Ford will notify about 740,000 owners of 2004 Explorers and Mercury Mountaineers of a potential transmission problem in the popular sport-utility vehicles.

Ford spokeswoman Kristen Kinley told Reuters the automaker will be sending out letters asking customers to take their SUVs to a dealership for free repairs.

Ford decided to send out the notification following complaints that the SUVs' transmissions fail to engage smoothly, or make a noise when shifting from park to reverse, Kinley reportedly said.

Reuters said the National Highway Traffic Safety Administration has received a number of complaints from Ford customers about the problem. No recall notice has been issued, but the problem with the Explorer, which is America's best-selling SUV, could put a dent in recent claims of improved quality at the second-largest US automaker, the news agency noted.

"We are in the process of a service repair procedure," Kinley told Reuters, adding that Ford dealers were already repairing some vehicles that have the problem.

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