Large numbers of the NER G6 0-4-4WT class were made redundant during the 1890s. Forty of these were rebuilt as 0-6-0T shunting locomotives at York Works between 1899 and 1904. Ten further were rebuilt at Darlington, in 1907-8 and a further ten in 1921.
The G6 BTP were built with Westinghouse brakes. These were replaced with steam brakes on all but two of the J77s (Nos. 37 and 1437). These were removed in the late 1930s. Twelve of the J77s received vacuum brakes after 1945. This fitting was usually accompanied by the addition of carriage heating equipment.