Your Guide To Vehicle's Brake Master Cylinder

When you're driving down the lane, and step on the brake pedal, you'll expect your vehicle to slow down before coming to a complete stop. This happens when all the brake-related components are functioning correctly. But this might not be the case if certain parts, like the Brake Master Cylinder, aren’t functioning correctly. Find out everything about Master Cylinder here.

What Is Master Cylinder?

The master cylinder is a hydraulic device in an automobile braking system in which the cylinder and one or two pistons are arranged in such a way that the mechanical force applied by the driver through the brake pedal, is converted into hydraulic pressure. This hydraulic pressure creates the necessary braking force to stop the vehicle. Without a master cylinder, there would be no hydraulic pressure and hence the brake force would also not transmit. Master cylinder consists of an arrangement of one or more pistons and is the first hydraulic component in any braking system.

What Are The Types Of Master Cylinder?

The various types of master cylinder are as follows:

  1. Single Circuit Master Cylinder - This type of master cylinder is just like a medical syringe. In this type of master cylinder single-piston inside a cylinder is used so that the braking can happen.
  2. Tandem Master Cylinder or Dual Circuit Master Cylinder - This is a modified type of master cylinder. This dual cylinder-dual piston or single cylinder dual-piston along with a dual circuit would be used for independent braking between the front and rear wheels. It is more efficient than a single circuit master cylinder. Hence, it is used in almost all cars.

What Are The Functions Of A Master Cylinder?

  • Applies Pressure To The Brakes: A brake-master cylinder transforms the brake pedal pressure into hydraulic power, resulting in brakes being operated on the automobile. The master cylinder operates similarly to a syringe; the brake fluid is pushed out of the cylinder toward the brakes when pressure is applied.
  • Brakes Safety: Most master brake cylinders feature 2 chambers with a pair of wheels each. In the event of a failure in the braking system by a damaged brake line or other problem, master cylinders are designed this way. If one set of brakes fails, the other set will still function. 
  • Stores Excess Fluid: To hold the excess brake fluid, a reservoir is built inside master cylinders. The fluid is forced into the brake line when the brakes are engaged, allowing brakes to function. The fluid can flow back into the reservoir if the brake pedal is released thereby releasing the brake syste
  • How Does The Master Cylinder Work?

    The working of the Master Cylinder is explained below:

    A. Single Circuit Master Cylinder

    • When the brake pedal is not pressed in the single circuit master cylinder - i.e. not actuating position - the piston stays in the original position, which then seals the input valve of the reservoir. As a result, no brake fluid enters from the reservoir to the compression chamber.
    • The piston connected to the brake pedal moves as the brake pedal is pushed, i.e. the actuated position. This opens the inlet valve, and the brake fluid enters from the reservoir into the compression chamber. 
    • The brake fluid inside the compression chamber is compressed because of the movement of the piston that is found inside the cylinder.
    • Following compression, the outlet valve is opened and the highly compressed brake fluid is sent to the brake lines for further brake actuation.

    B. Tandem Master Cylinder

    Its working is 70% similar to the single circuit master cylinder but in this type, two independent circuits of braking are utilized.

    • The tandem master cylinders function 70% the same as the single circuit master cylinder, but the 2 independent circuits of braking are used.
    • The piston stays in its original place when the brake pedal is not actuated. It closes the intake valve of both the compression chambers, which reduces the brake fluid input between the reservoir or both the reservoir chambers.
    • The primary piston moves first when the brake pedal is actuated and this opens the primary inlet valve. The brake fluid is initially compressed into the primary chamber because of the movements of the primary piston.
    • Once the compression is over, the primary outlet valve is opened and this compressed brake fluid is transferred via brake lines, and the primary circuit brakes are actuated.
    • When the primary piston movement has been completed, i.e. at its extreme end, the secondary piston starts to move because of the force produced by the primary piston, opening the second valve and the brake fluid is transferred from the secondary reservoir to the second compression chamber.
    • This brake fluid is then compressed and the secondary outlet is opened after complete compression. This highly compressed fluid is transferred via the brake lines to the brake calipers and secondary circuit brakes are actuated.

    What Are The Frequent Problems Faced By The Brake Master Cylinder?

    Have a look at some of the methods with which you can diagnose the most common problems associated with the master cylinder:

    1. Check the Brake Pressure - If there is a lack of brake pressure when you depress the brake pedal, then it is an indication that there may be some fault in the master cylinder.
    2. Check Brake Fluid Levels - Braking problems mostly arise in the master cylinder when the brake fluid level is low.
    3. Assess the Metal Brake Lines - The metal brake lines which connect the brake master cylinder can rot and then leakages can be developed. There can be leakage of the fluid through the O-rings inside the cylinder as well.
    4. Evaluate the Master Cylinder Grommets - A master cylinder has a plastic reservoir attached to it that holds the brake fluid. This reservoir is mounted on the metal part of the master cylinder by rubber grommets. Check these grommets if they are damaged.

    What Are The Symptoms Of Bad Brake Master Cylinder?

    Usually, a defective brake master cylinder might start showing the following symptoms:

    1. Abnormal brake pedal behavior - The first symptom which is generally related to a faulty brake master cylinder is the weird behavior of the brake pedal. It is the master cylinder that generates all of the pressure for the car braking system parts. If it develops any sort of problems then you may feel it in the pedal. Over time due to constant usage, the seals inside the cylinder can wear out and give rise to leaks. A defective brake master cylinder might result in a pedal that feels mushy, spongy, or it will slowly sink to the floor when it has been depressed.
    2. Contaminated brake fluid - One other symptom of a faulty master cylinder is that the brake fluid might be contaminated. Rubber seals are used by the brake master cylinders which can break down and then wear out over time. When this is done, it might contaminate the brake fluid, and then it would be turned into dark brown or black color. A worn-out seal in the brake master cylinder can cause leaks which reduces brake pressure giving rise to a sloppy brake pedal feel. 
    3. Check Engine Light comes on - You may see the check engine or brake warning light. There are brake fluid level and pressure sensors installed in the many modern master cylinders. The main purpose of these sensors is to find any issue with the automobile’s brake fluid pressure, which is produced by the master cylinder. If it is detected that there is a drop in the pressure, then it can due to some issues in the master cylinder. The brake master cylinder is the heart of the braking system and at the same time plays an important role in the handling and safety characteristics of the vehicle. If the brake master cylinder in an automobile does not operate in perfect condition, then the vehicle could be dangerous to drive. That is the reason if you find out that there are some defects in your brake master cylinder, then you must get your car brake system parts checked by an experienced technician.

    What Are The Tool Needed to Repair The Master Cylinder?

    If you want to repair your Master Cylinder all by yourself, then you will need some auto body tools. You can always start by building your own tool chest. Searching for some tools to repair your Master Cylinder? Don’t Worry! We are here to help you out. Here are some common tools that you will probably end up needing while repairing your Master Cylinder.

    Which Top Brand Brake Master Cylinder Should I Choose For My Vehicle?

    There are a number of car lovers who are emotionally attached to a specific brand for their car parts. So, if you are searching for a particular brand for your Master Cylinder, then you have arrived at the right place. Have a look below:

    1. Raybestos Master Cylinder & Power Booster
    2. Mr. Gasket Master Cylinder & Power Booster
    3. Dorman/Help Master Cylinder & Power Booster
    4. Cardone Industries Master Cylinder & Power Booster
    5. Blue Streak Master Cylinder & Power Booster
    6. Dorman Master Cylinder & Power Booster
    7. Dorman/First Stop Master Cylinder & Power Booster

    Which Parts Are Related To My Car's Brake Master Cylinder?

    Do you want to know the related parts of your vehicle's Brake Master Cylinder? Don’t worry! PartsAvatar Canada is here at your service.

    What Is The Total System Costs, Repair Times & Efforts Needed To Repair Brake Master Cylinder?

    There can be a number of factors due to which the failure in the master cylinder might be caused like poor car maintenance, some accident due to which the master cylinder might get damaged or there might be some flaws during the quality control check at the factory where the car was manufactured or sometimes it might happen because of not changing the master cylinder on time. Whatever the cause might be, the replacement of the master cylinder is not at all an easy process and if you want to achieve success, then it’s essential to have the correct tools. This is the reason why you should leave the replacement/repair procedure to skilled mechanics who have the tools and expertise to successfully complete the task. The replacement cost for the brake master cylinder can lie between $251 and $587.

    What Are The Steps To Change The Brake Master Cylinder?

    Here are some steps to change the master cylinder:

    Step 1

    Raise the hood and locate the brake master cylinder.

    Step 2

    Now remove the master cylinder. To avoid spillage, make sure to remove the old brake fluid as much as possible.

    Step 3

    Remove the fluid reservoir cap. Insert a turkey baster to get rid of the fluid and fix the cap again.

    Step 4

    Release the safety clip of the electrical connector. Now gently pull it from the fluid level sensor in the reservoir. 

    Step 5

    Use a line wrench and firmly secure it on the brake fluid lines to remove them. Repeat this process until the fluid lines are fully removed.

    Step 6

    As you loosen the lines, the brake fluid may leak. Use a shop towel below the master cylinder to catch the fluid. Discard the shop towel, once the task is complete. 

    Step 7

    Remove the mounting bolts of the master cylinder and push it forwards. Now lift the master cylinder off the mounting studs and then out of the engine compartment.

    Step 8

    Reinstall the new master cylinder.

    Step 9

    Once the job is complete, it is essential to bleed the entire braking system so that air from the system can be removed.

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    Replacing a master cylinder is not that difficult. But you'll need to be prepared. At times you will have to remove some of the components such as hoses or wires out of the way. But keep track of where they go along with fasteners, so as not to lose them.

    The brake master cylinder will need replacement at least once or twice in the vehicle’s lifetime. In fact, most master cylinders last over 160,000 km, before they need to be replaced.

    If you are driving with a bad master cylinder, then the brake fluid will start leaking due to internal damage. You may not be able to apply brakes, as the brake pedal could sink to the floor.

    The cost of the master cylinder can be between $260 to $360. Labor costs are estimated to be between $130 to $160 on average.

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    John Framigllia
    Technical Writer
    Our technical writer is known for simplifying automotive parts and services. Intuitive with various vehicles and manufacturers, he knows how to simplify complicated problems.