Never put off brake work. If you are experiencing any of these signs of brake issues, take care of the situation immediately.

If your brakes fail, you (and other people) may be in serious trouble.

Step on the pedal and press it down while paying attention to how the pedal feels under your foot and evaluating the sensation.

You need to get someone to look at them if:

• It feels spongy If so, you probably have air in your brake lines.
• The pedal seem to sink slowly to the floor rather than feeling firm If the pedal sinks, it's unsafe. With power brakes, the pedal should stop 1 to 1-1⁄2 inches from the floor. (If you don't have power brakes, the pedal should stop more than 3 inches from the floor.)
• If your vehicle has power brakes and stopping seems to take excessive effort
• Pumping the pedal makes the car stop when the pedal's higher up

Also get your brakes checked if:

• If the vehicle travels too far before coming to a stop in city traffic
• The vehicle pulls to one side when you brake
• The brake pedal pulsate up and down when you stop in a non-emergency situation
• The steering wheel shakes when you brake
• Your vehicle bounces up and down when you stop short -your shock absorbers may need to be replaced.
• The brakes squeal when you stop fairly short?
• The brakes make a grinding noise that you can feel in the pedal - If so, stop driving immediately and have your vehicle towed to a brake repair shop.

Source: Dummies.com