DRILLED AND SLOT­TED VS. SLOT-ONLY RO­TORS

Hot Rod - - High-tech Braking Systems -

When larger-di­am­e­ter and thicker ro­tors were in­tro­duced to the car-buy­ing pub­lic in the early 1980s via the C4 Corvette and some im­ports, street-com­pat­i­ble pad-for­mu­la­tion tech­nol­ogy lagged.

As a re­sult, pad out­gassing (the pad boil­ing off the resins and binders used to hold the fric­tion ma­te­ri­als to­gether) be­came a sig­nif­i­cant is­sue. You’ll know you have brake fade to pad over­heat­ing when the brake pedal stays hard, but the car won’t stop. If the pedal goes soft, you’ve boiled the fluid.

The an­swer was drilled ro­tors, which gave the gases a ven­ti­la­tion path. Slots al­low the ro­tor to ac­tively clean con­tam­i­nants off the pad face, keep­ing the best el­e­ments of the fric­tion ma­te­rial in use. As a re­sult, drilled and slot­ted ro­tors—along with zinc plat­ing to elim­i­nate ox­i­diza­tion from the un­scrubbed parts of the ro­tor—as in­tro­duced by

Baer Brakes in the 1990s be­came the de­fault stan­dard for high-per­for­mance brakes. You can see this to­day, as even the car­bon-ce­ramic brakes on Fer­raris and Corvettes are drilled. In the last five years, pad tech­nol­ogy has evolved dra­mat­i­cally, and as a re­sult, prop­erly se­lected, high-qual­ity pads don’t have out­gassing is­sues. In­stead, the ad­di­tional heat gen­er­ated can cause ra­dial cracks at the drilled holes, es­pe­cially with big-power, heavy drag cars or fre­quently used track-day cars. If the cracks are fin­ger­nail-width-thick or thicker, the ro­tor should be re­placed. For these ap­pli­ca­tions, slot-only ro­tors are rec­om­mended. For pure road-rac­ing ap­pli­ca­tions with no street driv­ing, some rac­ers will use a plain ro­tor with no zinc plat­ing to speed up ro­tor sea­son­ing and pad bed­ding. Talk to your brake provider’s tech sup­port to get the right an­swer for your spe­cific ap­pli­ca­tion.

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