GM and Ford have formed a new alliance to develop a high-mileage 10-speed.

General Motors and Ford Motor Co. have formed an unusual alliance designed to help them meet increasing stringent fuel-economy standards by jointly development a new 10-speed automatic transmission.

The announcement underscores the increasingly difficult challenges manufacturers face as they shoot for a 54.5 mile-per-gallon mandate set to take effect in 2025.  That has led a growing number of automakers to set aside traditional rivalries and form potentially far-reaching alliances aimed at development new engines, transmissions, even entire vehicles that can be shared among various brands.

The new gearbox envisioned by GM and Ford will be utilized on a variety of different front- and rear-wheel-drive products, the makers said, noting their shared goal of bringing the technology to market sooner, and at a lower cost, than if they worked together.

“Engineering teams from GM and Ford have already started initial design work on these new transmissions,” said Jim Lanzon, GM vice president of global transmission engineering.

While Lanzon did not outline specific mileage gains targeted by the project, he said, “We expect these new transmissions to raise the standard of technology, performance and quality for our customers while helping drive fuel economy improvements into both companies’ future product portfolios.”

Advanced transmissions have become a critical technology in the industry’s push to increase mileage while also reducing vehicle emissions. A growing number of automakers have migrated to six, seven and even eight-speed gearboxes, and both Chrysler and Land Rover recently confirmed plans to introduce 9-speed transmissions on various models.

Those makers will use a design developed by German supplier ZF whose CEO Stefan Sommer estimated they could reduce fuel consumption by “nearly 13%” compared to older-style 6-speeds.

The GM/Ford project would take the gear count up to 10, which many automotive engineers believe is about the maximum before mass, inertia and friction – as well as cost – would overcome any potential advantage.

Indeed, even at seven and eight speeds, transmissions have to be carefully designed to prevent constant “hunting” as an automatic gearbox switches from gear to gear, something studies reveal can disrupt customer comfort.

As a result, the physical design of the transmission itself becomes only part of the development process. Making the new GM/Ford 10-speed live up to expectations will require extensive work on the software that controls the gearbox. Notably, while Ford’s transmission chief Craig Rennecker says the two makers will develop common parts and components, they will develop their own software – which could run into the 100s of thousands of lines of code.

For decades, domestic automakers were barred by law from cooperating with one another, but such restrictions have been eased in recent years to reflect the increasing challenges the industry faces, especially for makers hoping to go it alone.

The new 10-speed will become the third joint project between GM and Ford. But those makers each have entered into a number of other alliances. General Motors’ European subsidiary is working closely with France’s PSA Peugeot Citroen on a variety of projects. Ford has teamed up with such erstwhile rivals as Toyota, Nissan and Daimler AG on other projects including the development of advanced powertrains.

“It’s partner or die,” contends David Cole, president-emeritus of the Center for Automotive Research, who believes that alliances, whether large or small, will become the norm in the auto industry in the years ahead.