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  1. #1
    darkstar's Avatar
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    Default Cross-drilled rotor warping

    Has anyone experienced rotor warping on their Z-51 (J-55) heavy duty brakes. I have only 9300 miles on my 08 and had bad warpage. The dealer machined the front rotors for me and this seemed to fix the problem. I just thought it was a bit soon.

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    High heat causes most of the out of round conditions or warped rotors....panic stops and aggressive driving with frequent higher speed stops will also contribute to that condition....,

  3. #3
    darkstar's Avatar
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    Quote Originally Posted by wallyknoch View Post
    High heat causes most of the out of round conditions or warped rotors....panic stops and aggressive driving with frequent higher speed stops will also contribute to that condition....,
    Thanks. I have owned 4 vettes in my 60 years and have never had this condition. I thought I paid for a better brake that can handle the more aggressive braking. (within reason)

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    I've had the standard rotors warp on the C6 but not the cross-drilled rotors - yet.
    In my case, it only took 11 laps on the Texas Motor Speedway in-field road course.

    I've found that improperly torqued lug nuts can warp the rotors also.
    Tuna
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    "Rotor warping" is widely misunderstood and that misunderstanding is leveraged by service vendors to make money selling customers rotor machining.

    First, never machine rotors unless, after performing visual inspection and measurement procedures mandated by the service manual in brake diagnosis, you determine it's required.

    Brake service techs love to machine rotors, even when it's not required because 1) you pay them to do it and 2) it shortens the life of the rotor thus bringing the time a new rotor must be purchased closer. Making this worse is brake service tool manufacturers and replacement parts mfg's. train techs to cut rotors no matter what because this sells more brake lathes and brake rotors.

    In the case of brakes which are driven normally (ie: not abusive driving or race track use), C6 rotors seldom warp in the literal sense. This is not to say that rotors never warp, but it is to say that they actually warp far less often than many laypersons believe.

    What can happen is transfer of pad material to the rotor brake plates or friction surfaces caused by lack of occasional aggressive use of the brakes. Once this happens, you'll feel a mild shudder on light to medium brake applications with no pedal pulsation but less shudder on a heavy application. The shudder is caused by varying coefficients of friction on the brake plates which in turn cause a rapid fluctuation of deceleration which most of us interpret as warped rotors. Keep in mind that this vibration's vector is longitudinal rather than lateral as you'd get if the rotors were truly warped. A very sensitive person using the brakes very judiciously can actually tell the difference. If you brake with very consistent light-to-medium pressure, just before the car comes to a stop, the frequency of the fluctuation in decel. will become low enough that you can feel a sort of jerking back and forth. If you feel that, the problem is more likely transfer of pad material than it is rotors that are physically warped.

    The proper solution to this is more time consuming than just throwing them on a brake lathe and involves abrading the brake plates to remove the pad material which takes more time but removes far less material.

    Finally, remember that only way to determine if the rotors are warped is to measure them. Most service vendors don't bother and, when a customer comes in complaining of warped rotors or brake shudder, they just machine the rotors which is often a temporary fix if there's a problem with pad material transfer.

  6. #6
    darkstar's Avatar
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    Quote Originally Posted by Hib Halverson View Post
    "Rotor warping" is widely misunderstood and that misunderstanding is leveraged by service vendors to make money selling customers rotor machining.

    First, never machine rotors unless, after performing visual inspection and measurement procedures mandated by the service manual in brake diagnosis, you determine it's required.

    Brake service techs love to machine rotors, even when it's not required because 1) you pay them to do it and 2) it shortens the life of the rotor thus bringing the time a new rotor must be purchased closer. Making this worse is brake service tool manufacturers and replacement parts mfg's. train techs to cut rotors no matter what because this sells more brake lathes and brake rotors.

    In the case of brakes which are driven normally (ie: not abusive driving or race track use), C6 rotors seldom warp in the literal sense. This is not to say that rotors never warp, but it is to say that they actually warp far less often than many laypersons believe.

    What can happen is transfer of pad material to the rotor brake plates or friction surfaces caused by lack of occasional aggressive use of the brakes. Once this happens, you'll feel a mild shudder on light to medium brake applications with no pedal pulsation but less shudder on a heavy application. The shudder is caused by varying coefficients of friction on the brake plates which in turn cause a rapid fluctuation of deceleration which most of us interpret as warped rotors. Keep in mind that this vibration's vector is longitudinal rather than lateral as you'd get if the rotors were truly warped. A very sensitive person using the brakes very judiciously can actually tell the difference. If you brake with very consistent light-to-medium pressure, just before the car comes to a stop, the frequency of the fluctuation in decel. will become low enough that you can feel a sort of jerking back and forth. If you feel that, the problem is more likely transfer of pad material than it is rotors that are physically warped.

    The proper solution to this is more time consuming than just throwing them on a brake lathe and involves abrading the brake plates to remove the pad material which takes more time but removes far less material.

    Finally, remember that only way to determine if the rotors are warped is to measure them. Most service vendors don't bother and, when a customer comes in complaining of warped rotors or brake shudder, they just machine the rotors which is often a temporary fix if there's a problem with pad material transfer.
    You have said a mouth full for this layman. I let the dealer make the decision using measured runout as a basis. He did machine the rotors under warranty.
    However he did not replace the pads and I notice a not full contact with the rotor. I observed this by looking at the scratch contact on the rotor. I just figured the pad will wear eventually. The problem seems to be fixed for the time being.
    I thought that the J-55 brakes were of a very high quality and not so suscepticle to warpage with so few miles. I drive I-5 interstate here in washington where good brakes are a must have. I don't ride them.
    Perhaps Tuna has it. I trust the dealer to torque the lug nuts to specs.
    I thank you for your time
    Ray

  7. #7
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    Hib's right on this. Uneven pad material transfer can cause "stick/slip" friction differences on the brake's swept area. This causes a "grabbiness" sensation with the car (more noticed @ extremely slow speeds). "Warped" rotors are a great revenue generator.

    Think about this:
    If a rotor has excessive runout on one side of the rotor, then the underside of the rotor will have the exact same runout-only in the opposite direction, thus cancelling out any pedal pulsation. The brake pads that are pushed into the caliper by the runout are cancelled out by the pads on the otherside of the rotor coming out to take up the runout on the otherside of the rotor. The pads will move back and forth inside the calipers-in unison. There would be no pulsation @ the pedal. Only a fluid transfer in the fluid ways of the caliper. I doubt a driver could feel this as the pedal is so far away and the diameter of the lines is so small.
    Drag racers purposely shim their rotors and cut them to "wobble" to reduce brake pad drag on the rotors. When they hit the brake, the pads simply oscillate in the calipers with a steady pedal.

    I think "warpage" is from the old days of drum brakes.

    It's a consumer ripoff, kinda like the "3000 mile" oil change rule...

  8. #8
    darkstar's Avatar
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    Quote Originally Posted by NORTY View Post
    Hib's right on this. Uneven pad material transfer can cause "stick/slip" friction differences on the brake's swept area. This causes a "grabbiness" sensation with the car (more noticed @ extremely slow speeds). "Warped" rotors are a great revenue generator.

    Think about this:
    If a rotor has excessive runout on one side of the rotor, then the underside of the rotor will have the exact same runout-only in the opposite direction, thus cancelling out any pedal pulsation. The brake pads that are pushed into the caliper by the runout are cancelled out by the pads on the otherside of the rotor coming out to take up the runout on the otherside of the rotor. The pads will move back and forth inside the calipers-in unison. There would be no pulsation @ the pedal. Only a fluid transfer in the fluid ways of the caliper. I doubt a driver could feel this as the pedal is so far away and the diameter of the lines is so small.
    Drag racers purposely shim their rotors and cut them to "wobble" to reduce brake pad drag on the rotors. When they hit the brake, the pads simply oscillate in the calipers with a steady pedal.

    I think "warpage" is from the old days of drum brakes.

    It's a consumer ripoff, kinda like the "3000 mile" oil change rule...
    I agree with all and appreciate the info. I may have mistaken the termanology. Rotors are measured by lateral runout for eveness as I know it. I used the term warpage because when I applied those massive brakes the whole vehicle shuttered strongly especially going downhill at only 40-50 mph.
    I don't recall feeling the pedal pulsate. I was always looking for cops on this particular hill.
    Don't want to beat this to death. I was just very surprized that my high dollar brakes with those massive cross-drilled rotors would do this so soon.
    Again thanks
    Ray

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    Quote Originally Posted by darkstar View Post
    I agree with all and appreciate the info. I may have mistaken the termanology. Rotors are measured by lateral runout for eveness as I know it. I used the term warpage because when I applied those massive brakes the whole vehicle shuttered strongly especially going downhill at only 40-50 mph.
    I don't recall feeling the pedal pulsate. I was always looking for cops on this particular hill.
    Don't want to beat this to death. I was just very surprized that my high dollar brakes with those massive cross-drilled rotors would do this so soon.
    Again thanks
    Ray
    It is very common to equate brake shudder with warpage.

    "Warp," when used in the context of brake rotors, generally means the brake plates physically change shape due to heat cycling or abuse during service work (such as overtightening wheel nuts or not tightening them in a stepped, star pattern) This change in shape can be thickness variation, nonparallelism or "waviness".

    While machining can sometimes eliminate any of those qualities up to the extent of the rotors' minimum thicknesses, sometimes, brake shudder, especially that which you feel at light brake applications and not accompanied by pedal pulsation or steering wheel shake, might not be caused by changes of the rotors' dimensions or geometry.

    Now if you get shudder, pedal pulsation and/or steeering wheel shake then the rotors, at least the fronts, maybe actually be warped.

    Suffice to say that there is much misunderstanding of the causes of brake shudder, even in the professional service technician community.

    With this particular car...what I'd do is: take it out in the boonies where you can make some 70-80 mph stops on a straight road. Run the car up to about 80, then, get hard on the brakes to just before ABS. Do this 3 or 4 times with five miles or so driving at highway speeds in between each to cool the brakes. Often that "wipes" pad transfer off the rotors.

    If you do this and the shudder is less or eliminated, it's unlikely you have warpped rotors.

  10. #10
    darkstar's Avatar
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    Quote Originally Posted by Hib Halverson View Post
    It is very common to equate brake shudder with warpage.

    "Warp," when used in the context of brake rotors, generally means the brake plates physically change shape due to heat cycling or abuse during service work (such as overtightening wheel nuts or not tightening them in a stepped, star pattern) This change in shape can be thickness variation, nonparallelism or "waviness".

    While machining can sometimes eliminate any of those qualities up to the extent of the rotors' minimum thicknesses, sometimes, brake shudder, especially that which you feel at light brake applications and not accompanied by pedal pulsation or steering wheel shake, might not be caused by changes of the rotors' dimensions or geometry.

    Now if you get shudder, pedal pulsation and/or steeering wheel shake then the rotors, at least the fronts, maybe actually be warped.

    Suffice to say that there is much misunderstanding of the causes of brake shudder, even in the professional service technician community.

    With this particular car...what I'd do is: take it out in the boonies where you can make some 70-80 mph stops on a straight road. Run the car up to about 80, then, get hard on the brakes to just before ABS. Do this 3 or 4 times with five miles or so driving at highway speeds in between each to cool the brakes. Often that "wipes" pad transfer off the rotors.

    If you do this and the shudder is less or eliminated, it's unlikely you have warpped rotors.
    Cannot do that now as the dealership machined the rotors after diagnosing the fronts as "badly warped". I lost some rotor but the problem seems to be eliminated. Can you shed some light on your opinion of the J-55 heavy duty brakes (cross-drilled).

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    My opinion of cross drilled rotors is they are a waste of money and are cosmetic only.

    That said, I think where you were going with the question was do drilled rotors tend to be more likely to warp. I have no test data to support this but my gut feeling is not in cases were the duty cycle is normal driving or aggressive street driving.

    Now that the rotors have been cut, it's impossible to determine what the problem really was.

  12. #12
    darkstar's Avatar
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    Quote Originally Posted by Hib Halverson View Post
    My opinion of cross drilled rotors is they are a waste of money and are cosmetic only.

    That said, I think where you were going with the question was do drilled rotors tend to be more likely to warp. I have no test data to support this but my gut feeling is not in cases were the duty cycle is normal driving or aggressive street driving.

    Now that the rotors have been cut, it's impossible to determine what the problem really was.
    I was under the impression they were cross drilled so as to help in the elimination of heat, thus less chance of warpage or whatever. Whenever i do replace them, I will get a solid or slotted disc.....thanks

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    "Front end "shudder" can be caused by:
    1. Out of balance tire
    2. Out of round tires
    3. Wheel bearings loose or improper torque
    4. Worn or loose ball joints
    5. Partially sheared Pitman arm
    6. Loose rack
    7. Cracked frame
    8. Brake issues (as stated earlier.)
    9. Damaged wheel

    This isn't a complete list, just off the top of my head.

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    A long time ago, rotors on road racing cars were drilled to allow venting of gasses emitted by the brake pads. The theory was that in cases were the pads got really hot, this "pad outgassing" would cause a thin "boundary layer" of gas to get trapped between the pad and the rotor, decreasing the friction that provides braking.

    Road racers began to drill holes in the rotors to vent this gas into the rotor cooling air flow.

    After a few years, street drivers looking for an ego pump and figuring making their brake look racy, drilling holes in the rotors would do it, jumped on the drilled rotor bandwagon. The rest is history with the aftermarket and now even OEs making drilled rotors.

    In the meantime, drilled rotors never had any functional purpose on a street car

    Today, they are no longer necessary in racing, either, because of improved technology in brake pads.

    Retired Chief Engineer David Hill acknowledged to media during the media preview for the 2005 Corvette in the summer of 2004 that the holes in the rotors were strictly cosmetic.

  15. #15
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    Quote Originally Posted by Hib Halverson View Post
    A long time ago, rotors on road racing cars were drilled to allow venting of gasses emitted by the brake pads. The theory was that in cases were the pads got really hot, this "pad outgassing" would cause a thin "boundary layer" of gas to get trapped between the pad and the rotor, decreasing the friction that provides braking.

    Road racers began to drill holes in the rotors to vent this gas into the rotor cooling air flow.

    After a few years, street drivers looking for an ego pump and figuring making their brake look racy, drilling holes in the rotors would do it, jumped on the drilled rotor bandwagon. The rest is history with the aftermarket and now even OEs making drilled rotors.

    In the meantime, drilled rotors never had any functional purpose on a street car

    Today, they are no longer necessary in racing, either, because of improved technology in brake pads.

    Retired Chief Engineer David Hill acknowledged to media during the media preview for the 2005 Corvette in the summer of 2004 that the holes in the rotors were strictly cosmetic.
    I notice on the 1990 ZR-1 that the rotor is cross drilled and slotted. Also I notice that alot of aftermarket brake kits feature slotted rotors only. Is this the best way of cooling currently ?

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