General Motors Co. posted strong August sales at three of its four remaining brands.

But Chevrolet, struggling with tough comparisons against last year's cash-for-clunkers bonanza, posted a 22 percent drop in sales, dragging overall demand for the automaker's core brands down 11 percent last month, Automotive News reported.

GM's sales -- including discontinued brands -- dropped 25 percent, while industry sales fell 21 percent.

GM's biggest division couldn't match August 2009 -- when Chevrolet recorded the bulk of its 86,000 sales under the clunkers program. The program provided incentives of up to $4,500 for shoppers who turned in older-model gas guzzlers for more fuel-efficient models.

Additionally, Chevrolet's 3,000 dealers have low stockpiles of the Cobalt compact as the division prepares to introduce a new compact -- the Cruze -- in late September.

Retail sales of Chevrolet's full-sized trucks and SUVs -- Silverado, Avalanche, Tahoe and Suburban -- rose 8 percent.

GM's other three brands -- Cadillac, Buick and GMC -- posted a combined monthly sales gain of 37 percent.

Cadillac's sales increased 83 percent for the month, and Buick saw a 66 percent gain. GMC was up 12 percent.

Cadillac sales received a shot in the arm from a 209 percent increase in August sales of the SRX crossover. CTS sedan sales were up about 61 percent.

Demand for the Buick Lucerne rose 62 percent, and the LaCrosse jumped 90 percent.

GM continued to reduce fleet sales in August. About 28 percent of the automaker's sales -- or 51,951 units among the four brands -- were to fleet customers. That's down slightly from a year-to-date fleet percentage of 31 percent.

Don Johnson, vice president for GM's U.S. sales operations, said he expects better performance by Chevrolet in the coming months.

In addition to the Cruze launch, GM plans to boost production of the Chevrolet Equinox and GMC Terrain to relieve shortages of the hot-selling crossovers in the coming weeks, Johnson said.