Dear Car Talk:

I'm 72, and I have a 2007 Ford Focus. At unpredictable intervals, my brake pedal goes all the way to the floor. This happens in wet weather every few months. It happened again last night. I had driven for about five or six minutes, and the pedal went all the way to the floor. My car just kept rolling right along. I have learned to pump the pedal, and it corrects itself and works fine after that ... until it happens again, a few months later. The dealer says it is not happening. But it IS happening, and I'm afraid it will cause my death eventually. Do you have any idea what could be done to prevent this?

-- Catherine

No, but you might want to tie a king-size air mattress to your front bumper until you figure it out, Catherine.

Actually, I think your dealer is acting unconscionably by telling you it's not happening -- and by sending you back on the roads without attempting to fix it. Send copies of those repair orders, where he wrote that, to the executor of your will, so at least your heirs can own the dealership if this does cause your death.

But we'd rather make sure it doesn't. So tell your dealer to start by replacing your brake master cylinder. Based on the symptoms, that's the most likely culprit. A bad master cylinder can fail intermittently, and then regain pressure.

A stuck brake or parking brake also can cause this condition by causing your brake fluid to boil and your brakes to fail. But that's unlikely to happen after only five or six minutes of driving, so I'd lean toward the master cylinder.

They have to try something. They can't just let you drive around with disappearing brakes. So have the dealer put in a master cylinder, and hope that solves the problem. And if not, have them make their next best guess, whatever it is, and try another brake system component. You have to get to the bottom of this, Catherine, before you end up in the package compartment of a stopped UPS truck. Good luck!