General Motors Corp. on Thursday said it reached a deal to sell its Allison Transmission unit for $5.6 billion to private-equity firms Carlyle Group and Onex Corp.

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.

GM had said in January that it was looking to sell Allison, which makes transmissions for commercial trucks, buses and military vehicles.