Z-man

Yep - dial indicators do not lie. Rotors can be non-flat. Is it the metal actually warping? Pad depost? Manufacturing defect? Doesn't matter - the result is the same - they need to be cut/shaved or replaced.

On cutting or shaving the rotor - for street application, this can be a short term solution. The problem is, you now have a rotor that has uneven thickness. Guess what? The warping will occur again, and sooner this time. For track application, I don't recommend cutting the rotors at all. Replacing rotors with new ones is cheaper than body damage cause by a failed rotor going into turn one...

-Z-man.

Matt H

Z-man, you can cut a rotor using both sides of the lathe (and almost always do). Generally, we start with a .0020 cut. Regardless of what they claim I can show you in about 30 seconds what a warped rotor looks like (or one with pad deposits, etc). Take a rotor, set the lathe to .0010 and see where it cuts and where it doesnt.

My general rule of thumb was if the rotor didnt have at least .0030 over the nominal thickness it didnt get turned. Composite rotors never get turned and BMW/Mercedes rotors never get turned (they are low dollar items anyhow).
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testarossa_td

Interesting article right or wrong....I have seen warped rotors....of course it was on a car that had an engine fire and not a small one
Now I don't recall that article mentioning vented vs solid rotors.

cjeckert

His argument has very vallid claims and in most instances he is correct that you wont warp routers in nermal driving conditions mainly for the fact that iron dosnt crack or warp when up shocked, however a downshock is quite a different story and it is quite bealivable that you can pysically warp a router if it is drenched in water after being very hot. Mike E. Eberhart gives a good explanation of this in his book Why Things Break

Matt H

cj - that might be 100% true if all rotors were made of cast iron...but they arent.
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Robert D

Keep in mind this is an american car guy; he is probably correct for most of the cars out there on the roads which are not high performance cars (ie Ford Caravan, Chevy Cavalier, Trucks, etc.)

However, I have seen warped rotors on a Mitsubishi 300GT VR-4; where the rotors did warp as the brakes were not large enough for the car and in DE's the brakes would get very high and the brakes would fade. I'm not too sure about it being the pads which cause the need for rotors to be turned...my thoughts are OEM rotors have lasted longer than aftermarket rotors I've used, before needing to be turned/resurfaced.

Matt H

Robert - most american cars now use composite rotors, Chevrolet and Chrysler went to them ages ago. I have almost never seen a warped rotor on a truck, though the rears rotors on trucks that tow seem to be pretty bad.

Most aftermarket rotors are made by OEM suppliers (though certainly there are varying levels of quality). I have actually bought rotors for older Hondas that cost 8 bucks.
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emwporsche

ever tried UNwarping your rotors?

in mild cases I would always get the brakes as hot as possible,
then drive around with the brakes on, essentially straitening them out.

Robert D

I'm saying most domestic cars DO NOT have warped rotors.

The OEM rotors I am talking about are for the 944...the aftermarket rotors, which I paid a shop OEM prices for, warped within 10k miles. I've heard this is normal with cheap aftermarket rotors and that a resurface corrects them for a long while. The true OEM rotors lasted much longer IMO (up until the death of my car).

I just think the vast majority of automobiles are not true high performance cars and do not heat up (or are not driven hard enough) the brakes enough to cause true rotor warping.

Matt H

I agree they are not performance cars. However, I will let you in on a secret; soccer moms and grannies warp rotors worse than sports car guys ever will.

Rotors that are stored on the end of the box rather than flat tend to have more problems as well...
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Robert D

Is that why brake check stores theirs on the end of the box?

Matt H

It is more a function of space and if they are used quickly it poses no issue. It is the ones for a 77 Vega that sit forever that become the problem!
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formerGMguy

Pre-93' GM W-body cars are notorious for warping rotors. The brakes are way undersize, I believe the fronts are 10.25" vented are the rears are 10" solid disk. Pretty tiny when you consider that your stopping a 3400lbs object. I went through 2 sets of OEM quality pads and rotors in something like 20k miles on my Cutlass before upgrading to the 96'+ fronts (11.25" rotors) and 94' and up rears (new caliper design). To this day the brakes still have horrible feel, and fade badly. Worst brake design in the history of the automobile.

There's no way anyone is going to convice me that rotors don't warp.

Z-man

Matt - I was trying to say "I believe rotors warp" without using the term warp (ie: non-flat.)

I am in the camp that believes rotors can appear to be warped for anumber of reasons: metal 'bending,' deposit of brake pads, and manufacturer's defect are the top three I can think of.

-Z-man.

Matt H

I never did do runout checks on new rotors, that might be interesting, to see how many were cast "warped" I bet the number is quite high.
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