to the basic Rzeppa constant velocity joint and was rewarded in the 1960s when much of the world's motor industry switched to front wheel drive using Birfield joints, the CV joints now made by GKN Driveline and currently installed in more than one-third of all new cars worldwide. Notable improvements to the original Rzeppa design have been the elimination of the need for a splined coupling and Birfield's modifications to the ball grooves and their track-steered ball cage introduced with BMC's Minis in 1959. Rear axles Salisbury Axle in USA was also part of the Spicer Group and in 1939 the Salisbury Transmission Company was formed in Britain to manufacture hypoid rear axles and, in the late 1950s, Powr-Lok limited-slip differentials. Automotive clutches Laycock's principal product became spring diaphragm clutches. From the late 1940s into the 1970s it made under de Normanville patents an add-on epicyclic overdrive unit which saved manufacturers from incorporating a 4th or 5th gear within their gearboxes. Birfield multinational group 1964 Group members included Hardy Spicer; Laycock Engineering; Forgings & Presswork; Salisbury Transmission; Kent Alloys; Bound Brook; Felco Hoists; Hardy Spicer Walterscheid; John C Carlson; T B Ford; Shotton Bros; Felco Hoists; Birfield Filtration; R Jones & Co; Oddy Engineering; Birfield Machine Tools; Birfield Extrusions; Foundry Mechanisations (Baillot); A E Callaghan & Son; Micron Sprayers; Birfield Industries. Overseas group members Bound Brook Bearing Corporation of America, Nordiska Kardan AB; Birfield (Ireland); Birfield (Nederland) Tranmissie; Felco France. Overseas interests 37.5 per cent of Uni-Cardan AG, 21 per cent of France's Glaenzer-Spicer SA in any case controlled by Uni-Cardan, Birfield Transmissioni SpA in Italy jointly owned with Glaenzer-Spicer, an association with Toyo Bearing of Japan and lesser interests in businesses in many other industrialised countries. GKN Driveline In 1966 Guest Keen & Nettlefold seeing advantage in amalgamating with its local competition and wanting to pre-empt an expected bid from USA's TRW Inc. bought Birfield the sole UK supplier of CVJs. There were also particular significant advantages in the amalgamation such as Hardy Spicer's strength in the EU and USA whereas GKN was weak in both those parts of the world. As GKN Driveline its constant velocity joints take near 50 per cent of the world market and Driveline employs about 22,000 people at 46 locations across 23 countries. References External links CVJ Mechanisms (engineering)