RAY: Hi! We're back. You're listening to Car Talk with us, Click and Clack, the Tappett Brothers, and we're here to talk about cars, car repair, and, duh, the answer to last week's Puzzler.

TOM: Another great answer to another great Puzzler.

RAY: Indeed.

TOM: Yeah.

RAY: This was sent in by Bob Gossam, and he says, some time ago, I married a woman with a Datsun B210, the famous Honey Bee. Small, noisy, reliable, and fun, both the car and the wife, he says. One day, I pushed on the brake pedal and it went almost to the floor. I had owned a VW where this happened all the time, so I didn't panic. I just pumped it a little and it came back. Anyway, I had the brakes checked out from stem to stern, but there were no leaks, no problems with the master cylinder. The calipers in the front were fine. The wheel cylinders in the rear were OK. But still the problem persisted, but only occasionally. It sounds so good, doesn't it? After much observation, I determined it only happened with the car had been driven above 40 miles per hour for 10 minutes or more. Around town, no problem. Quick trip on the freeway, no problem. 10 minutes on the freeway, and the first time you touched the brake pedal, rrrrp! Right to the floor.

TOM: Man!

RAY: After that, if I hit it again, the pedal would be OK, unless I continued to drive on the freeway, in which case it would happen again at 10-minute intervals, or roughly some such thing. You got it?

TOM: Yeah.

RAY: Of course, he must have gotten gun shy of stepping on the brake.

TOM: Yeah.

RAY: Keep looking at your watch, and while you do that, you crash the car.

TOM: Can't stop right now!

RAY: Anyway, he says, I took it to garage after garage, and they'd never find any problem with the brakes. One day, I'm having a beer with an engineer friend of mine, and I tell him about the problem in all the gory details. And just before he nodded off, he asks me one question, and then told me what was wrong. And the question was, did you buy something recently for this car? And of course, I told him, yes I did. The question was, what did he buy? And what was wrong?

TOM: What did he buy? Wow.

RAY: And it was not a pine tree air freshener.

TOM: I have no idea.

RAY: I was going to give an additional hint. I should have, perhaps. That he could have said, yes, I bought two of them.

TOM: Oh! I got it. Floor mats.

RAY: I can always count on my brother for thinking outside the box. What he bought was a new tire, and when they installed the tire on the car, they didn't balance it correctly, or didn't balance it, perhaps, at all. And as the car is going down the road and the thing is shaking, it is setting up a sympathetic vibration in the disc rotor, which is moving the caliper piston away from the disc, so that when you step on the brake that first time, the pedal will travel almost to the floor. We've seen this happen with cars whose wheel bearings are loose.

TOM: I actually like this answer.

RAY: And when you step on it that first time, that caliper has to move.

TOM: Has to move much further away.

RAY: Because that caliper piston is now not touching the brake pad. And then finally, when it does make contact, the second pump --

TOM: Bingo!!

RAY: -- is OK. And of course, you drive along for 10 more minutes, the vibration occurs. And he said it was undetectable, virtually, because the car had so many other vibrations and moans and groans or whatever, he never noticed it. And the hint was that it was a Datsun B210.

TOM: No, I like that answer!

RAY: Well, I'm glad!

TOM: That's great!

RAY: Anyway, who's our winner, Tommy?

[ Car Talk Puzzler ]