Billionaire investor Carl Icahn has taken a 9.8 percent stake in truck maker Navistar International, according to a filing yesterday with the Securities and Exchange Commission.

Icahn is known for targeting companies he views as undervalued and pushing for changes, such as new management, to boost shareholder value.

Navistar has seen its profit improve as demand rebounded from a severe slump that started in 2007. The manufacturer last month forecast a continued surge in orders for large trucks next year, though it cut its 2011 profit guidance as parts shortages crimped margins.

The company’s shares jumped 8.6 percent to $42 in after-hours trading on the news. The stock had been off 33 percent this year.

Icahn believes the shares are undervalued at current levels and has had conversations with Navistar’s management about the business, the filing said. He has also discussed placing his candidates on the company’s board but has not reached any agreement to do so, according to the filing.

A company spokeswoman declined to discuss Icahn’s stake, citing a policy of not commenting on individual investors, but said that “Navistar is always open to dialogue with its investors that can enhance shareholder value.”