D.C.-based Carlyle Group and Toronto’s Onex Corp. have purchased a General Motors-owned transmission operation for $5.6 billion.

The companies bought GM’s Allison Transmission, a Speedway, Ind.-based firm. Under the agreement, the investment firms would take control of the company’s seven manufacturing facilities in Indiana and other assets. Allison employs 3,400 people and generates annual revenue of more than $2 billion. It produces transmissions for trucks, buses and military vehicles. GM will maintain control of Allison’s manufacturing plant in Baltimore.