5 Signs of a Bad Brake Master Cylinder (and Replacement Cost)
Our vehicles must have working brakes to keep occupants safe, but the braking system is made up of so many moving parts that they can fail.
The brake master cylinder is one of the main components of the system, so when it fails, there are serious consequences to follow.
However, a brake master cylinder in poor condition causes strange symptoms that are not always easy to diagnose. Here are some signs to look for:
The most common symptom of a bad brake master cylinder is a spongy or sinking brake pedal. You may also notice a decrease in braking ability or, in the worst case, no brakes at all. If you see brake fluid on the floor, that could also be a sign of a bad brake master cylinder.
Here is a more detailed list of the most common symptoms of a bad brake master cylinder:
Symptoms of a Bad Brake Master Cylinder
At first, you will probably notice that the brake pedal acts unusual. The master cylinder generates all the pressure necessary for braking.
So if there is a problem with pressure distribution or sealing, you will notice it in the pedal.
As cylinder seals continue to wear, leaks can also occur. This is part of the reason why the brake master cylinder causes a boiled or spongy pedal. You could even make it travel to the ground.
Unfortunately, this symptom alone will not tell you that the master cylinder is bad. A spongy pedal most often means there is air in the brake lines. Your car may only need a brake fluid change.
2. Inconsistent brakes
When the master cylinder begins to fail, the brakes may act erratically. At first the brakes may work normally, and the next second you may completely lose stopping power.
This is, of course, a very serious problem, as it becomes even more dangerous when you don’t know when the brakes are working as they should.
Additionally, the pedal may feel firm one second and head toward the floor the next.
3. Reduced braking capacity
When the master cylinder begins to fail, it can cause the brakes to release only in the front or rear. When this happens, you will notice a significant drop in braking power.
As you prepare to stop, you don’t have that extra time and could end up in an accident.
Other faulty parts of the brake system can cause this same symptom. You may have air in your brake lines or old, worn fluid. These symptoms also occur if you have a burned brake line or hose.
4. No brakes
In more severe cases, the brakes may not work at all. Although it doesn’t happen often, it is possible.
The master cylinder works like a hydraulic pump, constantly pressuring the brake lines when you touch the pedal. With this design, it is much more common to lose brakes in the front or rear, but not both.
However, you could end up with no brakes when the master cylinder fails.
5. Liquid leak
Inspect the system for brake fluid leaks. If you notice brake fluid leaking from the back of the master cylinder along the brake booster or firewall, you have a problem.
You can even see the brake fluid running down the firewall inside the cabin. Eventually, this leak will cause a lack of brake fluid in the system, which will reduce your stopping power.
As the fluid leaks out, you’ll also notice the spongy pedal we talked about earlier. Although it may regain some firmness when you pump it, it won’t last long until a repair is done.
RELATED: 5 Symptoms of a Brake Fluid Leak
The function of a brake master cylinder
The master cylinder acts as a hydraulic pump. It is responsible for supplying brake fluid to the brake circuit, where it converts brake pedal pressure into braking power.
Think of the master cylinder as a syringe. Every time pressure is applied, fluid flows out of this cylinder towards the brakes.
Modern master cylinders contain two chambers, each of which operates a set of wheels. Because of this design, you should only lose the front or rear brakes if they fail, usually not both.
There is a reservoir built into the master cylinder that contains the brake fluid. When the brakes are applied, fluid flows through the brake lines, causing the brakes to work.
Once the brake pedal is released, the fluid returns to the reservoir, releasing the braking system and allowing the wheel to move again.
Brake Master Cylinder Location
The brake master cylinder is located below the brake fluid reservoir. To find it, look under the hood on the driver’s side of the vehicle.
It is usually located on the firewall. You’ll notice this because it has two or four brake lines attached to the main body. It is also connected to the brake fluid reservoir with a small wiring connector.
Brake Master Cylinder Replacement Cost
The cost to replace the brake master cylinder ranges from $250 to $400. You have two options when replacing the master cylinder. You can choose a rebuilt cylinder or buy a new one.
Because of the importance of the brake system to your safety, it is often recommended to get a new master cylinder. A new master cylinder costs between $35 and $75, depending on the model of your car. The rest of the expense is labor at your local store.
If you plan to do it yourself, you don’t need any specialized tools. However, you’ll want to factor in an extra $4 for brake fluid and about $10 for the necessary bleed kit.
