Brake rotors newbie help!!

[driven2drive]

Hey guys,

I'm really not too car savvy, so please bear with me. What are the minimum thickness specs for the front and back rotors? I think the stock rotors (which I have now) come originally 1.26in/1.02in for front and back respectively.

Another question is, do rotors wear down for any other reason other than having them turned or having messed up pads? Does driving under normal conditions wear down the rotors? It shouldn't right? I mean, that's why the pads are there with the special material that wears down, not the rotor.. Or am I wrong?

I haven't had any problems with them yet. I've had my pads changed a few times in the past but the mechanic at Midas told me I needed to turn the rotors (I probably didn't need them turned). This was 2 years ago. Under normal circumstances, should there be any reason why I need new rotors now if they're not warped? I'm sure I need new pads though...

Thanks in advance,

Mike

[SupremeCutlass]

rotors will wear down too, it just takes a while.

[curtis73]

Post what car and year it is. All brake rotors have different minimum thicknesses.

Also, rotors don't warp. They get deposits and silica crystalization, but they don't warp. Read about it here: http://www.stoptech.com/tech_info/wp...rakedisk.shtml Don't worry, nobody seems to know about it yet, including almost every service tech that exists on the planet

As long as turning down your rotors doesn't take them down less than the minimum thickness, you're fine to machine them. Just make sure you properly bed in the new pads or they'll pulse and you'll just have to do it all over again.

[TheSilentChamber]

The minimum thickness will also be stamped or cast into the rotor.

[Moppie]

Originally Posted by curtis73

Also, rotors don't warp. They get deposits and silica crystalization, but they don't warp. Read about it here: http://www.stoptech.com/tech_info/wp...rakedisk.shtml Don't worry, nobody seems to know about it yet, including almost every service tech that exists on the planet

Iv seen this before, and thought it a bit odd.
Iv seen several "warped" discs being machined "flat" again, and in extreme cases you can actualy see the wobble in the disc, and the material being removed is certianly not deposits of pad and disc material, just cast iron disc.

[curtis73]

Well, they certainly do get runout, but its just from cementite inclusions and pad deposition. Not entirely sure I'm competely with it either, but it appears to be the case on the ones we cut in radial cross-section to check.

[zagrot]

Originally Posted by curtis73

Well, they certainly do get runout, but its just from cementite inclusions and pad deposition. Not entirely sure I'm competely with it either, but it appears to be the case on the ones we cut in radial cross-section to check.

where do you work that you would perform such a test? i'm fairly sure that the average person would not be able to conclude anything from the cross section of a brake disk. if you have good picture of the cross section of a disk that shows anything meaningfull, could you post them?

[curtis73]

We just cut it in several sections with a band saw and looked at it under an electron microscope. Since I'm no longer a college student in microbiology, I don't have access to an electron microscope anymore but if I'm around one I'll let you know

The chemistry behind it is sound, but like Moppie said, its hard letting go of the infallible logic behind rotors warping. And like I said, I'm not fully convinced they don't, but in light of my most current information, the cementite inclusions make more logical sense to me. But, there is no conclusive evidence that I can provide either way.

[TheSilentChamber]

He also speaks of that from a racing standpoint, Most racing rotors are designed a little differnt as most are two piece. This eliminates most of the distortion you will see on a street use designed car, mushrooming of the rotor at high temps. While he may be right- sounds like he knows more than I do- I still have a hard time automatically using that theory for every case.

[zagrot]

ah, university resources; that is one reason that i am anxious to get back into school. since chemistry is one of my interests i was surprised to to hear someone remark on observing the presence of cementite inclusions in cast iron since they are not visible to the naked eye, nor could you see a layer of deposited brake material. i guess it was worth a try.

[AlmostStock]

From the posted article: With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification

I always thought rotor warping was due to over torquing the lug nuts, especially on lightweight rotors. Even this guy seems to allow for the possibility of this. Unfortunately, most shops just wham away with the impact wrench when they service cars.