I came across this article last summer when I was researching the issue:
BMW TO USE NEW GM TRANSMISSION FAMILY
FOR RELEASE: Sept. 18, 1996
CONTACT: Joseph C. Lawrence
Phone: (810)857-4029
PONTIAC, Mich. -- General Motors Corporation’s GM Powertrain Group announced today it has signed a multi-year agreement with BMW AG to supply BMW with the all-new Hydra-matic 5L40-E five-speed and 4L40-E four-speed automatic transmissions for a wide range of future BMW vehicle applications.
GM has supplied Hydra-matic automatic transmissions to BMW since 1991. Currently, the Hydra-matic 4L30-E is used in BMW’s 3- and 5- series cars and the Z3 roadster. GM Powertrain’s Strasbourg, France plant builds the Hydra-matic 4L30-E and will produce the new 5L40-E and 4L40-E, as well.
"We are pleased to be able to continue our association with BMW and are looking forward to working with its product development experts to successfully integrate these two new transmissions into BMW’s product lineup," said William J. Boskey, director, International Sales, Marketing, and Joint Ventures for GM Powertrain.
The Hydra-matic 5L40-E and 4L40-E automatic transmissions were introduced at the 1995 Internationale Automobil-Ausstellung (IAA) in Frankfurt. The two transmissions, with a maximum engine torque of approximately 380 Nm, can be used in passenger car or light truck applications, for either rear-wheel or all-wheel drive configurations. Advanced electronic controls and light weight ensure excellent fuel economy.
The Hydra-matic 5L40-E is GM’s first five-speed automatic transmission. The five speeds provide improvements in performance, ability to climb grades, fuel efficiency, lower emissions, and lower noise levels at cruising speeds. Both the 5L40-E and 4L40-E offer GM Powertrain’s new Electronically Controlled Capacity Clutch in the torque converter for improved fuel efficiency and shift smoothness, along with “fill-for-life” transmission fluid for ease of maintenance.
GM Powertrain is the world’s largest manufacturer of engines, automatic transmissions, castings and related components. Based in Pontiac, Michigan, USA, the GM Powertrain Group operates 27 plants and eight engineering centers in the United States, Canada, Mexico and France, and employs nearly 57,000 people. GM Powertrain has a global focus on serving customers within GM and throughout the world, from North and South America, to Europe, Asia, and Australia. Product and process teams work together to create the best powertrain products and services.
This article explains why:
http://www.findarticles.com/cf_dls/m3012/3_180/61361664/p1/article.jhtml