Low Brake Pedal
A low brake pedal could be caused by a misadjusted brake pedal or contaminated brake fluid. The brake pedal is adjusted with the master cylinder pushrod. The pushrod is usually (almost always) made of two parts and lengthened or shortened by adjusting a nut located on the rod. This adjusted nut is then locked in place with a locking nut located on the same rod. Drum brakes that are out of adjustment will cause a low brake pedal as well.
Contaminated, overheated, or aerated brake fluid will also result in a low brake pedal. This is common and checking the condition of the brake fluid can not be overlooked during diagnosis. Brake fluid is hygroscopic, meaning that it has an affinity to and attracts moisture. If a container of brake fluid is left open it will attract moisture and quickly become contaminated. Always keep the brake fluid container sealed and stored away safely.
Brake fluid is rated by the Department of Transportation, the DOT. They rate the different brake fluids by assigning them a number like DOT3, DOT4, and DOT5. The higher the DOT rating the higher boiling point. The more heat it takes to boil! Moisture in a brake system will lower the boiling point. If moisture is suspected a brake flush with the correct DOT fluid is required. DOT5 brake fluid is silicon based and DOT3 and DOT4 fluids are glycol based. Never mix the two. This will result in a spongy brake pedal and a loss of braking performance.