In some cases the car driver can feel a pulsation or vibration in the brake pedal every time a car stops, though the brakes seem to work fine.
Car experts say a pulsating brake pedal, which is accompanied by a shuddering or jerky stop during normal braking, usually means a warped rotor or an out-of-round drum - although it can sometimes be caused by loose wheel bearings, a bent axle shaft or loose brake parts. Some pedal feedback and noise is normal during panic stops or when braking on wet or slick surfaces. But there should not be pedal feedback when braking normally on dry roads.
The faces of a disc brake rotor must be parallel (within .0005 inch on most cars) and flat (no more than about .002 to .005 inches of run-out) otherwise it will kick the brake pads in and out when the brakes are applied, producing a pulsation or vibration that can be felt in the brake pedal as the rotor alternately grabs and slips.
One can often see visible warps in a brake rotor. If the rotor has telltale glazed or discoloured patches on its face, it is probably warped. Measuring it with a dial indicator and checking it for flatness with a straight edge will confirm the diagnosis.
Resurfacing the rotor to restore the faces and remove the pulsation. But it will be temporary because of metallurgical changes that take place in the rotor. Resurfacing will restore the surface, but the warps may reappear again in a few thousand miles as the rotor wears. For this reason, some companies recommend replacing warped rotors rather than resurfacing them.
Rotors get warped due to several reasons most common being overtorquing or unevenly torquing the lug nuts with an impact wrench. For this reason, experts recommend using a torque wrench to tighten lug nuts when changing a wheel. There are also special torque-limiting extension sockets called 'torque sticks' that can be safely used with an impact wrench to accurately tighten lug nuts. But a plain impact wrench should never be used for the final tightening of the lug nuts because most provide no control whatsoever over the amount of torque applied to the nuts.
Another reason why rotors get warped is overheating which is the result of severe abuse or dragging brakes.