Sales of medium- and heavy-duty trucks fell 22.6 percent in August from a year earlier to 24,569 units.
Sales of Class 4-8 trucks haven't increased since January 2007. The pace of the decline had eased in July, when sales fell just 7.8 percent. That was the first single-digit drop this year.
But the collapse resumed in August.
Sales of large trucks were mixed. Class 7 trucks took the biggest hit in sales last month, dropping 45.2 percent to 3,370 units. In contrast, sales of Class 8 vehicles climbed 9.2 percent to 10,722 units.
Sales of Class 5 trucks tumbled 26.4 percent to 2,815 units. Class 6 sales plummeted 44.7 percent to 2,750 units.
Sales of Class 4 trucks followed the overall trend in August, dropping 29.6 percent to 4,912 units.
International led the pack in August truck sales with 5,317 units, up 3.9 percent. Freightliner finished second with sales of 5,012 large trucks, up 5.8 percent. Only three brands posted higher sales in August: International, Freightliner and Mack. Mack's Class 8 truck sales edged up 0.4 percent to 827.
Year-to-date sales for Class 4-8 fell 21.0 percent from the year-earlier period to 222,133 trucks.