One of the most common brake-related complaints people have involves spongy pedal feel. Under normal circumstances, the brake pedal should always have a firm, solid feel to it. The further you press down on the pedal, the harder the pedal becomes. If the pedal feels soft and spongy or if it sinks all the way to the floor, there may be a malfunction somewhere that could potentially make your vehicle unsafe to drive. Spongy brakes can be caused by a number of underlying issues that should be taken care of as soon as possible.
Brake Fluid Contamination
Glycol-based brake fluids such as DOT 3, 4 and 5.1 are hygroscopic, meaning they readily absorb moisture the moment they're exposed to air. This attribute prevents moisture from sitting in areas of the brake system where it can turn corrosive and degrade critical components. The downside, however, is that it'll continue to draw moisture from any place it can find it, including porous metal surfaces.
As your brake fluid ages, it could contain water in concentrations of 8 percent or more. Even having just 1 percent water in your brake fluid can significantly lower the brake fluid's boiling point, which in turn degrades your car's braking performance and brake pedal feel.
Checking and changing your brake fluid according to your vehicle manufacturer's recommended service schedule can prevent brake fluid contamination from occurring.
Air in the Brake Lines
Trapped air within the brake lines can also give your brakes a soft, spongy feel. Air can seep into the brake fluid reservoir as fluid levels drop over time, allowing air bubbles to migrate throughout the rest of the brake system. Air can also make its way into the system whenever you open the reservoir to check fluid levels. Trapped air can interfere with the amount of hydraulic pressure needed to move the brake caliper pistons on disc brakes and the wheel cylinder in drum brakes.
Fortunately, you can remove this trapped air by bleeding your brakes. You can have a trained mechanic carry this task out or perform the procedure with a partner's help. Keep in mind that some vehicles may require a scan tool to cycle the anti-lock brake system (ABS) pump during the bleeding process.
Corroded Brake Calipers
Over time, internal and external rust and corrosion can occur on the brake calipers, especially if the vehicle is regularly subjected to salt and road grime. Not only can this cause parts such as the caliper slides to stick and create uneven pad wear, but it can also cause various seals to leak brake fluid, resulting in soft brake pedal feel.
If your brake calipers are corroded to the point of sticking and leaking, you should have them replaced as soon as possible. For good measure, you'll also want to have your brake fluid changed and bled.
Leaking Wheel Cylinder
Commonly found on drum brakes, wheel cylinders perform the same task as the caliper piston – they help push the brake shoes firmly against the inner drum surface whenever you apply the brakes. If you're experiencing spongy brake pedal feel, a leaking wheel cylinder could be among the potential causes.
In most cases, replacing the wheel cylinder takes care of the problem. For good measure, you should have your mechanic inspect the rest of the drum brake system for any other signs of damage or leaks.
Malfunctioning or Worn Master Cylinder
Spongy brake pedal feel can also be caused by a failing master cylinder. Located just behind the brake fluid reservoir on most vehicles, the master cylinder controls the amount of hydraulic pressure delivered throughout the brake system. A leaking, damaged or otherwise worn-out master cylinder can not only make your vehicle's brake pedal feel soft, but you may also experience complete brake failure if it isn't repaired or replaced in time.
If you think you car's brakes feel spongy and might be suffering from one of these problems, contact a company like Big Mechanic soon to have them inspected.