Surface crazing or cracking on brake discs
The picture above shows a normal cast iron brake disc that exhibits what we call crazing. These are tiny hairline cracks that are extremely small and not of real concern. These are microns deep and are exaggerated by the black brake dust generated under normal driving. This does show that the brake discs have been quite hot and could encourage you to have your discs Pro Cut skimmed which can be performed several times during the life of your brake discs or rotors.
The Pro Cut skim removes only 4-6 thousandths of an inch and does not cause the discs to go below thickness.
There is good logic for this type of “Renovation” of your brake discs rather than replace the discs with new ones for the simple reason that a good USED disc is actually a better performing product than a new one. New discs require lengthy bed in times during which time the disc materials “Settle” and grain structure alignment takes place. Also the Pro-Cut machine is brilliant at taking a minimal skim from your discs WITHOUT REMOVING THEM FROM THE CAR which exposes you to a re-seating process and possible disc distortion and vibration arising.
If your discs show the above crazing continue to use them and/or undergo the Pro Cut skimming and monitor them every 1000-2000 miles visually. If the crazing gets significantly deeper the discs may have to be replaced.
Crazing is caused by the discs working hard, it is not a sign of a poor disc quality but it may be a sign that the brake pads you have fitted are not removing heat from the braking surface adequately. Quality brake pads do this well and cheap pads do not. Cheap pads are made mainly from resins and fillers and do not include the thermally conductive elements included in better products.
A good set of brake pads will always costs between $60 and $150 or UK pounds £50-£100,anything less and you probably have been sold a low grade pad. To select the right QUALITY PADS for your vehicle use this selector chart.