Originally Posted by ArloS
What would happen if I just put new pads on slightly scored rotors that can't be machined? Would the world explode? I'm not a brake expert by any means, but I'm EXTREMELY practical. Any advice from the forum?
As some other posts highlighted, there are a couple of other considerations.
But, the big question is: why can't they be machined? Are they too thin, or are they too warped (or combination)?
Setting aside those concerns, the scoring is a combination of raised and lowered 'rings' in your rotor (that matched your break pads). New break pads would be flat - so you would (initally) have less contact between rotor and break pad, therefore less braking power (at the same depression point on the pedal). You would need to push a bit harder on the pedal to get the same braking effect. How much, I can't say - depends on the amount & depth of the scoring - it may not even be noticable.
The effect of this is to concentrate the forces of the braking - same braking demand on less surface area.. The good point is that both the pad and rotor will wear at the contact points and this will tend to smooth things out, so you have less / smoother scoring. The bad point is that this will also concentrate the heat that is generated during the braking. This cause bad things - warping, 'burning' the pads on those groves, etc. to happen. Of course, these are extreme cases, and I'm mentioning them only to scare you.
What you may notice is a bit less stopping power, 'throbbing' in the break pedal, uneven stopping, pulling to one side, and squealing. These may occur only under certain conditions - like when you are stopped and ease up off the brakes just enough to inch forward, lightly brake in a turn, etc.
I like to do a lot of the more simpler maintenance jobs on my vehicles. Replacing brake pads falls into this category, so I've done exactly what you are thinking of on a number of ocasions. My 'road test' consisted of finding a 'safe' place - getting up to a decent speed, and slamming on the brakes as hard as I could. I'm not going to recommend this of course... It did tell me what my maximum braking power was, though.
At any rate, I found that it was pretty close costwise between having the rotor turned, and just plain buying a new rotor from an autoparts store and installing it myself.