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During the very cold weather (here in Ohio) recently, I noticed the brakes on my 2000 Chevy Malibu were a little soft, and made a mental note to attend to them promptly.
Then, over the course of 24 hours or so, they went from "a little soft" to "I had to use my parking brake to stop at stop lights."
I added brake fluid tonight, and over a 20 minute drive with 1/2 dozen or so stops, I noticed they still felt uber-soft, but if I pumped my brake pedal multiple times, they'd gain power.
Any ideas?
If you lost all (or almost all) of your brake fluid, you have a leak. Check all of your calipers (assuming disk brakes all around) to see if there is a leak at the wheels. If none there, check the soft lines (rubber lines at the wheel) for leaks. If no leaks there, check around the master cylinder and anti-lock brake unit for leaks from the lines. If you do not see any leaks here or puddles on the ground, your master cylinder may be leaking into the power booster. The only way I could tell you to check this is to disconnect the master cylinder from the brake booster and see if it is wet on the back side where it connects at the booster. This would be a long shot, but is possible.
If your reservoir is low, the fluid has to go somewhere. As @R.. stated, there is air in the lines after you added fluid to your reservoir, which would cause your brakes to be really spongy. I'm surprised they are working at all, really. You should not drive your vehicle until you get this figured out, not only for your safety, but for the safety of your passengers and other vehicles/drivers around you.
As R.. says, the remaining softness will be down to air in the lines - this can be fixed by properly bleeding the system.
Before you do that, however, you need to establish the cause of the loss - until you do so, the car should be regarded as dangerous and must not be used. If you're in any doubt, take it to a professional.
The most likely cause of a fluid leak is a failing seal in one (or more) of the cylinders. This can be obvious in some cases (fluid spurting out when you press the pedal), and not in others - the master cylinder can fail internally and leak into the servo... Failing flexi hoses can also lead to leaks, although this is less common, they normally cause other symptoms first.
I agree with the other posts.
First: Do not drive the car until this is fixed. You will NOT save money by wrecking your car and maybe putting yourself in the hospital.
Second: if you're going to do the work yourself, get a how-to manual. Brakes (and steering) are safety-critical systems; if they fail they put both you and those around you in danger. Don't pull an "I didn't know it was loaded!"
Your vehicle is 14 years old. During braking, some components get hot enough to smoke. This is plenty long enough for brake cylinders to corrode, seals to fail, and calipers to seize. Have you ever changed the fluid, replaced brake discs and pads, turned the rotors, etc.?
Components likely requiring replacement due to age (to save $$ you can go for rebuilt components):
