Answered by the editors of BRAKE & FRONT END

1. What causes runout?

Rotor runout can be caused by several things: variations in manufacturing tolerances, sloppy resurfacing procedures, a buildup of rust and corrosion between the rotor, hub and wheel, and uneven torque on the lug nuts.

2. What else can cause pulsation problems besides the rotors?

Loose wheel bearings will cause the rotor to tilt in the caliper when a load or side thrust is placed on the bearings. Disc brake pistons require lots of fluid volume and pressure to push the pad against the rotor. If loosely adjusted wheel bearings force the pistons into the caliper, the result will be a low or spongy brake pedal.

3. What exactly is "pulsation" and how does it relate to "warping?"

If a vehicle equipped with floating or sliding calipers has a slider problem which prevents the caliper housing from moving, runout can cause pulsation. The caliper piston will move in and out as the rotor rotates resulting in fluid movement and pedal pulsation. Likewise, fixed caliper vehicles are sensitive to runout induced pedal pulsations. Fixed calipers have pistons on both sides of the rotor due to the stationary caliper housing. Excessive runout will cause piston movement and can result in pedal pulsation due to the runout.

4. What else can cause customers to think their rotors are warped?

Brake roughness is the other component to the equation and it is often misinterpreted and misdia...