There are places that will cross drill existing rotors, but in general it is a bad idea. Rotors must be heat treated after manufacture in order to provide the necessary properties. Drilling them after heat treating negates the efects of the heat treating process. If they are not subsequently heat treated again, they will be subject to warping, cracking or actual shattering during use.

I would recommend only purchasing new rotors that have been drilled/slotted and then heat treated - and stick with a reliable name brand like Brembo. This is not an area that you want to take chances with.

Drilled rotors provide many benefits including improved cooling, a place for hot gasses from pads during severe use to escape permitting the pads to fully contact the rotor surface rather than floating on the hot gas, and if also slotted, the rotor is much more effective in the rain as the slots will wipe the water from the pads permitting braking to start in less than a full wheel revolution.

Control is also better with drilled rotors - it is easier to modulate the brakes for maximum braking efectiveness without lockup or activation of the ABS - and it is true that good threshhold braking techniques result in shorter stopping distances than ABS is capable of except in the case of rapidly changing surface conditions.

The one drawback is that drilled rotors cause some additional noise on braking - usually only noticeable on heavy braking - not loud or objectionable, but definitely identifiable.

Regards the discussion on the rusted rotors. Be careful with vented rotors that are badly rusted. If the friction surfaces are badly pitted, it is also likely that the interior surfaces (inside the vents) may also have deep pits that effectively reduces the thickness of the rotor, although the outside measurements may still be within specs.

Steve Seekins
sseekins@kryten.atinc.com
90 745 turbo+ w/std tranny
86 745 GL (two sunroofs)
83 242 Turbo, Group A (flathood)
79 242GT (w/83 TI motor and lots of goodies)

Volvo Club of America