Hydraulic System: Testing and Inspection

If signs of leakage are not present but the brake master cylinder is definitely low, it is possible that evidence of fluid leakage may have been washed off by rain or snow because brake fluid is water soluble. To determine if a leak exists, proceed as follows:
a. Refill the system
b. Bleed the system
c. Apply the brakes several times
d. Examine the system to verify that the brake master cylinder reservoir level is actually dropping
e. Locate and correct the external leak

Internal and external leaks are two problems that can affect a brake hydraulic system. The hydraulic brake system will not cause the vehicle to do any of the following:
^ Vibrate
^ Grab
^ Squeal
^ Allow the brake pedal to pulse

In most cases the hydraulic system will not even cause the brakes to drag. The sources of these problems are found elsewhere in the brake system, but it is always a good policy to first check the entire hydraulic system for leaks before continuing to diagnose any other brake problems.