as long as the rotor is flat, and still within minimum spec, you can successfully swap out pads with no issue - if there are grooves in the rotor at all, this doesn't work well - surfacing is very inexpensive - most machine shops will do it for less than $20 each, even on drilled rotors
the only other thing to consider is that used rotors are thinner, therefore less able to handle high heat transfers - this could come into play if you are driving the car hard
as for bedding them on existing grooves, i had this argument a number of years ago
the very common misconception is in thinking that since a grooved rotor actually has more surface area, that it should be able to stop better - what isn't intuitively understood is that brakes work best when an even layer of deposit is on the rotor, and that this is impossible to maintain with a grooved rotor, because as the pads heat up, the increased surface area of the grooves, act like a heat sink, and change the way the pad heats and lays down the bed, which only happens when the pads are up to temp - the uneven pattern makes for cool spots that work against this - every time you heat up the rotor in this scenario, you tear away some of that bed, and lay down some more in differnt spots - this makes for a very uneven bedding - this is why you get the "juddering" sensation that is often misdiagnosed as warping - the rotor isn't actually warped - the deposits are just uneven, making it pulsate as it goes around
brakes are really very complicated science - race car tuners will tell you that second only to tires, races are won and lost most on brakes - yes, you can get a car to stop, and mixing and matching used and new parts can be done - it's really about how much compromise you are willing to accept in feel, stopping distance, and safety
94 Midnight Metallic Blue Cab Porsche 968 w/deviating cashmere/black interior and WAY too many mods to list - thanks to eric for creating
www.968forums.com
"It isn't nearly as expensive to do it right as it is to do it wrong."
