7 Symptoms of a Bad Master Cylinder
Have you ever pressed down on your brake pedal expecting your usual confident deceleration only to find that the pedal feels spongy, a warning light illuminates on your dashboard, or a lack of stopping power? These are all big signs that your master cylinder may be failing.
If you ignore these and other symptoms of a bad master cylinder, you are putting yourself and others at grave risk. So, read on to find out what the problem is and how much it could cost to repair.
The Importance of the Master Cylinder
The master brake cylinder is the heart of your vehicle’s hydraulic braking system. This vital component converts the mechanical force of the brake pedal into hydraulic pressure that activates the brake calipers and pads.
The master cylinder houses a reservoir that stores brake fluid. When you press the brake pedal, it activates a pushrod inside the master cylinder. The pushrod then pushes two pistons outward, pressurizing the brake fluid in the reservoir.
This pressurized fluid flows through brake lines and hoses to each wheel cylinder and caliper assembly. In the wheel cylinder of each wheel, pressurized brake fluid exerts equal force on both brake pads, forcing them against the surface of the rotor, which may slow or stop the vehicle.
The harder you press the brake pedal, the more force is exerted on the piston in the master cylinder, and the more pressure is sent to the brake caliper to stop the wheel from turning.
Symptoms of a Bad Master Cylinder
When your master cylinder starts to fail (or has already stopped working), you may experience one or more of the following symptoms:
1) Brake Warning Light
The first symptom you’ll likely notice is when the brake warning light on your dashboard comes on. This indicates a problem with the brake system, but does not necessarily mean the master cylinder is defective.
However, if the brake system sensors detect a loss of brake fluid pressure, it may be due to a faulty master cylinder, which will turn on the warning light. If the ABS light comes on, the master cylinder may be the culprit, especially if the master cylinder is leaking.
2) Leaking Brake Fluid
The master cylinder requires a certain level of brake fluid to generate the hydraulic pressure needed to slow the vehicle. If your master cylinder is leaking brake fluid or you have an unsecured container holding the fluid on the cylinder, you can be pretty sure that your brake fluid level is low.
This means that you can no longer slow your vehicle down as fast, which calls for a master cylinder replacement.
3) Spongy brake pedal
If your brake pedal feels spongy when you press it with your foot, this automatically indicates that there may be an issue with your master cylinder.
The cylinder has a rubber seal built into it that keeps the brake fluid inside. When these rubber seals become worn or damaged, internal brake fluid leakage can occur. This results in a spongy feel on the brake pedal.
4) Brake Fluid Contamination
Another problem that can result from worn rubber seals is brake fluid contamination. Not only do the seals prevent brake fluid from leaking, they also keep dirt and debris from getting into the brake fluid.
When this happens, you experience less braking pressure when you press the brake pedal. You will find yourself pressing harder on the pedal just to slow your car down like you normally would.
5) Sinking Brake Pedal
When all of these other symptoms occur, you will notice that when you release your foot from the brake pedal, the pedal doesn’t return all the way. Instead, it slowly sinks to the ground. This can be dangerous for real driving, so at this point you should have your master cylinder repaired immediately.
6) Bad Brake Bias
Most often, brake master cylinders contain two separate circuits that distribute brake fluid to a pair of wheels. This is intended to prevent a complete loss of braking effect if there is a leak on one side of the system.
Often these circuits control one front wheel and the rear wheel on the opposite side. For example, the left front wheel and right rear wheel might share a circuit, and the right front wheel and left rear wheel might share a separate circuit.
If a circuit fails, you may notice your vehicle pulling to one side when braking. This is most noticeable when braking very hard, as the front brakes have more force to stop the vehicle than the rear brakes.
7) Uneven brake pad wear
If only two of the four wheels can operate the brakes, a defect in the brake circuit causes uneven brake pad wear. For example, the front right and rear left wear more than the front left and rear right.
A brake circuit can fail if any of the master cylinder piston seals are defective or there is a leak in the brake line. If you notice uneven braking, uneven brake pad wear, or your car pulling to one side when you apply the brakes, you may have a bad master cylinder.
