GM, Ford and Chrysler reported September sales declines on Thursday, revealing a tough hangover from this summer's Cash for Clunkers buying spree.

General Motors Co. reported the steepest drop, 45 percent, when compared with September of last year. Chrysler Group LLC was down 42 percent and Ford Motor Co. had a much smaller decline of 5.1 percent.

Automakers got a big lift in July and August from clunkers, which spurred sales of nearly 700,000 new cars and trucks. The government program's big discounts lured in many customers who otherwise would have waited until later in the year to walk into dealerships.

Now automakers are starting to feel the effect. GM said it sold 155,679 vehicles last month compared with 282,806 in September of last year. Ford reported sales of 114,241 in September, but the decline followed two straight months of rising sales. Chrysler sold only 62,197 vehicles last month.

GM blamed the decline on the clunkers program pulling buyers into July and August, weak consumer confidence and low inventory levels during September before production increases could replenish stocks.

"As expected, the market returned to pre-Cash for Clunkers levels in September," Mark LaNeve, GM's vice president of U.S. sales, said in a statement. "Fortunately the fourth quarter looks brighter."

Ford's top analyst told reporters on Thursday he does not think the Cash for Clunkers hangover will affect sales in October and beyond.

"I think most part the payback for the program will be minimal in the coming months," George Pipas said. "I don't think we should be using any excuses. I think from now on the economy stands on its own."

Cash for Clunkers and summertime production cuts kept inventories of popular models low during the month, but even so, Chrysler predicted its market share will rise 0.8 percentage points from August levels. The company increased factory output to replenish supplies.

"While we had some bright spots in September, it was still a challenging sales environment for the industry," Peter Fong, CEO of the Chrysler brand, said in a statement.

Sales of Ford's popular F-series trucks rose 3.5 percent, while sales of the new 2010 Taurus sedan increased more than 60 percent.

Ken Czubay, Ford's vice president of U.S. marketing and sales, said that could be a key indicator that pickup sales are starting to recover among core buyers who need them for work, and it may be an early indicator that small business owners are experiencing a turnaround.

"It's two months in a row of F-series sales increases for us," Czubay told reporters during a conference call. "It's not the large commercial purchases, it's more the individual."

The F-series trucks usually are the top-selling vehicle in the U.S.

The September results fell 37.2 percent from August totals, which were boosted by the government's Cash for Clunkers program. Two of Ford's vehicles — the Focus and Escape — were top sellers in the program that ran during July and August and offered big discounts to buyers.

Sales of the those vehicles posted steep declines from from August to September. Focus fell 64.1 percent from August, when Ford sold 25,547 of the small, fuel efficient cars. The company sold 9,182 in September.

The Escape crossover posted a month-over-month sales decline of 58.5 percent, with Ford selling 8,692 of the vehicles last month, compared to 20,933 August sales.

Chrysler also saw a slowdown between August and September. The company's sales fell by a third to 62,197 from 93,222 in August.

South Korean automaker Hyundai was an exception in September. Its sales jumped 27 percent year over year on easy comparisions to a weak year-ago period and strong demand for its Elantra and Santa Fe models.

Automakers sold a combined 1.3 million vehicles in August for a seasonally adjusted sales rate, or SAAR, of 14.1 million. Many analysts expect a SAAR of 9.3 million for September.

Shares of Ford fell 19 cents, or 2.6 percent, to $7.02 in afternoon trading.

Click here for more auto news and reviews from FOX Car Report