Click & Clack: Power-brake booster may need replacing

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Dear Tom and Ray:

I love your show, and I desperately need your help. I am presently the “keeper” of my 25-year-old daughter’s 2004 Nissan Maxima. It has a serious problem, which she also has mentioned. On any cold (34 degrees or below) winter morning, the power brakes are nonexistent. Like, gone for the first five to seven minutes after starting the car.

If you let the car warm up for 10 minutes, they’ll kick in. But if you try to head right out onto the road (which I have been crazy enough to try), you have virtually no brakes. I can pump the brakes really hard and ease to a stop if going less than 1 mph — seriously.

Mechanics have suggested everything from the transmission to the master cylinder to a brake line to a vacuum problem. Please help! I don’t want to be a kamikaze driver anymore! — Sharon

RAY: We don’t want you to be one either, Sharon. After all, we could be in the car in front of you.

TOM: The first thing I’d suspect would be the power-brake booster.

RAY: The power-brake booster is a device that uses a vacuum-operated diaphragm to multiply the pressure your foot applies to the brake pedal. It’s the “power” in power brakes.

TOM: If water has gotten inside the diaphragm, or into the line that runs to it, it could be freezing overnight and preventing the booster from working because the ice is blocking the flow of air.

RAY: Then, once the engine compartment heats up, the ice melts and the booster works normally.

TOM: We’re so used to having power brakes these days that when the “power” part fails, it feels like we have no brakes at all. And today’s heavier cars are much harder to stop without power brakes.

RAY: This should be pretty easy to diagnose, Sharon. One option is to simply put a booster in it. I think there’s at least an 86.75 percent chance that that will solve your problem.

TOM: Otherwise, you’ll have to leave the car overnight with your mechanic.

RAY: First thing in the morning, while the brakes are actually misbehaving, your mechanic can figure out what’s going on.

TOM: In the meantime, stay off the road until your brakes are fully functioning. Remember, body work generally is a lot more expensive than power-brake boosters.

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