For a long while automakers focused --almost exclusively-- on vehicle weight; seeking materials, alloys, fibers and composites; just about anything that might reduce the overall weight even if only by a few pounds.

But now they're locked in on transmissions and the potential advanced transmissions represent in conserving fuel. Rivals General Motors and Ford announced their agreement to cooperate on multispeed transmissions that boost fuel efficiency.

According to the Detroit Free Press, the goal is to engineer the next generation of this expensive technology, on which Chrysler has already beaten them.

They expect to develop nine-speed transmissions for front-wheel-drive cars and crossovers and 10-speed transmissions for rear-drive trucks. The work will yield millions of transmissions for vehicles around the world.

The work will proceed in Dearborn and Pontiac. The proximity will enable engineers to meet as necessary.

Transmissions are elaborate, expensive and necessary, but sharing the basic design does not hurt the DNA of any given brand, GM spokesman Dan Flores said.

Each automaker will take the shared technology and further tune each transmission for the size and type of vehicle that will use it, Ford spokesman Mark Schirmer said.

Alisa Priddle reports that production will be done in each company's plants, using common parts to further reduce cost.

"The goal is to keep hardware identical in the Ford and GM transmissions," said Craig Renneker, Ford's chief transmission engineer. "However, we will each use our own control software to ensure that each transmission is carefully matched to the individual, brand-specific vehicle DNA for each company."

It could be three years before the first vehicles with the transmissions are on the market.

They are expected to improve fuel efficiency by 5 percent from the powertrains they replace. Automakers are working to meet new regulations in 2016 that require their new vehicle fleets to average 35.5 miles per gallon, compared with about 27.3 m.p.g. now. That requirement climbs to 54.5 mpg in 2025.

GM and Ford hope to trump Chrysler, which is introducing eight- and nine-speed transmissions -- but Chrysler has a significant head start.

Nonetheless, Ford and GM have already worked together on six-speed transmissions. That collaboration yielded more than 8 million transmissions globally. "We've already proven that Ford and GM transmission engineers work extremely well together," said Joe Bakaj, Ford's head of powertrain engineering.

And all of the experts agree: when it comes to transmissions economies of scale are critical to success.