 Although VR did not publicly indicate the T was intended to replace the J class, it proved to be such a successful design that further orders of this locomotive class were made during the late 1950s and 1960s, gradually displacing the J class from many of its normal duties.Together with the K and N classes, the J class had its boiler pressure raised in the early 1960s from , which raised their nominal tractive effort to .Locomotive J 546 was selected for installation of a Laidlaw Drew oil firing system in place of the convention weir-type burner following recommendations from the 1957 Australian and New Zealand Railway Conference.