Check out this great article I found on doityourself.com, about diagnosing brake problems:
As any thinking adult knows, automobile brake problems are among the
most important of factors to be considered when you are driving a car. Once an
accident has occurred because of faulty brakes it is too late to begin looking
for brake defects that might have caused the accident. The best time to look for
potential brake problems is when you first detect signs of a possible problem,
such as those described below. But to do this you will need to know what
telltale signs to look for. Use the steps below to identify brake problems
before they can create safety hazards.
Step 1 - Brake Noises
When you hear a noise from your car as you apply your brakes, such as
scraping, grinding, or any other noise that is abnormal, you should immediately
check your brakes for worn shoes or pads. Linings contaminated with break fluid
can also make a noise that can be identified as a potential problem, as well
as loose brake components or lack of proper lubrication. You should immediately
investigate any of these noises.
Step 2 - Investigate a Need for Using Excessive Brake Pressure
Recognize immediately any need for excessive brake pressure. This could be
caused by a defective brake booster, brake fluid, water on your car's brake
linings or a possible defect in one of your brake system parts. At times, such
as with water on your brake linings, this problem may be temporary. But if the
problem persists, be sure to have your brakes checked and have all defects
Step 3 - Identify and Check Out Brake Drag
If, after stopping, then starting forward again in your car you notice that
the brakes are not releasing the instant you release your brake pedal, this
could be an indication of a brake Problem. A cylinder piston may be stuck, a
defective master cylinder, brake pad, or even a parking break may have failed to
release. This is a serious cause for you to check your brake system.
Step 4 - Excessive Brake Pedal Movement
Check your brake shoes or failing pressure check valve if, when you step on
your brake pedal, it depresses more than 3 or 4 inches toward the floor before
the brakes begin to activate and your car begins slowing. It is also possible
that your brake shoes are not properly adjusted.
Step 5 - Check Vibration in your Steering Wheel or Brake Pedal
Vibration from your brake pedal or steering wheel when you depress your brake
pedal may be an indication of a brake disc or drum that is warped. When you
feel this vibration you should immediately examine your brake system or take
your car to an auto service shop where they can check and repair any defect in
your braking system.
Step 6 - Absence of Brake Pedal Pressure
Investigate possible defects in your brake's caliper piston, wheel cylinder,
a break or clog in your brake fluid hose, a defect in the brake booster, or
contaminated pads or shoes when your pedal sinks almost to the floorboards when
applied. These are all symptoms of possible brake defects or failure and should
be checked right away.
Read more: http://www.doityourself.com/stry/how-to-properly-diagnose-a-brake-problem/#ixzz23A5AorVV