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Thread: Warped discs and other myths

  1. #1
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    Warped discs and other myths

    http://www.stoptech.com/tech_info/wp...akedisk.shtml#

    This guy has been involved in racing for a while (including Ford's GT40 campaign!), so he has some first-hand knowledge.

    Chip H.

    Former owner: 2012 Honda Civic LX, 2006 Honda Ridgeline RTL, 2000 Honda CR-V EX, 2003 MINI Cooper S, 1992 Honda Accord LX, 1999 Mercedes ML-320, 1995 VW Jetta GLX, 1991 Mercury Capri XR2, 1981 Mercury Zephyr, 1975 Chevrolet Impala

  2. #2
    mrblanche
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    Re: Warped discs and other myths

    I just posted a message on another forum to a guy who is a brake expert. I'll see what he says. He knows more about automotive brakes than the man who invented automotive brakes (since that guy is dead, right?).

  3. #3
    mrblanche
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    Re: Warped discs and other myths

    OK, here's his response:

    >>I don't totally disagree with him because I have seen what he is talking about happen especially with semi metallic friction material...but for him to say that he has "never" seen a warped rotor either on a race car or a street car is an asinine thing to say. If you number a 4 or 5 lug hub and tighten number 1 lug to 80 foot pounds and number 3 to 100 foot pounds and number 4 to 75 foot pounds and take the car out and heat up the rotor to 300-400 degrees...the rotor will conform to the way the wheel lug has been tightened. Then you take the car home and park it in the driveway and the rotor cools off...believe me...IT IS WARPED<<

  4. #4
    Vulture of The Western World Eric's Avatar
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    Re: Warped discs and other myths

    Quote Originally Posted by mrblanche
    OK, here's his response:

    >>I don't totally disagree with him because I have seen what he is talking about happen especially with semi metallic friction material...but for him to say that he has "never" seen a warped rotor either on a race car or a street car is an asinine thing to say. If you number a 4 or 5 lug hub and tighten number 1 lug to 80 foot pounds and number 3 to 100 foot pounds and number 4 to 75 foot pounds and take the car out and heat up the rotor to 300-400 degrees...the rotor will conform to the way the wheel lug has been tightened. Then you take the car home and park it in the driveway and the rotor cools off...believe me...IT IS WARPED<<
    This is why many OEMS insist that wheels be installed using a torque wrench and by hand, to the correct value - not with an air gun, which may lead to over-torquing the lugs, thus resulting in warped rotors.

  5. #5
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    Re: Warped discs and other myths

    Some good stuff there, but some not so good.

    Firstly, warped discs.....I've had them.

    His procedure for 'breaking-in' pads may be relevant to racing pads, but for pads for road use it just isn't necessary & could even be dangerous. If the pads need to see high temperatures to achieve their optimum friction levels there's a danger that they will fade the first few times they are taken up to temperature; not desirable on a public road! For this reason friction material manufacturers will incorporate a scorching operation in the production process. After final grind & before painting the pad material is heated to a temperature higher than it is likely to see in service, thus assuring that when fitted to the vehicle it performs as intended right from the start.

    He's missed an important reason why cast iron is preferred over steel for discs - higher friction. For a given pad material the coefficient of friction on cast iron will be 15-20% higher than on steel. A lot of motorcycles do use stainless steel discs, but for cosmetic reasons rather than performance. To compensate for this, bike pads typically have higher friction levels than their car counterparts - sintered pads are common on bikes whereas cars are mainly organics.

    As for his comments on brake fluid reservoirs.......

    The fluid level warning light is NOT there to warn that the pads need replacing. It's there to give a warning that......yes, you guessed it, the brake fluid level is low! On most cars the pads will be worn out before the fluid level warning light comes on, which is why most cars nowadays have some form of pad wear indication, usually, at least on European cars, operated by a wire embedded in the friction material. When the pad wears down to expose the wire the wire contacts the disc& completes the circuit which operates the warning light. Some American cars have a simpler system - a spring attached to the pad backplate contacts the disc surface & makes a loud screeching noise to alert the driver to worn pads.

  6. #6
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    Re: Warped discs and other myths

    I have had warped rotors on three cars, all of them Fords. Ford uses cheap materials and it shows in their brake systems. I'm not the only one. A buddy of mine had a 95 Mustang with the same problem. In all cases the rotors were replaced and the problem came back. For anyone to say that they have never seen warped rotors on a car, they are spewing Hoo Haa.

    Most of today's brake rotors are not made to be resurfaced either. In the old days, I would replace the rotors after every third pad change or at 90,000 miles. Unless you're driving a Swedish car like a Saab or a Volvo, or in my case, a Saturn L-Series, you don't often have that choice.




  7. #7
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    Re: Warped discs and other myths

    If you number a 4 or 5 lug hub and tighten number 1 lug to 80 foot pounds and number 3 to 100 foot pounds and number 4 to 75 foot pounds and take the car out and heat up the rotor to 300-400 degrees...the rotor will conform to the way the wheel lug has been tightened.
    This is how most Honda discs get warped -- by uneven lug nut torque.

    Chip H.

    Former owner: 2012 Honda Civic LX, 2006 Honda Ridgeline RTL, 2000 Honda CR-V EX, 2003 MINI Cooper S, 1992 Honda Accord LX, 1999 Mercedes ML-320, 1995 VW Jetta GLX, 1991 Mercury Capri XR2, 1981 Mercury Zephyr, 1975 Chevrolet Impala

  8. #8
    mrblanche
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    Re: Warped discs and other myths

    Just by the by, the brake expert I quoted up there, a guy named Pat Anderson and who goes by "brakemananderson" on the internet, gives 2 pieces of advice on braike mainenance.

    1. Torque all lug nuts by hand, with a torque wrench.

    2. Replace your brake flued on a regular basis by adding at the reservoir and bleeding at the wheel cylinders. Use only DOT4. This needs to be done at least every two years; every year is better, since brake fluid absorbs water, which reduces its boiling temperature and increases internal corrosion.

    He also suggest using DOT5 in hot rods, which solves a lot of problems DOT3 and DOT4 create.

  9. #9
    Senior Member Mase's Avatar
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    Re: Warped discs and other myths

    I had a 1987 Chevy Celebrity that seemed to need new rotors every time it needed new pads. Several different mechanics told me the rotors were too thin to be machined, they were warped, and had to be replaced. After a new set, braking would be fine for awhile and then it would get back to the throbbing/pulsing. I was never hard on my brakes in this car, and if I warmed them up with heavy braking, I would never keep my foot on the brake when stationary. Used the parking brake till the light turned green.
    A man's greatest mistake is to think he is working for somebody else.

  10. #10
    Vulture of The Western World Eric's Avatar
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    Re: Warped discs and other myths

    When I rebuilt the brake system in my Firebird (including all-new stainless lines, new master cylinder, calipers, wheel cylinders, etc.) I switched over to DOT 5 ...

  11. #11
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    Re: Warped discs and other myths

    --------------------------------------------------------------------------------
    >>I had a 1987 Chevy Celebrity that seemed to need new rotors every time it needed new pads. Several different mechanics told me the rotors were too thin to be machined, they were warped, and had to be replaced. After a new set, braking would be fine for awhile and then it would get back to the throbbing/pulsing. I was never hard on my brakes in this car, and if I warmed them up with heavy braking, I would never keep my foot on the brake when stationary. Used the parking brake till the light turned green.<<

    Use of a torque wrench would have prevented the warping of those rotors. That doesn't mean using it after the nuts are tightened with an impact wrench, but used as the tool to tighten the nuts alone. Run them down to finger tight and finish with the torque wrench!

  12. #12
    DonTom
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    Re: Warped discs and other myths

    I have had warped rotors on three cars, all of them Fords.

    I have not had that problem on my Fords, but did on an 1989 Caddy. But it was caused by overtightened lug nuts. Have you checked to see what torque the wheel nuts should be?

    The best way to screw up rotors is to overtighten the wheels. And it will take several weeks or longer before you notice any problem. And when you once feel it, the damage has been done. At this point it will not help to loosen the nuts. You need to replace the discs.

    -Don-



  13. #13
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    Re: Warped discs and other myths

    If you're very very lucky, re-torquing the lugnuts after the gorilla with the airwrench has been at them, can sometimes let the metal relax back to (or very near) it's original flatness.

    BTW: Passenger cars should be torqued to 70 lb-ft, which if you're using the wrench supplied with the car, is roughly your upper-body weight applied to the end of it.

    Which brings up another good point -- the airwrench gorilla isn't doing you any favors by overtightening the lug nuts. If you get a flat (at night, in a rainstorm, in a bad part of town), you might not be able to remove the wheel by yourself. And then you're really in trouble.

    Chip H.

    Former owner: 2012 Honda Civic LX, 2006 Honda Ridgeline RTL, 2000 Honda CR-V EX, 2003 MINI Cooper S, 1992 Honda Accord LX, 1999 Mercedes ML-320, 1995 VW Jetta GLX, 1991 Mercury Capri XR2, 1981 Mercury Zephyr, 1975 Chevrolet Impala

  14. #14
    Vulture of The Western World Eric's Avatar
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    Re: Warped discs and other myths

    "Which brings up another good point -- the airwrench gorilla isn't doing you any favors by overtightening the lug nuts. If you get a flat (at night, in a rainstorm, in a bad part of town), you might not be able to remove the wheel by yourself. And then you're really in trouble."

    Even worse, they're so over-torqued that they snap off when you apply the force necessary to loosen the lug. I've had that happen on a car with four-lug hubs; lost two studs - and had to drive home (fingers crossed) appx. 20 miles that way....

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