Installing a master cylinder is normally a two-person job. Once the part has been installed on the car, it will be necessary to bleed the brakes of air pockets that develop when the system has been opened. This requires specialized equipment or an assistant. Individual steel brake lines are routed from the master cylinder to the front and rear brakes. Some systems use four separate lines, while others use two lines that split to serve the left and right front and the left and right rear. Regardless of the system, these lines are opened and removed in order to replace the defective part. Air will enter the lines and it must be removed.
Remove the brake fluid lines from the master cylinder. The lines are held in place by specialty nuts that allow the fluid tubes to pass through their center and have threads on their outer surface. These nuts have far less structural integrity than a nut with inner threads that tighten against a solid bolt. The force a standard, open-end wrench applies to these unsupported nuts is in two places---not enough to successfully grip the nut and loosen it. A line wrench, designed for this purpose, slips over the line then onto the nut, gripping it in six places instead of two. Unless a line wrench is used, the nut will round over and be difficult to loosen.
Remove the two mounting bolts holding the master cylinder in place against the firewall. Wrap the master cylinder in old rags to absorb any brake fluid that will leak out. Brake fluid is very damaging to paint and leaves a stain that cannot be buffed out.
Bench bleed the master cylinder. Mount the new master cylinder in a shop vise, remove the filler cap and add new brake fluid. Mount the body of the master cylinder as level as possible to prevent air pockets developing when new fluid is added. Wrap the tip of a large Phillips screwdriver with a shop rag and press it against the valve end of the master cylinder. Lean against the screwdriver, using body weight to push the valve in and out several times. Fluid will spray out of the line ports. Use a shop rag to contain the spray.
Install the new master cylinder. Fasten the two mounting bolts and install the brake lines. Use caution and do no cross-thread the line nuts. Start each one by hand and make sure they are perfectly aligned as they are tightened.
Bleed the brakes. Have an assistant lightly pump the brake pedal, then hold steady pressure against it. Open a bleeder valve at the right-rear wheel. Close the valve after the assistant states the break pedal is completely depressed to the floor. Tighten the valve and repeat the process of lightly pumping the brake pedal and holding pressure, opening the valve to remove the air while the brake pedal goes to the floor and closing the valve. Do this at each wheel in the order of distance from the master cylinder, the right-rear being the most distant, followed by the left-rear, the right-front and finally the closest, the left-front. This method is used to minimize the risk of any air remaining in the brake lines.
