There are many words that describe brake problems, including those like "spongy," "soggy," and "squishy." Your brake pedal should always feel firm beneath your feet, with no soft or spongy response when you push on it. If you press the brake pedal and you get some soft resistance or feel as though you're stepping on a large sponge, it's a sign of a brake system problem. Here are the most common causes of these issues.
Damaged Brake Lines
Brake lines are usually made from steel tubing or something similar. Over time, that tubing can rust. This is especially true if you live in an area that's along the coastline, because moist salt air can encourage rust. It's also common in northern regions, because salt is often used on the roads in the winter. The rust causes the brake lines to thin and crack.
Cracks and holes in the brake lines lead to reduced hydraulic pressure in the braking system. This causes a soft brake pedal. Inspect your brake lines for any indication of rust. If they are visibly damaged, it's time to have them replaced. You'll find the brake lines under the car, most frequently running along the frame rail on one side or the other of the car body.
Air in the Lines
When you get air in a hydraulic system, it can disrupt the function of the system. Air interferes with the hydraulic pressure levels necessary to maintain solid brakes. If you suspect that you might have air in the brake lines, your mechanic can bleed the brakes to purge any air bubbles.
If the calipers on your disc brakes are damaged, it can make the brake pedal feel soft and spongy. Corrosion can build up inside a caliper over time, which can cause brake fluid leaks from the piston inside the caliper. If this happens, you'll need to have your calipers replaced. If you can see brake fluid seeping around the brakes but there's no visible damage to the lines, it may be a leaky caliper.
Bad Wheel Cylinders
Like calipers, wheel cylinders can corrode internally. Found as part of drum brakes, the wheel cylinders have internal pistons that can allow brake fluid to seep past if worn out or corroded. For this reason, it's important to have your wheel cylinders inspected regularly as part of your routine safety inspections.
Brake problems are not something you should dismiss. Since your brakes are a vital part of safe vehicle operation, acknowledging and addressing a malfunctioning brake pedal (no matter which word best describes it) is important. Take your car in for brake service if you suspect any problems.