Cross-drilling is only for looks. On race cars, it reduces weight, but on trucks, it only makes the brakes run hotter because it removes thermal mass. Slotting was originally done to deglaze, and drilling to release gasses generated by organic lining material. But modern pads are cured of these gasses during manufacture, so drilling & slotting are unnecessary. For more info, consult the Wilwood FAQ. If the link doesn't work, here's what it said:

"Why are some rotors drilled or slotted?
Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.
Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value."

Here's a more-thorough article:
http://automotivethinker.com/brakes-2/rotors-blank-vs-cross-drilled-vs-slotted-and-warping/

Before buying craptasmic brakes or other common parts, check for coupons & service offers from Ford.

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Owner caption January 2006 · Photo 1129 of 5000