How to Check the Brake System of my vehicle?

The brake system is often checked by the mechanic during routine oil changes and maintenance. However, it can also be checked at home. Consult the service manual of the specific make and model about checking the brakes and finding the locations of each part of the brake system. Follow these steps to check the brake system:

If there is any variation in the brake pad (or shoe) thickness between the driver side and passenger side, then there may be an adjustment problem, a defective caliper or other defective hardware. Usually the front brakes wear faster since the front brakes are responsible for about 80% of the stopping. There is no blanket measurement for brake pad thickness since the thickness of new pads can vary by make and model of the vehicle. A few millimeters could appear brand new in one car but be an indication for pad replacement in another. If the thickness of the pad is 20% of the original thickness or less, then the pads should be replaced. The original thickness can be found in the service manual for the vehicle.

Open the brake fluid reservoir on top of your master cylinder.
If you have the kind with a little plastic bottle on top, just unscrew the cap on the little plastic bottle that sits on top of the master cylinder. If you have a metal reservoir, use a screwdriver to pry the retaining clamp off the top.
Take a look at the lid.
As the brake fluid in your master cylinder recedes (when it’s forced into the brake lines), the diaphragm cups are pushed down by air that comes in through vents in the lid. The cups descend and touch the surface of the remaining brake fluid to prevent evaporation and to keep the dust and dirt out. When the fluid flows back in, the cups are pushed back up.
Look inside the master cylinder
The brake fluid should be up to the “Full” line on the side of the cylinder or within 1⁄2 inch of the top of each chamber. If it isn’t, buy the proper brake fluid for your vehicle and add it until the level meets the line.
If both chambers of your master cylinder are filled with brake fluid to the proper level, close the master cylinder carefully, without letting any dirt fall into it. Because most master cylinders are pretty airtight, you shouldn’t lose brake fluid in any quantity unless it’s leaking out somewhere else.
Use a flashlight to look for stain marks, wetness, or gunk under the master cylinder.
If your master cylinder is — or has been — leaking, you’ll see evidence of it when you look closely.

Typical full-lock operating pressures on conventional OEM-style automotive hydraulic-brake systems are 900–1,000 psi with manual brakes and 1,400-plus psi with power-assisted brakes. To check the pressure, you’ll need a simple brake-pressure gauge. They’re sold by several sources, including Lamb (PN 882) and Wilwood (PN 260-0966). Use the gauge to check pressure at each caliper or drum and at each master-cylinder outlet port. (Deactivate or bypass any proportioning valve or ABS computer.) If the pressure is much lower at one or more wheels than it is up at the master cylinder, the problem is in the lines or at the calipers and drums. If there’s high pressure everywhere but the brakes don’t lock up, the master cylinder and calipers or drums are mismatched or incompatible. If pressure is low everywhere, look at the master cylinder, the power-assist unit (if applicable), or brake pedal.