The big manufacturing news on Tuesday was that American auto sales were up 13% in September, to nearly 1.2 million vehicles. Small vehicles led the month's good performance, now making up 23% of new vehicle sales. Consumer expectations of prolonged high gas prices or increasing interest in being environmentally friendly may have contributed to the strong sales of small, fuel-efficient, and hybrid vehicles. Despite the industry's big improvement, the major automakers saw drastically different results, leading to divergence in share prices.

By percentage, the biggest winners were Japanese importers Toyota Motors (NYSE: TM) and Honda Motors (NYSE: HMC), which increased their American year-on-year sales by 42% and 31%, respectively. However, in 2011 both companies were recovering from the devastating earthquake and tsunami that hit Japan in March of that year, causing major supply and inventory problems. Since the market expected these drastic sales increases, both companies were essentially flat: Toyota was down 0.3% and Honda lost 0.03%.

More surprising was the performance of boutique all-electric luxury-car maker Tesla Motors (Nasdaq: TSLA). The company's sales are too small to make any difference in the national figures, but its announcement that it planned to deliver more than 200 of its Model S sports sedans was enough to send shares up 2.2%. Investors may also be cheered that electric vehicles generally are gaining acceptance, as the Chevrolet Volt reached its highest monthly sales figure in its history, delivering 2,851 vehicles in September. Tesla investors will need to see that trend accelerate, as the company is valued quite highly for a business that has yet to turn a profit.

Chrysler, majority-owned by Italian carmaker Fiat, turned in the strongest sales of the Detroit Three: 12% sales growth, driven by the mid-size Dodge Avenger and compact Dodge Dart. General Motors (NYSE: GM) came in second, with total auto sales up 1.5%. This figure disguised some big discrepancies in product mix as the company transitions away from its former bread-and-butter truck sales and toward smaller cars. Sales of its Chevy Cruze were up 29% in September, while sales of its top-selling vehicle, the Chevy Silverado pickup truck, declined 17%. For a company that used to be addicted to truck and SUV sales, I'm pleased to see GM focused on selling smaller vehicles and growing sales while doing it.

Ford (NYSE: F) came out on bottom in September, losing a bit of ground as sales fell 0.1%. The company is seeing a similar trend as General Motors -- car sales rising 1.6% and truck sales falling 7.6%. Ford blamed that poor performance on the discontinuation of its popular Ranger pickup truck, and U.S. sales analyst Erich Merkle warned that only about half of Ranger customers are staying with Ford vehicles for their next purchase.

Ford is already undergoing prolonged trouble in Europe and is behind rival GM in breaking into the Chinese market. Does weakness in North American sales mean investors should slam on the brakes? Not necessarily: September may have simply been a fluke, since Ford is currently in between models of its popular Fusion sedan, which typically makes up 12% of sales. In fact, the company's "One Ford" plan to integrate vehicle platforms, trim development costs, and break new sales territory may only just be starting to bear fruit.

One Motley Fool analyst thinks Ford's best years are still ahead. Our premium report on Ford breaks down the opportunities and risks the company faces, and it comes with a full year of analyst updates. This report is available for only a limited time, so get your copy now.