The truck unit of Volkswagen AG has offered to fully take over Navistar International Corp. in an all-cash transaction valued at roughly $2.9 billion. A deal would combine two of the world’s largest truck makers.

Traton SE, which was formed out of Volkswagen’s Truck and Bus Group, owns a 16.76% stake in Navistar.

Germany-based Traton has made an unsolicited bid to acquire the remaining Navistar stake for $35 a share, representing a 45% premium on the company’s closing price of $24.07 a share on Thursday. This would put Navistar’s total valuation at $3.5 billion. Shares in Navistar rose 51% in after-hours trading.

Navistar said Thursday that it would carefully review and evaluate the proposal.

Volkswagen offered as much as 11.5% of Traton last June in an initial public offering of stock.