The TH400 is an automatic shift, three-speed, longitudinally positioned transmission. It is widely regarded to be a supremely durable and legendary transmission.
The Turbo 400 was introduced in 1964 in Buick and Cadillac cars and in Chevrolet and Oldsmobile cars the following year. An innovative variable pitch stator was available in the 1965-1967 cars that could essentially vary the characteristics of the torque converter.
The TH400 made its way into heavier-duty GM trucks in the 1970s in 2wd and 4wd configurations. The 400 was not just a GM-exclusive transmission. It is an immensely popular transmission in the automotive industry as well as the aftermarket. They are found in GMs, Jeeps, Jaguars, Rolls-Royces, Ferraris, and others.
As with other GM transmissions, GM changed the naming scheme of the TH400 in 1990 and it was then referred to as the 3L80 (3-speeds, Longitudinally positioned, 8000 lbs. GVW). An overdrive version of it was introduced as the 4L80-E. This electronically controlled transmission remains in production and wide use in heavy-duty GM and military applications.