7 Symptoms of a Bad Brake Master Cylinder

Covered In This Article

Symptoms of a Bad Brake Master Cylinder – The brake master cylinder drives pressure generated by the brake pedal to the braking mechanism on your car wheels.

The brake master cylinder is a very important component in your car’s braking system and it is a fundamental component of your car’s braking system. The component is a hydraulic pump that supplies brake fluid to the brake circuit to convert the pressure on the brake pedal to hydraulic pressure.

When you apply pressure on your brake, the force pushes a piston through the brake cylinder and converts the force into hydraulic pressure. In manual brakes, the brake master cylinder is attached to the firewall and linked to the brake pedal while in power-assisted brakes, it is applied to the brake booster which supplies more power to the braking system.

How Does a Brake Master Cylinder Work?

The brake master cylinder turns pedal pressure into hydraulic pressure and this is done by supplying the brake pedal with brake fluid. 

Two master cylinders share a cylinder bore which allows the cylinder assembly to control different hydraulic circuits. The separate circuits control the brakes for a pair of wheels.

The circuit can be configured in a way that if one brake circuit fails, the other circuit can control the pair of wheels and stop the vehicle. 

Here are two ways in which a circuit can be configured:

  • front or rear configuration (two front or two rear). 
  • diagonal configuration (left-front / right-rear or right-front / left-rear).

A component called the master cylinder reservoir is placed on top of the master cylinder and is filled with fluid to prevent air from penetrating the braking system. 

In most vehicles, a proportioning valve connects the master cylinder to the rest of the brake system.

Symptoms of a bad brake master cylinder
Symptoms of Brake Master Cylinder

Symptoms of a Bad Brake Master Cylinder

A warning light illuminates on the dashboard

When the brake warning light illuminates the dashboard, it is an indicator that there is a problem with your brake master cylinder or other components of the brake system. 

If the brake master cylinder is leaking fluid, the ABS light will come on. Also, if the brake system sensor detects a drop in the temperature of the brake fluid which is usually a result of a bad brake master cylinder, the warning light will come up on the dashboard.

Leaking brake fluid

If your master cylinder is leaking brake fluid then there is a problem with it. 

Leaking brake fluid will cause a low brake fluid level which will limit your ability to slow down your vehicle. Low brake fluid will reduce the hydraulic pressure required to slow down a vehicle. 

If you are facing this, you need to replace your brake master cylinder.

Contaminated brake fluid

There is certainly a problem with your brake master cylinder if your brake fluid gets contaminated easily. 

There are rubber seals on the brake master cylinder designed to hold fluids and brake pressure effectively. 

These seals will, however, break down over time if used continuously and when this happens the brake pedal will get mushy or spongy and the brake fluid will be contaminated.  

Sinking brake pedal

A bad brake master cylinder can also cause your brake pedal to sink. 

In this case, the brake pedal will sink into the floor after you remove your leg from it. 

Every pressure from the braking system is generated by the master cylinder and if the cylinder is bad, this pressure will not be evenly distributed which will affect your brake pedal.

Spongy or soft brake pedal

Air in the brake lines or a bad master cylinder is the main reason your brake pedal will feel soft or spongy when you press your leg on it. 

The master cylinder is made of rubber seals which help to keep the brake fluid inside. If worn out, the brake fluid will leak from inside causing the pedal to be spongy.

Uneven brake pad wear

The master cylinder is made up of two different circuits that circulate brake fluid to the wheels in pairs to prevent a total loss of braking when one side is affected. 

Failure of one of the piston seals of a master brake cylinder or brake line leak will lead to uneven brake pad wear. This is because it will cause one brake circuit to fail and if only two wheels out of the four can apply the brake, there will be uneven brake pad wear over time. 

For instance, the front right side and left rear side could be worn out than the front left side and right rear side. 

Bad brake bias

The two brake circuits usually control one front wheel and the opposite rear wheel.

If one side of this circuit fails as a result of a failing master cylinder, your vehicle will pull to one side while braking, especially when you press the brake hard.

Causes of Brake Master Cylinder Failure

Several factors can cause the brake master cylinder to fail. 

One of such is worn-out rubber seals. The rubber seals help to store fluid and if they get damaged, there will be an internal leak. 

Other factors that cause brake master cylinder failure include:

  • Overheating brake pads. 
  • Leaking hydraulic fluid. 
  • Overloading your vehicle. 
  • Driving through mud or deep water. 
  • Loss of hydraulic brake fluid pressure.

Another very common cause of brake master failure is negligence by the vehicle owner. Many people neglect their automobiles and fail to inspect certain components even when there are some subtle symptoms of failure.

How to Quickly Spot a Bad Brake Master Cylinder

You can know a bad brake master cylinder when you notice certain signs such as unusual brake pedal behavior, contaminated brake fluid, brake fluid leak, and uneven wear in the brake pads.

However, you can closely check your brake master cylinder to spot a problem using these easy steps. 

  1. Open the brake fluid reservoir on top of the master cylinder. 
  2. Take a close look at the lid to see if it is broken or worn out.
  3. Look inside the master cylinder. 
  4. Use a flashlight to look for junk or wetness inside the cylinder. Doing this will enable you to know if the master cylinder is leaking or if there is any other problem with the brake master cylinder.
  5. Close back the master cylinder carefully to prevent dirt from entering.

How to Evaluate the Condition of the Brake Master Cylinder

You can access the condition and diagnose a problem with your brake master cylinder by taking the following steps. 

Step 1. Check the brake master cylinder for leaks

A leaking master cylinder is a common sign of a failing brake master cylinder. 

The master cylinder can leak around the seals that connect it to the reservoir which stores fluid or in the plunger that connects it to the brake booster. 

Whatever the case may be, it isn’t safe to drive your car with a leaking brake master cylinder. A problem with the brake master cylinder always demands urgent attention and the worn-out parts should be replaced as soon as possible.

Step 2. Check the level and condition of brake fluid

Low or dirty brake fluid will affect the functioning of the braking system. 

The brake fluid in a normal situation is usually clear but when it is dirty or has debris in it, it will turn dark and will affect the brakes of your vehicle. 

Contaminated fluid will clog the cylinder and it will be difficult to dispense fluid from the reservoir down to the brake system.

Step 3. Check the brake booster for rust, dampness, and rotting

The seal between the master cylinder might be leaking fluid inside or outside the booster and it might be difficult to see it. You will need to remove the master cylinder and carefully inspect the inside for leaks. 

Brake fluid is highly corrosive and when it leaks on the brake booster, it will corrode the paint and cause it to rust or rot.

How Master Cylinder Influences Braking Performance

The master cylinder bore diameter influences braking performance. 

If the diameter of the cylinder is changed, it will affect how the brake feels on your leg when you try using it and it will also affect the brake pressure that is applied.

If the diameter of the cylinder bore is too small, it will create a soft brake pedal that requires less effort to press the pedal or a long stroke that requires that the brake pedal be pressed down completely to generate braking pressure.

Due to low resistance, you’ll have to press the brakes farther than usual for it to work. This is not a good scenario as it can become very difficult to use the brake when needed.

If the diameter of the cylinder bore is too large, it will cause a hard brake pedal which requires more effort to press the pedal, or a short-stroke where the brake pedal doesn’t have to be pressed too far to generate braking pressure. 

In this case, your brakes become high resistance which will cause a jumpy car as you will have to tap the brakes too hard for it to work.

Brake Master Cylinder Replacement Cost

The average cost of replacing a brake master cylinder is usually between $320 and $700 with labor costing more. 

The cost of labor is about $230 to $300 while the part to be replaced costs $100 to $210. The cost of replacement varies based on the model and make of your vehicle. 

For example, the cost of replacing the brake master cylinder of a Chevrolet Silverado is between $300 to $500, a Ford Focus would cost $400-$750, Toyota Camry is between $310-$530 while a Honda Civic will cost $230 to $475.

How to Fix A Bad Brake Master Cylinder

If you are conversant with some car components and your brake master cylinder is damaged, you may want to try fixing the vehicle on your own. 

Here are steps on how to correctly fix a brake master cylinder

Step 1. Inspect and take note of the position and condition of the brake lines

Check the brake lines that lead down to the flex hoses to ensure that there is no rot in them.

Swollen flex hoses will restrict the flow of brake fluid to the brakes. While inspecting the brake master cylinder, if the brake lines are rusted or rotten and you loosen the fittings from the cylinder you could twist or damage the lines after installing a new master cylinder.

Step 2. Inspect the condition and function of the bleeder screw

When you inspect the bleeder screw on the brake caliper, ensure they can open up, if not, you’ll be faced with a situation where you can’t bring out your bleeder screw which will restrict you from getting air out of the master cylinder after servicing the cylinder.

If the bleeder screw is broken you will need to replace the entire caliper. However, if it is rusted or rotted you can replace the bleeder screw without replacing the calipers. 

Step 3. Assess the condition of the brake pads

Ensure that there is enough brake pad material and the brakes are in a good working condition.

Step 4. Test the brake calipers

You do this by testing the piston with a rewind tool to ensure it is still in good shape.

Step 5. Replace a damaged brake master cylinder after inspecting other components of the braking system

After inspecting and assessing all other components of the braking system, you replace the faulty master cylinder with a new one. This requires loosening the brake line fittings and removing the bolts from the master cylinder.

Step 6. Check the brake master cylinder for leakage

Check and confirm that there is no fluid outside the master cylinder. If the cylinder is leaking, it will damage the booster.

Step 7. Check the brake booster for damage

Inspect the body of the booster to ensure the paint is not deteriorating. Also, inspect the interior to ensure the fluid is not leaking internally. If the booster is sealed and fluid has not leaked inside, brush off flaking paints from the exterior part of the booster.

Step 8. After repair, bleed the brake system and test drive the car

After repairing the brake master cylinder, what needs to be done is to bleed the brake system to remove the air trapped inside. Add new fluid to the brake system, get a specific manufacturers’ bleeding sequence and take your car for a test drive.

Frequently Asked Questions About Brake Master Cylinder

What are the effects of driving with a bad brake master cylinder?

It is very unsafe to drive with a bad brake master cylinder. The brake master cylinder is a very essential component of the vehicle and driving with a bad brake master implies that you will have difficulties in braking. At this point, your brake becomes less functional. You can have a spongy brake pedal or one that sinks completely to the floor. This will make braking difficult and can lead to ghastly road accidents.

Can a brake master cylinder fail without leaking?

Yes! Your brake master cylinder can fail without leaking. If the seals of the master cylinder are damaged, it will not have the ability to hold fluid and brake pressure effectively which will cause the brake to be spongy.

Will a bad master cylinder cause brakes to stick?

Yes! A bad brake master cylinder can cause your brake to stick. When the brake pedal is pressed, the hydraulic pressure in the brake system increases and it forces the calipers to grab the rotor or shoes to engage the brake drums. The brake system can fail while your foot is on the brake and when this happens, the system will remain locked in an “on” condition leading to a sticking brake.

What will happen if my brake master cylinder leaks internally?

A master cylinder with an internal leak will not be able to acquire the necessary hydraulic pressure. The brake pedal will feel spongy and sink gradually. Instead of the fluid pushing on the calipers, it leaks backward around the rubber seal that protects the piston. If your brake master cylinder is leaking internally, you will experience a soft, squishy feeling when you press down the pedal. Again, fluid would be dripping down the brake booster which will dissolve paint quickly and leave a bubbled paint.

How can I prevent early brake master cylinder failure?

You can prevent early brake master cylinder failure by handling your brakes with care and avoiding rough driving. Aggressive braking builds up a lot of pressure inside the hydraulic system which can lead to brake master cylinder failure.

Prolonged or rough driving can also build up pressure in the hydraulic system, the brake fluid will get hot and become vapor. This vapor tries to pass through the piston seals and this will lead to damage to the seals which can cause the brake fluid to leak from the cylinder.

Some new brake fluids have additives that keep the seal conditioned. With time, this brake fluid will get contaminated and lose some of these additives. The old and contaminated fluid makes the seals wear off quicker. In this case, it is important to change your brake fluid periodically.

Can I still brake if my master cylinder is leaking?

It is unsafe to drive with a leaking master cylinder because when the brake fluid has leaked out leaving the brake system with insufficient fluid, it will cause the brake pedal to behave abnormally. Since all the pressure in the braking system is generated by the master cylinder, if it is bad, it will not distribute pressure properly which will cause the pedal to sink, feel spongy, and have high or low resistance. If any of this happens, you will not be able to brake properly which is a very risky situation

Do I need to fix my brake master cylinder right away?

As far as there is a problem with the brake master cylinder, it needs to be repaired or replaced as soon as possible. Any sign of leaking fluid or damaged seals requires that you repair or possibly replace the master cylinder. Problems with the brake master cylinder can cause brake failure which can be a very dangerous situation. Due to this, it is very essential to fix your brake master cylinder once there is a problem with it.

Reply