Replacing a Faulty Brake Master Cylinder

November 6, 2013

A brake master cylinder is a difficult item to replace without proper knowledge, but after reading this article you will have the knowledge needed.

Removing Old Fluid

Before you can remove the master cylinder, you must remove all of the fluid from the old master cylinder. The tool needed is known as a "vacula." It is a vacuum machine with a small tube and a plastic container. After removing all of the fluid from the old master cylinder, it is recommended to bleed all of the fluid from the brake lines to prevent contamination of the new brake fluid.

Everything You Need to Know about Brake Fluid >>

Master Cylinder Removal

Begin the process by loosening the brake lines that run to the master cylinder. There should be approximately 4 brake lines connected to the master cylinder. Once the lines are securely out of the way, you can remove the two to four bolts that hold the master cylinder to the brake booster. Once the bolts are removed the master cylinder should pull out of the engine compartment.

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Cleaning and Transferring Parts

Your new master cylinder will probably not come with the reservoir so you will need to remove the one form the old master cylinder. Different vehicles are removed in different ways, but the majority of them simply pull off. Once you have the reservoir removed, thoroughly clean the inside of it to make certain there is no debris left inside. Now you can simply press it on the new part and you are ready to install.

Installation of New Master Cylinder

This is done by simply lining up the new master cylinder on the brake booster, making certain a new gasket is in place. Next tighten the bolts to manufacturer specification. Now it is time to reinstall the brake lines. Make certain certain not to cross thread the fittings, and then you can simply tighten them onto the new part.

Filling and Bleeding the Master Cylinder

Now you want to add DOT 3 brake fluid to the new master. Initially, you can fill the master all the way to the top. Now, you will want to press the brakes until you feel the brake pedal stiffen. At this point, you want to gravity bleed the brakes by leaving the bleeder screw on each caliper loose for about 15 minutes. Now you want to do a complete bleed. For this process you will need a friend to help you. Start by having your friend pump the brakes until stiff and hold them. While you friend holds the brakes, you loosen the bleeder screw. Do this process until nothing but brake fluid flows from the bleeder screw on each caliper.

Final Check and Test Drive

Now that the installation is complete, you need to check the fluid level. This step is usually performed incorrectly; you only want to add as much fluid as you have brake pad remaining. If you only have about 50% brake pad remaining then only fill up to the middle between the “full” and “low” line this lets you know when the pads are low.

Now you can test drive the vehicle and you are completed.

Learn more about Brake Repairs >>

Related Questions and Answers

Do You Need a Brake Bleeder Tool to Bleed Brakes?

A brake bleeder tool is not a necessary piece of equipment required to bleed brakes. The bare minimum requirement is a wrench or socket to loosen the bleeder nozzle. Of course, if you want to be neat, you should also use a small diameter hose, like a vacuum line; and a container to catch the used brake fluid. Additionally, you will need the assistance of a second person to pump the brake pedal while you loosen the bleeder nozzle. The bleeding process is complete when the new, clean brake fluid finally flows from the bleeder nozzle.

For more info, see Replacing a Faulty Brake Master Cylinder

Does a Pressure Brake Bleeder Work Better than other Types?

A pressure brake bleeder is usually used by repair shops because it allows the job to be performed by one worker. This system works by applying pressure at the master cylinder, which causes brake fluid to be pushed to each of the wheels and out of the loosened bleeder nozzles. However, by attaching the device to the master cylinder, and applying pressure, the piston seals within the master cylinder may be damaged. The master cylinder was designed to work by allowing brake fluid to flow into the piston using gravity. The better way to bleed brakes is pumping the brake pedal, and bleeding the fluid one wheel at a time.

For more info, see Replacing a Faulty Brake Master Cylinder

What are the Most Common Master Cylinder Problems?

There aren't very many master cylinder problems. in fact, the majority of the time, the problem is due to leaking and/or worn piston seals. Worn seals are something to be expected because they are being used each time you apply the brakes. However, leaking seals are typically caused by dirty or contaminated brake fluid. Bake fluid is subjected to extreme heat and pressure, and over time, degrades. If it is not changed, and brakes are not bled on a regular basis, contaminants in the fluid will tear at the seals and cause them to leak.

For more info, see Replacing a Faulty Brake Master Cylinder

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