See Figures 1, 2 and 3
On models through 1971, the master cylinder is located under the floor. To check the level of the brake fluid remove the floor plate. Clean the area of all dirt so that, when you remove the cover, no dirt will fall in and contaminate the brake fluid. Dirt in the hydraulic system could score the inside of the master cylinder or wheel cylinders and cause leakage or brake failure. Unscrew the lid of the master cylinder with a wrench. The fluid level should be within 1 / 2 inches from the top of the reservoir chamber. Use only heavy duty brake fluid and keep it away from any other fluids or vapors that could contaminate it.
On 1972 and later Jeep vehicles, the master cylinder is located under the hood, on the left side of the firewall. To check the fluid, use a screwdriver to pry off the retaining clip from the lid of the reservoir. The fluid level should be within 1 / 4 in. (6mm) of the top of the reservoir.
If the master cylinder is less than half full, there is probably a leak somewhere in the hydraulic system. Investigate the problem before driving the vehicle.