The master cylinder reservoir is located on the left side of the firewall. Several different types are used. Older styles have a metal cap secured by a wire bale. Other versions use screw-on caps or a one-piece snap-on plastic cap.
If an inspection window is provided, check fluid level relative to the mark(s). Add fluid if level is at or near the "MIN" mark.
On master cylinders with screw-on caps, the level should reach the bottom of the filler hole ring.
On older style master cylinders (one-piece metal caps), the level should be about 1 / 4 in. below the reservoir lip.
Before removing a reservoir cap, clean all dirt away from the top of the master cylinder
There is a rubber diaphragm in the top of the master cylinder cap. As the fluid level falls in the reservoir due to normal brake wear, the diaphragm takes up the space. This is to keep air out of the system due to sloshing as well as to prevent leaks. Make sure to inspect this cap for any tears or cracks, it will require replacement if any damage has occurred.
After refilling the master cylinder to the proper level (using the proper brake fluid), but before installing the cap, be sure to fold the rubber diaphragm up into the cap. Then install the cap in the reservoir and tighten the retaining bolt or snap the retaining clip into place.
If the level of the brake fluid is less than half the volume of the reservoir, it is advised that you check the brake system for leaks. Leaks in the hydraulic brake system most commonly occur at the wheel.