The 700R4 is a 4 speed automatic transmission, with a 30% overdrive in 4th gear. This transmission was produced by General Motors. The development of this transmission was primarily targeted to improve fuel economy, and this was accomplished by a number of modifications, not the least of which was the 30% overdrive capability.
The 700R4 was used widely on rear-wheel drive car and truck platforms. The 700R4 is a good choice if looking to convert and older 3spd to an overdrive transmission.