Freezing temperatures affect power-brake booster

February 24, 2012

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 F 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


— 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


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 poke around and figure

out exactly 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


* * *

Get more Click and Clack in their new

book, “Ask Click and Clack: Answers

from Car Talk.” Got a question about

cars? Write to Click and Clack in care of

this newspaper, or e-mail them by visiting

the Car Talk Web site at


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