Shuddering brakes can be an alarming way to find out that your vehicle's braking system has a problem. Although not catastrophic in and of itself, this condition can result in reduced stopping power and poor vehicle control in emergency stopping situations. Fortunately, this problem is usually easily addressed, although it can be pricey. Understanding how this problem occurs will help in determining the proper procedure for repair.
Lateral runout is the measurement between two axes that determines how parallel they are with each other. In automotive brake systems, this is the measured difference of the brake rotor axis to the axis of the spindle. If the measurement exceeds factory tolerances, the brake rotor will intermittently contact the brake pads. This causes uneven wear of the rotor, resulting in vibration and shudder when the brakes are applied.
"Warped rotors" is a misnomer. This is an all-encompassing term usually used to describe a condition in which the surface of a brake rotor is no longer even or flat. Rotors do not become warped, but instead become unevenly worn due to several unusual processes, resulting in a situation where the rotor makes intermittent contact with the brake pads. When the brakes are applied, this uneven surface causes the rotor to push back on the brake pads intermittently, causing vibration of the wheels and pulsation at the brake pedal.
Prolonged disuse of a vehicle can allow rust and corrosion to form on brake rotor surfaces. This is more pronounced in areas of the country where salt is used on roads in the winter. After sitting for long periods, this corrosion causes uneven wearing of the rotor surfaces when the brakes are applied. The high points of the rotor then push back against the rotor during braking, causing vibration and shuddering.