feel as smooth as the rest of the rotor but the coefficient of friction for it is different than the surrounding metal. It will appear as round or so discolored patches in the rotor.. Through impurities in the alloy, and excessive heat in places causing a wierd heat treat to spots of the metal you can develop these areas...Remachining the rotor will temporarily get rid of this but it will return soon since the affected areas is actually harder than the material around it... On some cars you can actually squeeze the pads together with your hand while spinning the rotor and feel these areas where the pads slip and grab even though visually it doesn't look like much. Thats one condition, another is a warped rotor as the others have mentioned which is easily detected with a dial indicator . Also tires that have defects in the roundness will sometimes cause a similar sensation too.



Quote Originally Posted by Gene in NC
Brake disk condition that would cause heavy pulsing/hammering on braking? Buddy claims that hammering on light braking that can be damped by HARD braking may be caused by brakes instead of control arms. This leaves me with a problem.

What am I looking for in rotor condition that might cause such a problem?