These units have been retro-fitted with air brakes, in addition to the original vacuum brakes. The WDM-7 locos have a maximum speed of 105 km/h (65 mph),[2] restricted to 100 km/h (62 mph) when run long hood forward - the gear ratio is 94:17.
Fifteen of these locomotives (road numbers #11001 to #11015) were built from 1987 to 1989 as a low-powered, “lightweight” version of the original ALCO. Like the WDM-6, the IR wanted a lower powered locomotive to handle small rake local and passenger services. However, all sheds declined them and they ended up at Ernakulam where they were used to handle local and shuttle services with good degrees of efficiency. Becoming aware of their abilities, the Southern Railway moved all the WDM-7s out of Ernakulam to Tondiarpet, where they are housed there as of 2023. These days,[when?] they are seen being used as shunters at Chennai Central or for light passenger haulage. One (#11008) has been modified[when?] to run on bio-diesel.
These Co-Co diesel-electric locomotives were designed primarily for branch-line duties (top speed 105 km/h). They have two 3-axle bogies. The power-pack is a 12-cylinder Alco 251B unit. They are a lower-powered variant of the WDM-2 (the latter produces 2600 hp of usable power, as opposed to the WDM-7 which produces 2000 hp). They were formerly housed at Erode and Ernakulam as well. They are reliable and rugged locomotives even though low-powered. They can be easily recognised by the lack of grilles on the short hood; in fact, they look exactly the same as the WDM-2 except for the “clean” short-hood-forward nose without grilles. Two locos currently[when?] operate on a mixture of bio-diesel and diesel. As of March 2024, 14 of the 15 locomotives built are still in service.
