Mack Trucks Inc. and its parent, AB Volvo, will pay $525 million to settle a class-action lawsuit filed by more than 9,300 retirees of the North Carolina truck maker after they challenged potential reductions to their lifetime health benefits.

The Legal Intelligencer reported Tuesday that Senior U.S. District Judge R. Barclay Surrick gave preliminary approval of the settlement. A hearing is Sept. 7 to decide if the settlement is fair and reasonable.

The suit was filed in Michigan after Mack sought a ruling that lifetime benefits of its retirees were not vested and could be modified or eliminated. Both cases were consolidated in the Eastern District of Pennsylvania.

Mack reached an agreement with the UAW in May of 2009 on a voluntary employees beneficiary association, or VEBA, that would have the union oversee retirees' health benefits. Mack and Volvo agreed to fund it with $525 million, paid in five annual installments.

Mack said it expects the final approval of the VEBA in September.

The company also reported that deliveries nearly doubled in April from a year earlier with 1,608 trucks delivered from the 810 it recorded in April 2010, an increase of 99 percent.