Racing: Technical Advice
AVOIDING BRAKE JUDDER
Brake judder is caused by an uneven buildup of pad material on the friction surface of the disc. This can occur with improper or incomplete bed-in, or when changing between incompatible pad materials on the same disc. During bed-in some judder can occur for the first 5 to 10 laps or until the discs and pads are sufficiently warmed and can vary from a barely noticeable vibration to a violent shake.
Uneven pad transfer can also be caused by Imprinting, which is staying too long on the pedal when the car is standing still, but the brakes are hot. Small particles of the friction material can bond into the disc surface, or potentially pull the transferred layer out of the disc surface.
BIGGER VS. SMALLER PAD
A bigger pad doesn’t mean a bigger stopping power, but the greater heat capacity of the larger pad can improve modulation,
wear rate and lead to more consistent performance.
PAD FADE VS. BRAKE FLUID FADE
If the temperature between pad and disc gets too high, the pad starts gasses out, building up an air cushion between pad and disc. The pedal remains stiff, but the stopping power is reduced. Solutions are an improved cooling, change to a higher temp range pad material or a higher mass brake disc.
If there is too much energy being transferred to the caliper and fluid, it can boil the fluid. These gas bubbles being compressible, the pedal travel increases and becomes “spongy” with poor modulation. (This is a gradual process with advanced warning.) Solutions include: Changing brake fluid to one with a higher boiling point, using a different pad compound with better heat transfer properties, or improving the cooling to prevent the fluid from boiling.
The importance of keeping fresh brake fluid in the system and regular bleeding cannot be overstressed.
WATCH THE TEMPS!
We recommend monitoring the peak brake disc temps with a thermal paint kit, the most common of which is the 3 color (Green, Orange, Red) system.
Ideally, the green paint (430°C / 806°F) should be completely oxidized (turns white), the orange paint (560°C / 1040°F) should be symmetrically beginning to oxidize and the red paint (610°C / 1130°F) should be un-touched or change only slightly.
Caliper temps can be monitored with temperature strips to assist with pinpointing heat-related system issues.