The auto industry's move away from rental fleet sales weighed heavily on overall July results.

Three of the biggest names in the auto industry reported weaker-than-expected July sales numbers Tuesday morning, sending Ford Motor Co (F - Get Report) and General Motors Co (GM - Get Report) stock down, while Fiat Chrysler Automobiles (FCAU - Get Report) shares were barely higher in mid-morning trading.

The auto industry's move away from rental fleet sales to companies such as Hertz Global Holdings (HTZ - Get Report) and Avis Budget Group (CAR - Get Report) weighed heavily on weaker July results. Barclays said in a Monday note that overall industry sales into rental fleets were down nearly 20% year-over-year in the second quarter, suggesting a trend that could continue into the third quarter.

But overall retail car sales took a big hit as well.

Ford's overall July sales slumped 7.5% compared to July of last year to 200,212 vehicles sold, a larger dip than Kelley Blue Book's 6.2% sales decline estimate.

The drop was driven largely by a 26.4% decline in fleet sales. Ford said half the decline in fleet sales comes from lower transit sales tied to recall delivery holds.

Ford retail sales were down 1%, truck sales were down 7.1% and car sales were down 19.4%. SUV sales ticked up 2.2% and hit a year-to-date record of 472,022. Ford said the SUV success positions the company well for the upcoming release of Expedition and EcoSport models.

Ford's days' supply inventory levels were flat compared to July 2016. The company's stock traded down nearly 3% mid-morning.

GM July U.S. sales tumbled 14% from last year to 202,220 vehicles sold, representing a weaker-than-expected performance compared to Kelley's 9.1% decline prediction.

The company reported its best monthly mix of sales ever, though, with 80% of sales coming from crossovers and trucks. The Chevy Equinox and Bolt, GMC Acadia, Buick Envision and Cadillac XT5 had their best July months ever.

GM's commercial sales are up 11% year-to-date and 40% from last July, led by strong sales in large vans, small utilities and large pickup models.

Daily rental sales accounted for only 1% of GM's sales in July, down 81% from last year. GM has the lowest U.S. rental mix in its industry at about 7% of sales so far this year.

The company predicted that they'll end 2017 at or below last year's vehicle inventory levels, with fewer cars and more trucks, crossovers and utilities in the mix. GM stock dipped about 3.5% mid-morning.

Fiat Chrysler reported a 10% decrease in total sales from July of 2016, down to 161,477 units and weaker than Kelley's 6.9% sales decrease estimate.

Retail sales dipped 6% and represented 90% of total sales at 145,391 vehicles. Sales to the daily rental segment shrank 35% year-over-year.

The company's Jeep Compass, Chrysler Pacifica and Ram ProMaster City had their best July sales months ever. Fiat Chrysler stock traded slightly up mid-morning.

More of What's Trending on TheStreet: