Volkswagen, Ford and PSA/Peugeot-Citroen were the hardest hit as French auto registrations dropped 11 percent last month, challenging hopes for a swift stabilization of the market for new cars.

Car registrations fell to 85,565 in August, a slow holiday month from which it is harder to extrapolate trends, France’s CCFA industry group said today.

Sales for the first eight months of the year were down 10 percent, but the CCFA maintained its full-year forecast of an 8 percent decline.

“September and October will be critical,” CCFA spokesman Francois Roudier said. “August is always a thin month, but this year it’s particularly low.”

Volkswagen Group had the biggest monthly sales decline in France with a 24 percent drop, mainly attributable to weaker sales at its core brand.

Ford Motor and PSA were among mass automakers that fared poorly, with respective declines of 19 percent and 17 percent.

General Motors’ 16 percent sales gain defied the slump thanks to the Chevrolet brand, which recorded 2,429 car sales, up 64 percent. Fiat deliveries also gained 10 percent, and Renault achieved a 2 percent rise.

Daimler’s Mercedes-Benz brand recorded just 1,927 French August car registrations, down 37 percent year-on-year. The plunge reflects a French sales ban imposed on several Mercedes models in a dispute over air-conditioning refrigerants, lifted by a court injunction last week.