Chattering Brakes at High Speed

Discussion in 'The Garage' started by GWestphal, Sep 11, 2012.

  1. GWestphal

    GWestphal Golden Member

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    2000 Buick Century sedan.

    When braking at 50-70mph, car vibrating brake chatter, frequency slows as the vehicle slows.

    When braking at slower speeds it is fine.

    I'm assuming it is either the rotor or brake caliper related since it only occurs when I'm braking. Started after I had the bearings in the left rear wheel replaced.

    A warped rotor? Loose lugs? Bad Tie rod? CV joint?
     
  2. SyndromeOCZ

    SyndromeOCZ Senior member

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    Sounds like it could be a warped rotor, if you can see through the wheels then check to see if there are spots on the rotor that look different. I don't have the words to explain but you should be able to see it with your eyes if they are warped very bad.
     
  3. AMCRambler

    AMCRambler Diamond Member

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    Do you feel it in the brake pedal? Or is it just the seat of your pants feeling of the car shuddering. Could be they damaged some suspension components in the back or something has come loose.
     
  4. Costas Athan

    Costas Athan Senior member

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  5. Doppel

    Doppel Lifer

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    Nonetheless, the rotor is regularly a source of vibrations, be it through build up or material or whatever and it does present in the way the OP describes.
     
  6. CraigRT

    CraigRT Lifer

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  7. Costas Athan

    Costas Athan Senior member

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    Yes, but if the vibrations are caused because of DTV which is caused by excess run-out, replacing rotors won't solve the problem. According to EBC the problem will reappear soon after 3000 - 4000 miles.
     
  8. GWestphal

    GWestphal Golden Member

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    I don't know if I can differentiate between brake pedal and whole car shaking. It's pretty high amplitude vibration to the point where I'm going to have it brought in a looked at when I rotate my tires and get a new wind shield wiper pump this weekend. I hate putting money in a car when it's only worth like $1,200...
     
  9. Costas Athan

    Costas Athan Senior member

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    Does the steering wheel vibrate under braking?
     
  10. GWestphal

    GWestphal Golden Member

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    Yes, it does. Though whether that is from the whole car shake or something working it's way through the rack and pinion is uncertain?
     
  11. Costas Athan

    Costas Athan Senior member

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    If it happens under braking a common cause are the front rotors themselves.
     
  12. GWestphal

    GWestphal Golden Member

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    Found a good mechanic, turned both front rotors for a measly $45. Drives or rather brakes like a dream. It's funny how 1/100th of an inch can make that much of a difference.
     
  13. phucheneh

    phucheneh Diamond Member

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    Saying 'no such thing as warped rotors' makes you look like a fool and/or pompous ass. IMO. (edit: no offense, just a pet peeve. correcting known, common vernacular to appear more intelligent, that is)

    Yes, it's generally 'thickness variation' that causes pedal pulsation, not warpage. But there is no guarantee that both sides of the rotor will wear identically...which would result in, yes, warpage, as well. Then you've got your problems like hard spots/heat checks.

    Solution is always the same: turn rotors if possible, replace if not. Then learn better driving practices.
     
    #13 phucheneh, Sep 17, 2012
    Last edited: Sep 17, 2012
  14. Costas Athan

    Costas Athan Senior member

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    According to Stoptech's article actual cases of warped rotors are extremely rare! The link is available in one of my previous posts. Read it yourself. EBC backs up Stoptech's article.

    And I don't think that the problem occurs because the sides of the rotor don't wear identically. It happens because thinner spots appear on the rotor due to excessive run out.
     
  15. Howard

    Howard Lifer

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    So your understanding is that a thickness variation is equivalent to warpage?
     
  16. phucheneh

    phucheneh Diamond Member

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    I read both articles long ago.

    Drive a car with severe pulsation, then chuck the rotors up on a quality lathe.

    As the lathe turns, you'll want to ease the bits in, near the center of the rotor, until they faintly touch. You'll hear a little rythm as the bits come into and out of contact with the rotor surface.

    Move the cutting head in to the edge of the rotor surface (torwards hub). Turn the bits in another thousandth or two, and run a quick fast cut.

    You will likely see that only part of each side of the rotor gets machined. There will be a shiny patch that the bits were not able to touch as the rotor spun. This patch will likely not be in the same place on both side of the rotor.

    Is that not what one would define as 'warped?'

    Again, the simple thickness variation is more to blame for what you feel in the pedal (or the whole car, if it's bad enough). But 1) it's still splitting hairs to say that's not a 'warped' rotor and 2) the rotor probably DOES have some warp, anyway. (edit: again, defending on how you define warp.)

    I don't even generally disagree with those articles; the Stop-tech one is very familiar and has some good info. But all that really needs to be said is that vibration under braking is generally caused by some kind of quality of misshapenness that the rotors have acquired. And since the industry standard is to just say 'warpage,' there's no point in sounding off with an 'Actually...' comment.

    The more important thing for people to learn is WHY rotors...become misshapen. And that, in a word...okay, two words...heat and pressure (does 'and' count? okay, three words).
     
    #16 phucheneh, Sep 18, 2012
    Last edited: Sep 18, 2012
  17. Costas Athan

    Costas Athan Senior member

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    Well that's the definition:

    And I think that the word is used to declare that a rotor has curved because of abrupt cooling. In this case I don't think it suitable for DTV or other rotor problems that cause vibration.
     
  18. phucheneh

    phucheneh Diamond Member

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    I'm gonna feel stupid, probably...but 'DTV'? I can't de-acronymize that one off the top of my head. Guessing the 'TV' is thickness variation.

    The 'argument' comes because 'warp' simply conjures up different images for different people.

    Forgive my quick sketch, but basically:

    [​IMG]

    You're looking at the outer edge of the rotor, torwards the hub ring. People want to say rotors don't 'warp' because they don't do what you see on the right- bend around like a vinyl record left out in the sun. The left would of course be your 'thickness variation' illustration. By the dictionary definition, both the inner and outer surfaces of that rotor have warped.
     
  19. SkullWalker

    SkullWalker Member

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    How much do two new rotors cost...?
     
  20. Costas Athan

    Costas Athan Senior member

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    Yeah, EBC uses the acronym. Disk Thickness Variation.

    When the run out is over the limit, some spots of the rotor make constant contact with the pads even when the brake pedal is fully released. That makes these spots thinner and as a result the rotor surface uneven.

    When a rotor gets warped because of heat issues I'm not so sure that it gets so many curves as you have illustrated them. Maybe it's just a single bent... Anyway, it is my understanding that we use the word "warped" when the disk gets an uneven surface because of heat issues.

    In both cases of course the aftermath is a disk with uneven surface, but the mechanism is different. And also the solution is different. If it is warped because of the heat a disk with a better heat resistant material would be the solution. But if the problem is DTV even if the disk is replaced with an expensive one the problem would appear again, because the cause is the excessive run-out and the chances are that something (like the hub for example) is causing it.
     
  21. phucheneh

    phucheneh Diamond Member

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    The little sketch was a BIT exaggerated. I agree, in most cases it's simply that one half of the rotor (divided radially; not comparing inner/outer) is thinner than the other. This is evidenced when you watch the rotor get machined in very small increments, as mentioned earlier.

    However, I'm not sure what you're talking about at the end there. 'Thickness variaton' is not due to a faulty hub bearing.

    When measured with a dial indicator, both thickness variaton and any other type of term you want to use for uneven wear to one side of a rotor will cause excessive runout measurements.
     
  22. Costas Athan

    Costas Athan Senior member

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    You are wrong. The run-out could be caused by geometry issues of the hub or I don't know which other parts of the arm of the suspension.

    Read here --> http://www.ebcbrakes.com/automotive/pro_cut_lathe.shtml

    And Brembo agrees with EBC's opinion: http://bremboaftermarket.com/en/car_disc_catalogue/Instructions_Installation.aspx In paragraph 8 it states that run-out should be measured with the rotor fitted on the car. That's because not only the rotor itself could be the cause of run-out. (I think its rare because rotors are precisely machined).

    Look that video posted by DBA --> http://www.youtube.com/watch?v=3ZjoBaCfeNg The mechanic checks hub's run-out seperately before it proceeds to check the run-out with the disk fitted.
     
  23. phucheneh

    phucheneh Diamond Member

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    uh, ok.

    I didn't say measured runout in a brake rotor COULDN'T be caused by a hub bearing with play in it. Or simply a hub that has, say, been tweaked by an impact.

    I meant more that 1) I didn't understand exactly what you were trying to say and I can now also add 2) If you're troubleshooting a brake pulsation problem, 'excessive hub runout' is unlikely to be a problem. I've seen people machine rotors without success, but in the end, new rotors always fixed the brake pulsation. Implying either the tech or equipment was to blame, or that the rotor had simply been damaged too greatly. Those little funny-colored specs that basically indicate a random change in metalurgy can be awfully hard to turn down with even the sharpest of bits.

    But not once, literally not one single time, have I seen a car with a brake complaint end up needing hubs. The exception would be when a service advisor writes 'brakes grinding' and you test drive only to find out that there is a hub(wheel) bearing that is so destroyed that it sounds like you've run over Oscar the Grouch and are dragging him as well as his abode beneath the car.