Pete Cordaro was creeping down a dirt road in his 2013 Tesla Model S electric car, on a Sunday outing with his wife to hunt mushrooms in the Pennsylvania woods, when he encountered a pothole and then heard a loud crack.

“The front of the car just dropped,” he said. “The left front wheel just detached from the car.”

When Tesla picked up his car, Mr. Cordaro was at first told he would have to pay for the repairs because they were from normal wear. After pressing his case with a Tesla manager, he was told the company would pay part of the cost — as long as he signed a nondisclosure agreement.

Neither the equipment breakdown nor the confidentiality demand turned out to be an isolated case. And now they have Tesla Motors on the defensive.

After the nation’s top auto safety regulator raised questions about reports of suspension problems with the Model S, Tesla declared in a blog post on Friday that the suspension system had no safety defects. But what set the case apart from other auto safety episodes was the introduction of a nondisclosure agreement into the relationship between car owner and automaker — an unusual practice by an unconventional company whose founder, Elon Musk, has roots in Silicon Valley, not Detroit.