Brake Hydraulic System Inspection
It is important to repair worn brake hydraulics because neglected hydraulic systems can cause expensive repairs or serious accidents. The condition of the brake hydraulics can be evaluated without taking the wheels off. The fluid of a rarely driven vehicle will likely be contaminated with atmospheric moisture and pollution, and will deteriorate rubber components beyond safety standards.
High humidity climates damage brake fluid faster because DOT 3 and DOT 4 brake fluids attract atmospheric moisture. DOT 5 brake fluids don’t attract the moisture but foams up when ABS activates. Mileage is another factor in brake hydraulic system health. The master and wheel seals wear with use, and will eventually fail usually around the 100,000-mile mark.
Brake System Configuration
Always determine the hardware configuration before recommending an inspection, diagnosis, or service. In modern vehicles, an ABS light will light up as a warning. In pre-1990s vehicles, if there is no ABS light, then the car doesn’t have ABS, and a red warning light will illuminate as a warning. The proportioning valve keeps the rear brakes from locking up during panic stops. Some trucks incorporate a rear brake-metering valve that gives more pressure when the truck is fully loaded. ABS has functionally replaced most of the combination/metering valve hardware configurations.
Master Cylinder Inspection
The first step in a brake inspection is to investigate the illuminated ABS or Brake light using a scanning tool. The ABS or Brake light can mean numerous things depending on the make or model of the vehicle. Physical inspections should begin with the fluid level. Low fluid usually indicates worn pads. Check for external leakage and if there is none, then loosen the master cylinder and check the rear master cylinder seal. Fluid condition is a good indicator of the condition of the hydraulic system condition. Heavy residue can indicate fluid contamination. Moisture contamination can be fixed by repeatedly flushing the system. Oil contamination can only be fixed by replacing all of the rubber seals and fluid.
Start the car and turn the wheel to full lock to check the brake hose for problems. Next inspect brake lines for rust or other damage and while inspecting the brake hose and lines, check for fluid leakage. Oil or fluid that leaks onto the brake friction can cause locking and the friction will need to be replaced.
When road testing a brake performance complaint remember the vehicle is potentially unsafe. Always check the master cylinder fluid level, and the holding power of the parking brake. Movement or sinking of the parking brake/pedal could need replacement or adjustment. To complete the inspection take a short test-drive around the parking lot to find the worst of the problems. During any service, always perform a complete inspection of the brake hydraulic and friction systems.