Diagnose the problem with a high-speed shake test.

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Dear Car Talk: I have a 2004 Saturn Vue. Recently I took it in for new tires. While my car was on the lift, it was discovered to have a totally worn-out mid-driveshaft bearing. There was a half-inch gap of play around it. I wondered how it could be so worn out and not be creating side effects, like noise. When I asked the service manager if the shaft turns all the time, he replied, “Yes.” But now I have had time to analyze it a bit myself, and I think since it is an all-wheel-drive car, the shaft turns only when it goes into all-wheel-drive mode. For me, that is almost never. Can you tell me the true story on this? — Douglas

A: I believe your Vue’s driveshaft turns all the time, Douglas. All-wheel-drive vehicles work in different ways, but I believe the Vue sends power to all of the wheels all of the time.

The bearing for that driveshaft lives inside a rubber housing. So it’s designed to be able to flex a little bit. But if it’s truly worn out, as the mechanic says, you’d feel a wicked vibration at high speeds.

Do you ever drive at high speeds, Douglas? I wouldn’t blame you if you refused to in this car. But next time you do, see if you lose any fillings. Because a worn-out driveshaft bearing would rattle the car very noticeably at highway speeds.

If you don’t notice a vibration at high speeds, then you probably don’t need to do anything. Maybe the mechanic mistook the built-in flex for a worn-out bearing — a half-inch is probably about right. Or maybe it really is wearing out but isn’t bad enough to replace yet. Or perhaps the guy just had a boat payment due that week.

But if it makes you feel better, get a second opinion. Hopefully it’ll be something besides ” … and your car is ugly, too.” Good luck, Douglas.

Got a question about cars?
Contact Ray through the website cartalk.com.