Rotors don't warp?

Based on a couple of references I have seen on other thrreads, did I miss the discussion that rotors don't really warp?

How about drums?

Rotors can definitely get warped. That's due to repeated heating/cooling which shrinks the metal in places. It's easily seen when they are resurfaced with a brake lathe, you'll see the high spots first.

The 'hat' on composite rotors can get warped either by overtorquing the lugs or again by heat.

These are fairly unusual occurrences, though. The #1 cause of brake vibration is material from the pad getting 'stuck' on the rotor, this causes varying friction points as well as a small difference in thickness and that's what leads to vibration. That's why most mfgs now recommend that instead of turning them on a brake lathe that they be resurfaced using a 'whizz wheel' on a die grinder to give a non directional finish.

Drums too can warp and it's not hard to do. I saw a demonstration years ago where a drum was measured with a drum micrometer in four different spots. The guy then picked up the drum, squeezed it hard between his hands and rechecked it; it was now .060 out of 'round'. Before everyone says 'had to be some sorry dinky little furrin' car drum', it was a garden variety 11 inch GM brake drum. By the way, that is why drums come in a box marked 'do not store on edge'.

When you hit the brakes and the shoes contact the drum, the drum will actually go elliptical. It 'snaps back' most of the way when the pressure is taken off. In the end analysis, drum warpage is a lot like rotor warpage; it's localized hot spots that shrink the metal.

I saw reference to that in the myth thread too. I say they most definitely warp, and it's pretty damn common. We've got a brake lathe here at work, and we put fresh brakes on all the cars on our used car lot. I'd say about half of the rotors we turn are at least slightly warped. If they don't warp I'd like to know why the lathe only sweeps 2/3s of the rotor half of the time.

Rotors warp. The frount set on my 924s are pulsing at the moment. Indicating the need some attention.

Rotors warp. Especially if the car of origin starts with an F, and is from the 90's....

grumble, grumble, grumble......

16vCorey wrote: I saw reference to that in the myth thread too. I say they most definitely warp, and it's pretty damn common. We've got a brake lathe here at work, and we put fresh brakes on all the cars on our used car lot. I'd say about half of the rotors we turn are at least slightly warped. If they don't warp I'd like to know why the lathe only sweeps 2/3s of the rotor half of the time.

Is it possible that you aren't actually mounting them square on the lathe? A little rust on the mounting surface can create the same effect.

alfadriver wrote: Rotors warp. Especially if the car of origin starts with an F, and is from the 90's.... grumble, grumble, grumble......

The composite rotors on the early Taurus were flippin' atrocious. The 'hat' would warp if you shone a drop light on it.

alfadriver wrote: Rotors warp. Especially if the car of origin starts with an F, and is from the 90's.... grumble, grumble, grumble......

Stupid Ferraris....

Curmudgeon wrote: By the way, that is why drums come in a box marked 'do not store on edge'.

And that is why I don't buy Retread Auto rotors or drums anymore. Their plan-o-gram of garbage made them place nearly every rotor and drum on edge, even with the box saying not to do so.

And here I just thought they blew apex seals

alfadriver wrote: Rotors warp. Especially if the car of origin starts with an F, and is from the 90's.... grumble, grumble, grumble......

Ferrari (sp) ?

Rotors do warp. Not nearly as often as they get uneven pad transfer, or have a chunk of rust land between the hub and rotor. Its kind of a moot point, though, because the solution to all is to clean all the rust from the mounting surfaces, then machine or replace the rotors.

My opinion- if it shakes at highway speed worse than low speed, its warped. If you notice it more just as you are coming to a stop, its pad transfer.

Someday I'd like to test this theorey by just sandblasting the friction surfaces and reinstalling the rotor. Shake gone? Must have been pad transfer.

I don't think the vented rotors used on cars warp anywhere near as much as people tend to claim. Not saying they absolutely never do, just that I've never seen indication of it being much.

Only rotors I could positively identify as truly warping were the solid rotors. Easily straightened with a hammer btw. And it still wasn't much.

As for the lathe, take a rotor off and put it right back on. Admire how it's now cutting a different area. Brake lathes are not exactly precise. And yes, the the rust and dirt makes a heck of a difference.

Rotors definitely warp - there's no reason they shouldn't, given the aspect ratio of the shape and their duty cycle.

I think where the 'myth' aspect comes in is that EVERY pulsing brake pedal is blamed on warped rotors, when probably half of the incidents or more actually are deposited brake material.

My main complaint about my wife's TSX is a lightly pulsing brake pedal. It developed that with under 10,000 miles from new, under a very light usage cycle (the car only gets about 4500 easy miles a year). Finally, by 25,000 I couldn't stand it any more and replaced the front brakes with new Brembo rotors and Akebono pads, with new fluid.

Now, in a bit under 10,000 miles, it's starting to do it again even though I didn't use OEM parts. I think the calipers just leave the pads too close to the rotor surface and crap sticks to them.

Had a 97 Grand Am GT. Rotors lasted about 3 months. 6months tops.

at the same time owned a 95 Olds Achieva Base model (same car essentially, non-gt "glass"). Replace the rotors once in 5 years.