When brakes go to the floor, run, don’t walk, to a mechanic

Dear Car Talk:

I have a 2001 Monte Carlo SS, and when I step on the brakes, the pedal goes all the way to the floor, but the car doesn’t stop at all. Pads and fluid are good. Is it the master brake cylinder?

— Kasey

Well, that sounds exciting, Kasey. If you lived long enough to read this, you’ll be heartened to know that your guess probably is correct.

If you don’t have a massive leak, it probably is the brake master cylinder. The master cylinder is basically a hydraulic pump filled with brake fluid. There’s a piston inside it — like in a bicycle pump. And when you step on the brake pedal — you push that piston, which forces the hydraulic fluid, under pressure, out to the brakes.

And typically, the way master cylinders fail is that the seals around the piston fail. So when you push the piston, the fluid just sneaks around it, rather than getting pushed out to the brakes. That leads to exclamations that contain two words, the first of which is “Oh.”

And master cylinders often fail intermittently. While they’re in the process of dying, they can work poorly in cold weather, and then, when the seals around the piston heat up and expand, they can work better.

But you don’t want to mess around with a car that doesn’t stop, do you, Kasey?

I guess we should compliment you on being a very calm individual. You must have very low blood pressure. Normally, when someone’s brakes go to the floor, he or she doesn’t go home, calmly write a letter to some automotive columnist and hope they publish an answer in the next few weeks.

So I hope you didn’t wait for our reply before taking action, but if you did, don’t wait any longer. Go get it fixed now.

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