The construction of the Jubilee line and the Heathrow extension of the Piccadilly line required yet more works trains, and eleven more locomotives were ordered in 1972, with delivery in 1973. They were built at Doncaster Works by British Rail Engineering Limited. The motors were refurbished from redundant District line stock, but the bogies were new. Although based on the standard Z-type bogie used since the 1930s, they incorporated roller bearings, rather than white metal axleboxes and suspension bearings. Three of the locomotives were built to replace the three metadyne vehicles, but those were not actually withdrawn until 1977.