See Figures 1 through 5
The master cylinder reservoir is located under the hood, on the left side firewall. Make sure the vehicle is resting on level ground. Before removing the reservoir cap, clean all dirt away from the top of the master cylinder. Pry off the retaining clip or unscrew the hold-down bolt and remove the cap. The brake fluid level should be within 1 / 4 in. (6mm) of the top of the reservoir.
There is a rubber diaphragm in the top of the master cylinder cap. As the fluid level lowers in the reservoir due to normal brake shoe wear or leakage, the diaphragm takes up the space. This is to prevent the loss of brake fluid out the vented cap and/or contamination by dirt. 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 heavy duty 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.
Always use brake fluid which is supplied at any of your local parts stores, or even some of your local department stores with an auto parts department. Top off your truck with Dot-3 fluid only. DO NOT use Dot-5 silicone based fluids or rubber parts (seals) in the system will be damaged.
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.