CAVU

Safety first, where a suitable dust mask and leave the shop clothes in the garage. Pads are not asbestos but I still respect that the stuff is probably not the healthiest stuff to ingest.

No need to remove material from the rotor since you have found the problem. Just go after it with some more sanding cycles and it should go away.

You should also take the brake pads and sand each braking surface slowly against sandpaper sitting on a flat surface to reveal virgin breaking surface. It will only take a couple of cycles.

Then it is off to the road for some proper bedding.

TomF

+1

Cheers,
TomF

TomF

^This^

Cheers,
TomF

RAudi Driver

Yes hot spots on rotors can make the brake pedal pulsate.

mtnrat

Update. I drove around for a bit and decided the 90% improvement was placebo. So I took the rotor off again and gave it a better sand and also sanded the pads. No difference. I took it off again and went to my buddies shop. He found a little runout and removed 5 thou from each side. The brakes are now working as they should.

ScootCherHienie

Out of curiosity... were the rotors surfaced while mounted on your Cayenne or were they removed for surfacing off the car? Stubborn cases can sometimes be resolved by resurfacing the rotors while they are mounted on the vehicle... though you need the special equipment to do this.

extanker

checked and fixed on a lathe.....why am i not surprised ? oh i know because i am not a 5 minute google expert mechanic but really REPAIRED things . to the op...good it is fixed sorry you had to go through all the hbo drama from the experts

mtnrat

Removed and put on a brake rotor lathe.

mtnrat

lol, No problem. I don't mind trying the the least invasive ideas first and going from there. I am pretty much retired so I have the time and have a good friend, (the indy that turned my rotor), who has helped me along on many auto projects, usually shaking his head. I did learn a lot about brakes though.

deilenberger

Most high volume brake shops have the on-car lathe.. places like Firestone, Meineke. When they replace pads (only) they commonly use one to skim cut the rotors and expose a fresh flat surface. As long as cutting doesn't result in the rotor going below spec - it should work fine.

And as far as "warping" - care to re-read what I posted above about over-torqueing causing warping. Anyone who dogmatically says "brake rotors don't warp" hasn't really been working on vehicles all that long. I've certainly seen warped ones - probably from poor mounting (dirt under the seating surface on the hub) or over-torqueing of the wheel bolts. Give a shop monkey an impact gun and ask him to rotate your tires and watch how he does it..

Bzzzztttt, off. Bzzzzttt, bzzzzzt, bzzzzzy - back on. Stop when the impact gun stalls. A torque wrench is never seen, and it's rare that a torque-stick is seen in use (I insist on seeing the torque stick before I let them touch my wheels..)

RAudi Driver

I've always been led to believe that a rotor can warp. Not in the sense that the metal is actually bending, but wearing unevenly. This is caused by overheating the rotor where the pad actually starts wearing out the softer areas (less dense spots) of the rotor, thereby causing an uneven surface, hence the term warp as the surface is no longer straight and flat.

Matt O.

This is incorrect. See discussions above.

Additionally, most people who use that term "warped rotors" are actually implying the rotor bends under the stress of the heat. Given the fact the manufacturing process requires heat 3-4 times that of braking even in extreme conditions, that also makes no sense. There are two very simple explanations for "warped rotors" and they have been discussed above.

Also, I find it hard to believe that I can warp a piece of metal the size of a rotor by over-torquing or using an impact wrench to install lugs. The threads on the lugs would break far sooner than a inch of heat treated steel would bend.

Mechanical engineers, please correct me if I am
wrong.

AGARubberDuck

An argument isn't what I'm after and the 'warpable' vs 'not-warpable" crowds may just have to agree to disagree, but to further the discussion, why do you suppose there is a minimum spec? If a buildup is the only reason a rotor will have pulsating stopping power, you should be able to turn town the high spots indefinitely.
Whether the brake problem is due to uneven heating and cooling (changing the shape of the rotor dimensions), or some combination uneven adhesion/friction creating high and low spots with the end result of the rotor surface not being true, doesn't that basically define 'warped'?

deilenberger

You're wrong. the metal on the hub of a rotor is closer to 3/16" of an inch thick.

If that metal is distorted due to improper use of an impact-gun or over-torqueing (and not tightening in a gradual crisscross pattern) or inadequately cleaning the hub surface when replacing rotors, then the rotor won't seat properly on the hub, causing runout that can be described as warping. BTDT.

The "inch of heat treated steel" doesn't have to bend to become useless - once the hub is distorted the "inch" of steel no longer travels true to the hub, and the rotor is then worthless.

There is a reason for using a crisscross tightening pattern, just like there is a reason for torqueing other components (like a cylinder head) in the same manner.

It happens. Particularly at fast-tire change places. A good shop will show you their torque wrench, or torque-sticks (basically extensions for an impact wrench that limit the torque transferred to the socket.) And there is a reason that torque-sticks exist.

J'sWorld

Lifetime buddy, lifetime. HBO is sooo yesterday.

On a side-note I found that cryo treated rotors perform much better in regards to the ill effects of heat cycling. Well worth it. I also found that it is alsmost impossible to have to have your cake and eat it too when it comes to noise/dust/performance in regards to brakes. I have also found that the less agressive the pad and more low dust it is (which go hand in hand) the more heat problems you will have with rotors.