The brake master cylinder on a Jeep (as well as other vehicles) contains most of the brake fluid and sends it to the brakes when the brake pedal is applied. It is mounted to the Jeep's brake booster within the engine and includes a large plastic reservoir that holds the majority of fluid. If you need to remove the master cylinder from the Jeep, use caution in dealing with the fluid inside. Brake fluid is a very corrosive liquid that will damage car paint, among other things, so protect all surfaces on the Jeep and do your best to avoid spilling the brake fluid as you remove the master cylinder.
Siphon out as much brake fluid as you can from the master cylinder reservoir. You can use any of several tools, including a siphon, poultry baster, large syringe or suction gun. Never use any of these for any other task, however, once you have used it to remove the fluid.
Disconnect the negative cable from the Jeep's battery. Place rags on the floor underneath the brake line fittings and cover any painted surfaces near the area.
Loosen the nuts connecting the brake lines to the master cylinder using a flare-nut wrench. Pull away the lines and plug them with rubber plugs to keep the system from getting contaminated.
Unplug the electrical connector to the fluid level switch, which is the connector with the wires located to the side near the reservoir. Remove the nuts mounting the master cylinder to the brake booster and remove the cylinder, making sure you don't kink the hydraulic lines as you remove it.
Unscrew the cap to the master cylinder reservoir and properly dispose of all remaining brake fluid in the reservoir.
