Co-Co diesel electrics originally from Alco (1961-1964), later manufactured by DLW (1968-1993). The initial batch of 55 from Alco were used for evaluation and comparison with a similar batch of General Motors locos. The Alcos were chosen as the preferred MG main-line diesel locos. Alco model is DL535A. Originally manufactured with only vacuum brakes and dynamic braking, no air brakes. Rated at 1350/1200hp. Max. speed 100km/h. YDM-4A are identical to YDM-4, except that they were supplied by MLW (1964) — the Canadian batch consisting of about 99 locos. Some of the MLW locos do not have the ‘A’ suffix in the class designation.
Ahmedabad was the main centre for these locos. A few were hauling local trains in the Secunderabad-Bodhan section in 1997, and are reported [8/00] to be working around Mysore, Villupuram, etc. Some from the Guntakal shed are still [7/02] hauling trains on the Pakala-Guntakal-Bellary route. Some are thought to be at Gandhidham after gauge conversion left Gandhidham – Palanpur an isolated MG line.
DLW has exported some (15 each) of these to Tanzania and Vietnam (1976-1985), and to Bangladesh (2000?). The ones for Bangladesh were classed YDM-4BR and had dual cabs, a change achieved without modifying the length of the loco. This variant turned out later to have major cooling problems.
Malaysian railways (KTM) acquired 39 used YDM-4’s from IR in 1996. It is not clear if they were leased or sold. Of these, 14 were returned to India by 1999. In Malaysia they retained their IR road numbers (between 6352 and 6725).
Builders: Alco, MLW, DLW
Engine: Alco 251B-6 (Alco/MLW), Alco 251D-6 (DLW); 6 cyl., 4-stroke, inline
Transmission: Electric (DC-DC, in contrast to most other locos that were AC-DC).
Axle load: 12t. Bogies: Co-Co trimount.
Fuel capacity: 3000l