What Causes My Brake Pedal To Sink?

As important as it is for your vehicle to start and go forward, it is even more important that it be able to stop. A brake pedal that feels mushy, spongy, or that slowly sinks to the floor when depressed can be best described as brake pedal sink. If your brake pedal sinks towards the floor when you are stopped, while your foot is on the brake, or does not feel as firm when the brakes are applied, this could indicate you are having some sort of trouble with your brakes.

There are two different kinds of brake systems: disc or drum brakes. Brake pedal sink can differ in each vehicle depending on the type of brake system your vehicle has.

    • Disc brakes are made up of a disk, or rotor, a caliper assembly, brake pads, wheel bearings, and other hardware used to mount brakes to the vehicle. The calipers are connected to the master cylinder via tubes, hoses, and valves that push brake fluid throughout the system.
    • Drum brake systems are made up of hydraulic wheel cylinders, brake shoes, and a drum. When the brake pedal is applied, the curved shoes, equipped with a lining of friction material, are forced by hydraulic wheel cylinders against the inner surface of a rotating brake drum.

Typically, the three most common problems related to brake pedal sink are caused by the master cylinder, a brake fluid leak, or ABS unit leak.

The Master Cylinder is a vital component found in modern vehicle braking systems, as it is the main pump that sends pressurized brake fluid through the brake lines, allowing the brake calipers to squeeze the pads against the rotors. The seals within the cylinder can wear out and form internal leaks due to age, especially if brake fluid is contaminated. Contaminated brake fluid usually appears dark brown or black in color. If the master cylinder needs to be replaced, you may recognize the following symptoms:

    • Vehicle is unable to hold brake pressure as effectively as it should, resulting in brake pedal sink.
    • Noticeable when holding constant pressure against the brake pedal at a stop.
    • Pedal sinks or requires pumping to keep your car from creeping ahead.
    • The brake warning light may NOT illuminate.

Brake fluid is a hydraulic fluid responsible for moving the different components of the vehicle’s braking system. It’s a compressible substance that flows throughout the brake lines, delivering the force, created by the depression of the brake pedal, to each of the rotors on the vehicle. The fluid operates under high pressures and temperatures. Without brake fluid your car would not be able to stop. Symptoms the brake fluid is responsible for brake pedal sink:

    • Brake warning light is on (similar to an exclamation point inside a circle, surrounded by parenthesis).
    • Wet spots are identified around hose or line connections.
    • Fluid leaks from a disc brake caliper or drum wheel cylinder.
    • Possible leak from: hose, brake line, calipers, or wheel cylinders.

Note: If you notice any signs of leaking brake fluid, do not attempt to drive the vehicle, as it is extremely unsafe. Have the vehicle towed to a trusted service center for immediate inspection.

The ABS Systemis an added safety feature that is mandatory in all modern vehicles. The ABS system utilizes electronic sensors to detect the speed of the wheel and rapidly pulse brakes to prevent skidding and can quickly stop the vehicle. The ABS system uses a control module and sensors including the ABS fluid level sensor, which is responsible for identifying the amount of brake fluid in the master cylinders reservoir. The ABS system also operates using hydraulic brake fluid and will not work if the level falls below normal. Vehicles with rear-wheel anti-lock brake systems may experience a similar sinking pedal feeling.

At Sun Auto Service our goal is to keep vehicles moving but we believe it’s equally important that the vehicle be able to stop. If you notice any issues with your car’s brakes from a seemingly minor squeak, brake pedal sink, or a vibration felt while braking, bring it to the experts at Sun Auto Service. Any sort of brake issue should not be put off! Your safety is our number one priority which is why we offer free visual brake inspections. Plus, as part of the Sun Auto Service oil change, we include this complimentary service as part of the multi-point inspection. If our technicians identify any trouble with your brakes, you’ll be pleased with our same-day service (in most cases) ensuring you’ll be back on the road with very little interruption to your busy life. With so many locations throughout the Southwest, there’s always a location near you.