This week on Car Talk, Carolyn needs an intervention. Her safety-minded husband has her wearing a bike helmet behind the wheel. Need we say nerd alert! Then it's off to MD with Stephanie, whose clutch is going on her Mazda. Can her hubby fix it himself, or will she be doomed to the bus for the next six months? All that, plus a new puzzler from Ray's Jalopy series, on this week's geek-filled hour of Car Talk.