Quote:
Originally Posted by iceNine
I would think that warping (the plate becoming deformed so that it is no longer "flat") could be confirmed by testing runout using a fixed feeler gauge. I don't have it in front of me but I remember that the BGB has a description of this test and acceptable tolerance numbers for runout on the rotors.
Sorry for asking a stupid question, but if the rotor is really not flat anymore, why would resurfacing fix it? I assume that to get it flat the cutter would take off more material from one portion of each surface than other portions and the result would be a plate that does not have the same weight/balance all the way around. Just curious since I usually get slotted rotors so when they go bad I have to replace them.
And the pad material buildup that I have been aware of on my brakes has been very obvious since I will have visible pad outlines on the rotor. I have even tried fine sandpaper to see if I can get any off and they don't come off.
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Regarding the 'why resurface a rotor that is actually warped': that's a very good question, and one that no one really addresses straight out. It is definitely common place to call the rotors warped, when they reach the point that they create the braking and sometimes, slight steering vibrations that we are all familiar with. How can resurfacing them be a good idea. Well, apparently the warpage is of such a small amount that a minor trim of the rotors works quite well, at least for a short period of time. I would guess, that as to the weight and balnace issue, of the rotors, after such a process that because the rotor mass is so much smaller than that of the wheel and tire, it does not present the same issue as an unbalbalnced wheel assembly. I've thought about that one before, and that's about the best I can come up with.
Yes, the BGB goes over how to check for rotor runount, but the equipment used is not something the avergae do-it-yourselfer has lying around. I believe they call for a specific runout guage to be used.
I have also seen the occasional pad outline on my rotors, more particularly on the rear, after it has been parked for some time after having been driven through the wet, but it has always disappeared after a relatively short drive. Its usually a bit of a rust like material, probably from the partial metalic compound in the R4S pads I use. I really love it when it has sat for a very long time after being wet and the rear pads don't actually release when you let off the emergency brake, but as you start to drive away. The first time or two I heard that I thought part of my rear brake system was coming apart.
The only other material I might notice is possibly pad material that gets ground into the rotor as it develops scoring from normal use, but I would consider that quite normal.