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When to Replace a Brake Master Cylinder
Whether you know how to replace a master cylinder or not, the first step is to identify when it needs to be changed. You’ll need to diagnose it completely since many of the symptoms are the same as when other brake components are bad. Symptoms can include:
- Visible leaks at the master cylinder. Often, it’s an integrated fluid reservoir, a seam, or the plunger inside that leak.
- Brake pedal fade. A soft, spongy, or inconsistent pedal can signify that the master cylinder is allowing air into the hydraulic system.
- Pulling when you brake. If the hydraulic output is uneven, the brakes can cause a pull to one side.
Tools and Equipment Required
Replacing a brake master cylinder requires several pieces of equipment and tools such as:
- Floor jack and jack stands
- Flat screwdriver or pry bar
- Wrench set
- Ratchet and socket set
- New brake master cylinder
- Appropriate brake fluid
- Brake cleaner
- Brake bleeder kit
- Drain pan
Steps to Replace a Brake Master Cylinder
Set aside at least a few hours to replace your brake master cylinder. Even if you’re an experienced tech of backyard mechanic, there’s always the potential for a stage of the process to go sideways.
1. Prepare the Vehicle
Before you can replace a brake master cylinder, get your vehicle ready, and use safety equipment such as eyewear and protective gloves before starting any type of automotive repair or maintenance. You will also need to elevate the vehicle in order to properly access the brake calipers or wheel cylinders after the repair, so use jacks and stands for this task. Also be sure to set the parking brake and loosen the wheels’ lug nuts while your vehicle is still on the ground – this way they’re easier to remove when you lift up your car or truck.
2. Remove the Old Master Cylinder
Before installing a new brake master cylinder, the old one needs to be removed. First, locate the brake lines connected to the master cylinder. Once you’ve identified these, use an appropriate wrench or socket along with some penetrating oil and carefully loosen each line until they can be removed without any debris getting inside of them. Finally, unscrew the mounting bolts that attach the master cylinder itself and then pull it away from its position. Put the old master cylinder in a drain pan to prevent brake fluid from dripping. It can damage any painted surfaces in seconds.
3. Install the New Master Cylinder
Before installing the new master cylinder, make sure you’ve thoroughly cleaned the area inside the engine compartment. Then, bench bleed the new master cylinder by pressing the plunger for 10 to 15 seconds at a time until it no longer can be pressed in more than 1/8-inch. Transfer hydraulic lines from the old master cylinder if necessary, then install it onto the brake booster, making sure that it’s evenly tightened on both sides. Once secure, tighten the brake lines in place. Test for any leaks before bleeding your brakes. Finally, don’t forget to top up your brake fluid reservoir afterward.
4. Bleed the Brakes
After the brake master cylinder has been successfully installed, it is essential to bleed the brakes to ensure you have a consistent brake feel and the right performance. It’s a good practice to start bleeding the brakes at the wheel farthest from the master cylinder and then move around to each wheel in the next closest proximity until all of them have had their brakes bled. During this process, either a second person or a brake bleeder kit should be used. And you’re finished when there are no air bubbles left coming out of the lines. If this procedure is followed correctly, you can rest assured that your vehicle will have effective brakes.
Tips and Precautions
Replacing a brake master cylinder should be completed with caution.
- Make sure to safely lift the vehicle before attempting this repair, and ensure that all necessary tools are on hand.
- Pay special attention to the brake lines and clamps, as it is important not to crack a line and lose brake fluid.
- Finally, make sure to check for leaks after the job is complete and tighten all fittings before returning the vehicle back to the ground.
Replacing a brake master cylinder is a job that must be done correctly for the brakes to be effective and safe. If done properly, your vehicle’s braking system will remain reliable and, with the right tools and techniques, anyone with enough knowledge should feel comfortable delving into this repair job. If you decide that it’s too big a job to tackle on your own, let your local AutoZone help you find qualified professional mechanics through our Shop Referral Program.
FAQ/People Also Ask
Can I drive with a bad brake master cylinder?
It’s ill advised to drive with a bad brake master cylinder since you can’t be confident the brakes will work as designed.
How long does it take to replace a brake master cylinder?
It can take between one and four hours to replace a brake master cylinder depending on your skill level and the type of vehicle you’re working on.
Can I replace a brake master cylinder myself?
If you have the tools, it’s possible to change it on your own. Follow the service manual precisely to ensure the job is done properly.
How much does it cost to replace a brake master cylinder?
It depends. Parts range from around $30 to more than $200, and you’ll also need fluid. If you have a mechanic perform the job for you, it’s likely you’ll need to pay a couple hundred dollars more.
How often should a brake master cylinder be replaced?
There’s no reason to replace a brake master cylinder unless it has failed, so there’s no mileage or time specified to do the job.
