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Master Cylinder Replacement – When Should A Master Cylinder Be Replaced?

Master Cylinder Replacement

The master cylinder is the device that has the job of converting force or pressure – from a driver’s foot- into hydraulic pressure. The master cylinder also powers slave cylinders which can be found at the other end of the hydraulic system.

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So, when this component becomes faulty, you are at risk of accident and other issues. 

When Should A Master Cylinder Be Replaced? 

The fluid that travels throughout the braking system in your vehicle, is there to offer the needed pressure that brings your vehicle to a complete stop. If you don’t have the proper amount of brake fluid in your vehicle, then it is virtually impossible to bring your car to a complete stop. Your vehicle’s master cylinder has the brake fluid in it and it disperses that fluid to various parts of your vehicle’s brake system as needed. Typically, the master cylinder will have a reservoir that houses the fluid. Additionally, your vehicle’s master cylinder is deployed only when the driver of the vehicle depresses on the brake pedal Insufficient brake fluid in the master cylinder can damage the entire braking system of a vehicle. 

The master cylinder is a component that is built to last as long as a vehicle does. But sometimes, it may not make it that long or far. As the master cylinder has seals that can become dry, cracked, brittle and fragile, those seals are vital to operation. Without great working master cylinder seals, the master cylinder may begin to leak as well as break down with constant usage. We as drivers use our braking system- more than we perhaps realize. In fact, the braking system in our vehicle is a system that we constantly use without full awreness. From stop and go driving, to slowing down for animals and more- you simply cannot drive a car without a braking system. So, with fractured seals on a master cylinder, the component will then need to be replaced. 


 When your master cylinder begins to break down and go out, there will be various issues that you will begin to notice. So, what are those warning signs you should be looking for? Check out some of the most common issues that indicate it’s time to replace your master cylinder: 

  • You’ll have brake fluid levels that are lower than normal. 
  • You will exert more effort to bring your car to a complete stop. 
  • Your braking will feel “soft” or “spongy”. 
  • You will notice brake fluid leaks. 
  • Your brake light will illuminate on your dash. 

Once you have low brake fluid due to a master cylinder that is leaking, you are looking at a multitude of issues. So, if this is the case for you, then you are looking at a master cylinder that needs to be replaced immediately.  The warning signs that your car gives you regarding your damaged master cylinder should not be ignored under any circumstance. 


How Do You Test A Brake Master Cylinder?

When you choose to examine the master cylinder, you want to ensure that you have adequate brake fluid. This is fluid that is stored in your vehicle’s master cylinder. As we mentioned earlier in our article, once you step on the brake pedal, the fluid then flows from the master cylinder to the vehicle’s brake lines. As you release the brake pedal, the fluid will then go back to the master cylinder. Check out the following steps for checking your brake fluid in your vehicle’s master cylinder: 

Open the brake fluid reservoir that you will see on the top of your master cylinder

Do you have a reservoir that looks like a plastic bottle located on top? Then all you have to do is just take the cap and jut unscrew the cap that is on the little plastic bottle, which sits on top of the master cylinder. Is your vehicle outfitted with a metal reservoir? Then you can take a screwdriver and pry the retaining clamp from its position.  Try not to let any debris or dirt fall into the chambers as you open the lid. Do you have a hood that has lots of dirt and grime? Then take some time to wipe the lid before removal. 


Look at your lid and evaluate it 

When the brake fluid retreats or goes back in your master cylinder- or when it is forced into the brake lines- the master cylinder’s diaphragm cups are going to be forced in a downward position by air that is traveling through vents that are in the lid. The cups will then descend. Eventually, they will then touch the surface of the brake fluid that remains- to keep evaporation at bay, as well as keep debris, dirt and dust out.  Once the fluid flows back in, the cups will then to into an upward position. You may see that your brake fluid is low. If this is the case, of if you see that your cups are in a descended position after you take off the lid, then take the cups and push them back up with a dry finger before you replace your lid. 


Check out the inside of your master cylinder 

The brake fluid in your vehicle should be at the “fill” or the “full” line. If it’s not, then you need to purchase the proper brake fluid for your car and carefully fill it up. After you fill it up, you want to ensure that you close it rather quickly. You don’t want water vapor or oxygen to contaminate the fluid. Another tip that we want to mention is this: please do not allow any fluid to drip anywhere as the fluid can eat away at your car paint!


Check the chambers of your master cylinder 

Are both chambers of your master cylinder filled with brake fluid? Is that fluid at the proper levels? Then you can now close the master cylinder while making sure that no dirt or debris fall into it. Lots of master cylinders are quite airtight. Therefore, you should not lose any brake fluid unless you have a leak. 


Check for marks or streaks

Look closely for any leaks or issues as you finish checking the master cylinder. You may want to get a flashlight and check for any wetness, gunk, debris or stain marks that may be under the master cylinder.


How Hard Is It To Replace A Master Cylinder?

Replacing a brake master cylinder is not a hard task for many vehicle models. But you do need to have patience, experience and preparation. To replace your master cylinder, you will may have to take off various hoses, wires and other components to gain access to it. So, as you remove items, don’t forget where they go, after you replace it.  Be sure to keep track of where each component goes, as well as their clips and fasteners. You certainly don’t want to lose anything during a master cylinder replacement job. 


You’ll have to bleed the system 

The master cylinder has the task of transforming the brake pedal pressure into hydraulic pressure. This is done to stop or bring the vehicle to a halt. Once you bleed the system, you will allow the brand-new master cylinder- as well as your brakes- to have proper function and operation. 

In order to successfully bleed your system, you’ll need help or a hand-held vacuum pump if you’re replacing the master cylinder by yourself. Check out your local auto parts store and find out if they will allow you to borrow the vacuum as well as other tools, for your master cylinder replacement job.

Before you begin replacing your master cylinder… 

  • Become familiar with the entire process and ensure that you are able to perform the job on your particular vehicle. 
  • Make sure that you have ALL of the tools you need for the master cylinder replacement job.  Do a check and if you don’t, please do not begin the job and stop to obtain or get a tool. 
  • Choose how you’re going to bleed your vehicle’s brake system after you install the new master cylinder.


Steps Required To Replacing Master Cylinder 

Check out these steps to replacing your master cylinder. 

Removal of the old fluid 

The first step in replacing your master cylinder is to remove the existing brake master cylinder using a vacula. A vacula is a machine that has a plastic container alongside a vacuum machine outfitted with a small tube. Take your time in flushing out the old fluid, ensuring that your brake lines are also clean. This helps to prevent new fluid from being contaminated during the replacement process.  


Removal of the old master cylinder 

For this, carefully loosen the brake lines that run throughout to the master cylinder. After such, you can then unscrew the bolts that are attached to the master cylinder, on the brake booster. After you loosen the screws, you can now pull the master cylinder out of the engine housing. 


Clean the parts and transfer them 

Your new master cylinder may not be outfitted with a reservoir. No need to worry. Just detach the reservoir from the previous or the old master cylinder. For most, you can just pull on the reservoir to remove it.  After the reservoir is out, make sure that you clean it completely, ensuring that you remove all debris, gunk and dirt.  After you finished cleaning the reservoir simply push it on the new part and begin installing the new master cylinder.


Master Cylinder Alignment 

As you begin to place the new master cylinder into the vehicle, you want to make sure that you take the time to align the new master cylinder with the brake booster. Don’t forget to place a new gasket there too. Then continue on with tightening the bolts. Next,  move towards replacing your vehicle’s brake lines. 

Make sure that you’re careful during the entire process. You don’t want to cross the thread. Afterward, make sure that all is tightened properly. 


Fill as well as bleed your master cylinder 

You’ve now successfully installed the new reservoir as well as the brakes lines. Now the time has come for you to fill your newly installed master cylinder. For this first time, you can top off your master cylinder to the optimum level. Begin my depressing the brakes, till you feel that your brake pedal has stiffened.  Then, loosen your calipers and give them a chance to stay loose for about 15 minutes so that gravity can secure successful bleeding. 


Do you want to perform a total bleed? Then ask someone to help you with the process. Get a friend to push the brake pedal till it stiffens and then old them afterward. As your friend is pushing on the brake pedal, you can then slowly loosen the bleeder screws. Continue with this process till you see the brake fluid flow from that bleeder screw. After all is done, you want to ensure that your fluid level is in accordance with your vehicle’s brake pads. Are your brake pads standing at 50%? Then keep the fluid level in between the “full” and the “low” line. Now is the time you can test drive your vehicle to see if all is well. 


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