My car's gear shifted while driving yesterday afternoon. The gear has lost its function. It didn't transmit the changes I made to the transmission. I pulled to the right and stopped immediately. I looked under the car, opened the hood and looked at the bottom of the engine. I couldn't see anything. I called my motor master friend in the industry. He came, looked at the gear. Then he got angry at me and opened the hood. "Don't call me again for such simple things," he said as he stretched towards the bottom of the engine. He rechecked the gear and said, "He will handle it for a few days, let's change the piece on a worn Saturday." It had never happened to me before. Does anyone know what this fault might have been caused by?