DETROIT – General Motors has reached a deal to sell its Allison Transmission unit for $5.6 billion to private-equity firms Carlyle Group and Onex Corp., sending the automaker’s shares to the highest level in 2 1/2 years, according to Reuters. GM had said in January that it was looking to sell Allison, which makes transmissions for commercial trucks, buses, and military vehicles, but the negotiated price was more than some Wall Street analysts had expected.

GM shares reacted by rising more than two percent, hitting their highest level since January 2005, on speculation that the automaker could use the proceeds from the Allison sale to fund a cost-cutting deal on health care in upcoming talks with the United Auto Workers union.

GM said the sale would include almost all of the Allison Transmission unit’s assets, including seven manufacturing plants in Indianapolis and the unit’s worldwide distribution network. The sale is expected to close as soon as the third quarter, GM said, provided the deal is approved by GM’s industrial union and regulators.

Shares of GM, the world’s No. 2 automaker by volume behind Toyota Motor Corp., have gained more than 29 percent this month on building expectations that the company could win sweeping changes to its contract with the UAW that would lower hourly labor costs, according to Reuters.

GM said it would retain a Baltimore, Md., plant now under Allison that makes conventional and hybrid transmissions for the automaker’s pickup trucks and SUVs.