Brake pedal is soft / sinks
To check for brake problems, you step on the pedal and press it down while paying attention to how the pedal feels under your foot and evaluating the sensation.
The following steps tell you what to feel for:
Start your engine, but keep it in Park with the parking brake on. (If your vehicle doesn’t have power brakes, it’s okay to do this check with the engine off.) With the vehicle at rest, apply steady pressure to the brake pedal.
Does it feel spongy? If so, you probably have air in your brake lines. Correcting this problem isn’t difficult; unless your brakes have ABS or other sophisticated brake systems, you can probably do the job yourself with the help of a friend.
Does the pedal stay firm when you continue applying pressure, or does it seem to sink slowly to the floor? If the pedal sinks, your master cylinder may be defective, and that’s unsafe.
Release the parking brake and drive around the block, stopping every now and then.
Notice how much effort is required to bring your vehicle to a stop. With power brakes, the pedal should stop 1 to 1-1⁄2 inches from the floor. (If you don’t have power brakes, the pedal should stop more than 3 inches from the floor.)
If your vehicle has power brakes and stopping seems to take excessive effort, you may need to have the power booster replaced.
If you feel that your brakes are low, pump the brake pedal a couple of times as you drive around.
If pumping the pedal makes the car stop when the pedal’s higher up, either a brake adjustment is in order or you need more brake fluid.
If the level of brake fluid in the master cylinder is low, buy the proper brake fluid for your vehicle and add fluid to the “Full” line on your master cylinder. Check the fluid level in the cylinder again in a few days.
If you find that you’re not low on fluid, drive carefully to a service facility and ask them to remedy the situation. When they’ve worked their magic, the pedal shouldn’t travel down as far before your vehicle stops.
Disc brakes self-adjust and should never need adjusting. Drum brakes also have self-adjusting devices that should keep the drum brakes properly adjusted. If any of the self-adjuster components on drum brakes stick or break, the drum brakes won’t adjust as they wear out, resulting in a low pedal.