Brake Master Cylinder Replacement

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What is a Brake Master Cylinder?

A brake master cylinder is part of the braking system in your vehicle and is what helps your vehicle come to a stop when you apply the brakes. When you press the brake pedal, the cylinder converts the force into hydraulic pressure, and this pressure forces fluid through the brake lines ultimately stopping the vehicle.

The master cylinder contains brake fluid, a pushrod, two pistons, and springs behind the pistons.

How does a Brake Master Cylinder work?

When force is applied on the brake pedal, it pushes a rod aptly called the pushrod which pushes the pistons into the fluid and down the lines into the slave cylinders. The slave cylinders are located on the brake calipers and force the friction material (brake pads) onto the rotor.

When the brake pedal is released, the springs behind the pistons push back and pull the brake pad away from the disc brakes, disengaging the brakes.

Brake-Fluid reservoir

Located above the master cylinder is a reservoir filled with brake fluid. This reservoir should always be filled to avoid air from entering the system. Most master cylinders control two hydraulic circuits, each circuit controlling two wheels. This helps bring the car to a halt even if one of the circuits were to fail.

What is the life of a brake master cylinder?

A master cylinder is built to last for as long as the car does but can sometimes develop leaks or might fail and will need to be rebuilt or replaced.

It also helps the cylinder remain in good condition if the brake fluid is changed and flushed every 2 to 3 years rather than doing it only when something breaks.

When should a brake master cylinder be replaced?

The cylinder should be replaced if:

There are external leaks

Check for fluid on the external surfaces of the master cylinder or the reservoir. Check for fluid on the ground, beneath the brake pedal.

A spongy feel to the brakes

One reason for this could be because of air getting into the master cylinder.

Internal leaks because of faulty piston seals

This causes a “spongy” feeling or a pedal that sinks slowly as you maintain pressure.

Collapsing brakes

If the brakes collapse when you press the brake pedal it could be due to the plungers inside the master cylinder not being able to produce the required pressure.

Discolored brake fluid

Discoloration can occur because of moisture and contamination.

Warning lights on the dashboard

There could be several reasons for the warning lights, but the primary reason could be a faulty master cylinder.

Replacing the Brake Master Cylinder

Step 1: On vehicles with power brakes, the master cylinder is bolted to the metal housing of the power *brake booster. There is usually an electrical plug connecting to a brake fluid level sensor on the master cylinder reservoir and that plug must be disconnected.
Disconnect all steel brake lines from the master cylinder, unbolt the cylinder from the brake booster and remove it from the vehicle.

Step 2: Bench-bleed the new master cylinder to ensure that air is not trapped in passages containing the piston.

Step 3: Bolt the master cylinder back to the brake booster and reattach the brake lines. Reconnect the electrical plug for the fluid level sensor. Make sure to check all brake lines for leaks. Brake lines going to the wheels need to be bled to remove air, old fluid, and contaminants.

*(A Brake Booster is a device that increases the force applied from the brake pedal to the master cylinder. The booster is what separates a power-assisted braking system from a manual one).

Cost of replacement of Brake Master Cylinder

Depending on the model of the vehicle, it costs anywhere between $275 to $475 to replace a master cylinder.

Precautions to take if your master cylinder is defective

If you feel that your brakes aren’t working properly, do not ignore the problem. Get your vehicle inspected as soon as you can.

Even if the brakes don’t collapse but you feel that not enough pressure is being applied when you press the brake pedal, get your vehicle checked. Less pressure being applied will result in your car not being able to stop as expected and may lead to problems.

To avoid sudden failures, stick to a strict maintenance schedule as recommended by your vehicle manufacturer.

Can a Brake Master Cylinder be fixed or repaired?

The most common type of repair will be fixing a leak in the seals after they wear out every few years. It is not a difficult job but will depend upon the make and model of your vehicle.

How to check your brake master cylinder at home

It helps to regularly check your master cylinder t home. It’s easy and quick to do so.

Remove the cap of the fluid reservoir and look inside. Be careful not to allow dirt to fall into the reservoir. The level of fluid should be at the full level mark or thereabouts. If the level is fine and you have a problem with the brakes, it could a fault with the cylinder. Close the reservoir quickly so that oxygen and water vapors don’t contaminate the fluid. Finally, check for signs of leakage under the master cylinder.