Quick Tech With Mar­lan Davis

Hot Rod - - Contents -

We’ve pre­vi­ously dis­cussed the pos­si­ble pros and cons of cross-drilled brake ro­tors. The sup­posed up­side of cross-drilling was pre­vent­ing brake fade by im­prov­ing gas vent­ing of tra­di­tional disc brake pad com­pounds when they be­gin to break down at ex­treme tem­per­a­tures, plus im­proved “bite” due to the nu­mer­ous small holes im­prov­ing the co­ef­fi­cient of fric­tion. How­ever, the big down­side, par­tic­u­larly for long-term street use, was the pos­si­bil­ity of mi­cro­c­rack for­ma­tion that can re­sult in cat­a­strophic ro­tor fail­ure.

For­tu­nately, there’s a way to ob­tain most of cross-drilling’s ben­e­fits with­out the danger of cracks: Slot the ro­tor face in­stead. Adding slots or grooves im­proves brake bite and en­sures that as the pad fric­tion ma­te­rial wears, de­bris par­ti­cles are cleared away from the pad face and ro­tor. The slots may also help deglaze the pads.

Slots may be ma­chined into the ro­tor ei­ther as a se­ries of straight lines at an angle not per­pen­dic­u­lar to the ro­tor ra­dius, or as a se­ries of curved lines. Grooves are di­rec­tional; with the ro­tor mounted, they should sweep rear­ward at the ro­tor’s outer edge. The groove should not ex­tend all the way to the disc face in­ner di­am­e­ter.

hHOTROD.COM/ Mar­lan-Davis

Sum­mit Rac­ing [ This StopTech ro­tor fits the front driver-side on many 1999–2005 F-250/F-350 Ford trucks. Be­sides the slots, it also has a cryo­genic treat­ment for greater strength dur­ing re­peated heat cy­cling as well as re­sis­tance to in­ter­nal ox­i­da­tion and warp­ing. Sum­mit Rac­ing sells it for $153.

TEN Ar­chives [ Ma­chin­ing slots into the disc brake ro­tor face pro­vides most of the ben­e­fits of cross-drilled brake ro­tors with­out the danger of crack­ing. As shown here, the slots should sweep to­ward the rear in the as-mounted po­si­tion, and not ex­tend all the way to­wards the disc’s in­ner edge.

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