The National Highway Traffic Safety Administration (NHTSA) has opened an investigation into reported transmission problems in 2011 and 2012 Ford Mustangs.

The preliminary evaluation stems from 32 complaints filed with the agency regarding an occasional problem shifting into gear in six and eight-cylinder cars equipped with a 6-speed manual transmission that is manufactured in China. Approximately 26,000 of the cars have been sold.

Many of the reports focus on a difficulty engaging 1st, 2nd and 3rd gears during both up- and downshifts, especially when the transmission is cold. Others mention a persistent grinding sound and issues with other gears. In addition to the official complaints filed with NHTSA, the topic has appeared on a number of independent websites that cater to Mustang owners. No accidents or injuries have been reported, but several of the complaints mention close calls that were caused as a result of the problem.

Ford has previously addressed an operating issue with the transmissions, which are produced at a facility run as a joint venture between Ford and German transmission specialist Getrag. In March, the automaker issued a technical service bulletin (TSB) instructing service technicians to replace the type of transmission fluid installed at the factory with a different specification that is less susceptible to increased viscosity, the resistance of a fluid to flow, at low temperatures.

Nevertheless, at least one owner alleges that he or she has continued to experience the problem even after the change has been made. The complaint from July 27th, 2011 reads, in part:

"FLUID SWAP DONE, GRINDING WORSE IN 2ND-4TH GEARS. 2ND GEAR LOCKOUT IN LEFT TURN AT 45 DEGREES. 4TH GEAR RATTLE UPON WOT [wide open throttle.] VEHICLE NO LONGER FUN TO DRIVE, WAITING TO GET RID OF IT AS LEMON."

A separate TSB issued by Ford in November, 2010 cautioned that loose clutch bolts could cause difficulty shifting into first gear or reverse.

A FoxNews.com analysis of the recent NHTSA complaints indicates that a number of the owners may not be aware of a special feature found on V8-powered Mustangs that forces the transmission to shift directly from 1st to 4th gear under light throttle application. This is intended to increase fuel efficiency during the EPA fuel economy testing procedure and cannot be turned off, but is overridden during hard acceleration. The manual transmissions in the Chevrolet Corvette and Camaro SS, both built by a different supplier, function in a similar way.

A Ford spokesman tells FoxNews.com the company is "working with the government as they review the matter, and will fully cooperate."

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