U.S. auto sales in September for GM, Ford and Chrysler beat estimates, showing some gains in the still sluggish auto market.

Sales for the biggest U.S. automaker fell about 6 percent from August but were up 10.5 percent over September of last year.

GM sold some 172,969 vehicles in September of 2010. Of the core brands, Buick sales were up 36 percent, Cadillac was up 11 percent, while Chevrolet was up 19 percent. GMC sales were up 46 percent.

There were no adjustments for sales days, as this September had the same number as September 2009. CNBC reports auto sales figures based on the same number of sales days from year to year.

Ford [F  12.25  0.01  (+0.08%) ] says it's sale were up 46 percent in September, beating the estimate of 37.9 percent, seeing strong sales of redesigned cars and trucks.

Ford had expected sales to rise significantly from September of 2009, when sales dropped as last summer's Cash for Clunkers program came to an end.

The automaker says sales also rose 2 percent from August of this year. Ford says sales of its redesigned Ford Edge and Lincoln MKX set monthly records. The new subcompact Fiesta also drew buyers into showrooms.

Chrysler also reported sales, with a 61 percent increase in September, beating the 43 percent estimate by analysts .Chrysler has struggled with sales much of the year because of an aging model lineup. But the Grand Cherokee is the first of a string of new or updated models due out this year.

Chrysler says the new Jeep Grand Cherokee helped. The redesigned sport utility vehicle saw sales nearly double over September of last year.

As for GM, it spent about $3,300 in incentives per vehicle on average to close sales in September. That represented a discount of about 10.7 percent of the average cost—in line with the industry's average.

"Consumers are sending a very clear message that they will be cautious with their spending," GM sales chief Don Johnson told reporters and analysts.

Johnson said GM would remain disciplined in pricing and avoid the temptation to rely on more aggressive discounts to drive sales volumes.

"It's the economic recovery that has to drive our sales," he said. "Is it slower than everyone would like? Potentially," Johnson said.

GM was restructured in a bankruptcy funded by the Obama administration and the government is counting on an IPO to reduce its nearly 61 percent stake in the automaker.

Automakers will be reporting sales figures all day. They were expected to post solid gains in September, relative to last year's cash-for-clunkers hangover, with strong retail numbers boosting hopes for an upbeat finish to the year.

Industry analysts say this September started strong. Labor Day promotions spurred buying, but customers backed off toward the end of the month.

Auto analyst firm J.D. Power expected the retail annual selling rate to be about 9.4 million units for September, below its earlier 9.7 million estimate. The researcher said retail transactions are a more accurate measurement of true underlying consumer demand for new vehicles.

Industry-wide sales for September face an unusually easy comparison to 2009 when the auto sales rate was an anemic 9.2 million vehicles.

That exceptionally weak sales rate represented what analysts called a "hangover" from the expiration of the U.S. government's popular cash-for-clunkers sales incentives a month earlier.

For that reason, many analysts will look at the comparison between September and August sales rates for a better sense of the trend.