Dear Tom and Ray:

I have a four-wheel-drive 2005 Dodge Dakota with 32,000 miles on it. Since I had the front brake pads replaced four months ago, I have noticed a faint burning smell coming from the wheels after I drive to work. I took it back to the repair shop, and they could not find anything wrong. This weekend, I took it down a winding canyon road, and when I got to the bottom, there was smoke coming from the wheels, along with a strong burning smell. I took it to the Dodge dealer, and they can’t find anything wrong with the brakes –– nothing charred, no pulsation and plenty of pad left. Do you have any idea why my brakes are smoking?

TOM: Well, usually brakes smoke for one of two reasons, Sean. Either they’re being applied continually, or someone has offered them a good Cuban stogie.

RAY: Let’s assume that you’re not resting your foot on the brake pedal while you drive. We have to look at the parts of the brake system that can lead to the brakes staying on when your foot isn’t on the pedal.

TOM: One possibility is that your mechanic used some real cheap brake pads, and they’re too big for the caliper brackets. That can cause the pads to stay too close to the disc rotors and rub against them. But I’m guessing that when you took the truck to the Dodge dealer, they would have noticed that –– and taken the opportunity to sell you a new set of factory pads.

RAY: The second possibility is that you have a sticking caliper. The caliper is the device that squeezes the brake pads together around the disc rotor. If the caliper doesn’t release properly, it’ll keep the brakes applied while you drive.

TOM: And calipers can misbehave intermittently, and be hard to “catch in the act.” So, if you can narrow the smoking to one particular wheel, it might be worth trying a rebuilt caliper on that wheel to see if that solves the problem.

RAY: On the other hand, you do say in your letter that your brakes –– plural –– were smoking. And it’s unlikely that more than one caliper would get sticky at the same time. So if it really is all of the wheels, or at least both front wheels, then I’d go farther up the line, to something that could keep all the brakes applied.

TOM: That would be the power-brake booster. The booster uses vacuum to multiply the force that your foot applies to the brake pedal. When it’s failing, it can essentially “stick” in the boost, or “on,” position. That means it’s applying the brakes when you’re not.

RAY: And while that’s a nice display of initiative on the part of the brakes, it’s not an acceptable state of affairs. So ask your original mechanic to drive the truck for a day or two. If he can make it smoke, he can jump out and test the booster on the spot. Or at the very least, he can narrow it down to a specific wheel or wheels. Good luck, Sean.

Don’t top off

Dear Tom and Ray:

I got into an argument recently concerning whether I should top off when I fuel up. You know what I mean –– the pump shuts off, and I can either stop or put another half a gallon more in. Is that OK, or not? I notice some pumps say not to top off, and I was wondering why. Most reasons I have found online discuss fuel expansion, which, it seems to me, would be rather minimal. So now I am asking the experts . . . can you point me in the right direction?

RAY: Was the “argument” with a spouse, by any chance, Kurt? Who else would you ever get into an argument with at a gas station? Anyway, you owe her an apology, Kurt.

TOM: Vaporization is the problem. In the old days, gas caps used to have holes in them so gasoline vapors could escape. The vapors went right into the atmosphere, creating smog and preventing Sarah Palin from seeing Russia from her home in Alaska. Oh, and the other problem with smog: lung disease.

RAY: To solve the problem, the Environmental Protection Agency required that all cars come with a vapor recovery system. A key piece of that system is something called a charcoal canister, which is attached to the gas tank.

TOM: When the gasoline in the tank expands and creates vapors, those vapors are absorbed by the charcoal. They’re held there in the charcoal until the next time the car starts, and then the vapors are sucked back into the intake air, and burned by the engine during the combustion process.

RAY: When you top off your tank, you take the chance that you’ll force liquid gasoline into the charcoal canister, ruining it. And what does that mean? At least 300 bucks, Kurt.

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