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Steering wheel vibrates under firm braking

Discussion in 'A3/S3 Forum (8L Chassis)' started by hfu, Jul 7, 2004.

  1. hfu
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    hfu Member

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    [Jul 7, 2004]
    I get some vibration under hard braking... should this be happening?

    I guess not!!!
    If not, whats the problem?
    #1
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  3. Gambba
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    Gambba Active Member

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    [Jul 7, 2004]
    It maybe that your discs are warped and need replacing.

    If you don't feel any abnormal vibration when driving without braking then it's unlikely anything to do with wheel bearings, drive shafts etc, and I would trongly suspect the discs. The standard discs aren't up to much in my eyes, but a lack of torque on wheel bolts will warp the discs and is probably the biggest cause of failure.
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  4. MingBluS3
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    MingBluS3 Member

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    [Jul 7, 2004]
    yep second that, you must have overheated them.
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  5. recomdos
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    recomdos Member

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    [Jul 7, 2004]
    think mines doing the same /ubbthreads/images/graemlins/frown.gif
    #4
  6. EvilTad
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    EvilTad Member

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    [Jul 7, 2004]
    Are your tyres ok?

    when they start to go off and get bald, they start vibrating.

    Thats whats happened to me recently. New tyres and its all fine again.
    #5
  7. imported_alwinharrison
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    imported_alwinharrison Guest

    [Jul 7, 2004]
    Try taking your motor to your friendly local MOT station, and ask them to do a roller brake test.

    Warped discs will show up on the rollers.
    #6
  8. peteA3tdi
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    peteA3tdi Member

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    [Jul 8, 2004]
    [ QUOTE ]
    neil.c said:
    I don't think warped brakes will show up on an mot test

    [/ QUOTE ]


    warped brake discs will show on brake rollers and are a mot fail
    #7
  9. neil.c
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    neil.c Senior

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    [Jul 10, 2004]
    I don't belive mot brake test equipment spins the wheels fast enough to show up warped disks
    How would it show up warped disks when it is measuring brake force?
    This would be the same whether the brakes were warped or not.
    #8
  10. imported_bayliss
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    imported_bayliss Guest

    [Jul 10, 2004]
    it would only be noticable when the discs are BADLY warpped.
    #9
  11. imported_bayliss
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    imported_bayliss Guest

    [Jul 10, 2004]
    i think the only "real" way to find out if it's the discs, is to remove them, and take them to a machinst; the kinda place that would skim heads etc - they would have something perfectly flat (probably laser) and could tell that way.

    hope that helps

    PS have you looked at the the suspension arm bushed hopsta mentioned Wed Jul 07 2004 ??
    #10
  12. HTC
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    HTC Active Member

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    [Jul 11, 2004]
    You can check if you're discs are warp very easily with a dial test indicator.

    Remove the wheel and attach the DTI to the hub or caliper (they are usually magnetic). Then turn the disc by hand and see if the DTI shows any fluctuation.

    Or remove the disc and get a straight edge on it.
    #11
  13. neil.c
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    neil.c Senior

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    [Jul 11, 2004]
    You can check if the disks are warped with feeler guages. If you work the guages between the fixed caliper carrier and the disk, then rotate the wheel slightly and repeat with the feeler guages. When you have worked your way through 360' you will get a map of how true the disk is running in relation to the brake caliper
    #12
  14. HTC
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    HTC Active Member

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    [Jul 11, 2004]
    Yeah, that'll work too :)
    #13
  15. peteA3tdi
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    peteA3tdi Member

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    [Jul 11, 2004]
    [ QUOTE ]
    neil.c said:
    I don't belive mot brake test equipment spins the wheels fast enough to show up warped disks
    How would it show up warped disks when it is measuring brake force?
    This would be the same whether the brakes were warped or not.

    [/ QUOTE ]

    when doing a roller brake test on a MOT you check the wheels one at a time slowly pressing the brake till max braking force is seen as you are doing this if the disc/disc's are worped when you get close to the max force you will feel and see the run out, it need's to be over about 40kg braking force to fail
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  16. neil.c
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    neil.c Senior

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    [Jul 11, 2004]
    Yeah that makes no sense because you test the wheels in axle pairs with two guages one for the left wheel and one for the right, test one then the other then both together.
    You look for balance between the two.
    What does 40kg mean?
    #15
  17. imported_alwinharrison
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    imported_alwinharrison Guest

    [Jul 11, 2004]
    Believe me if your disc are warped enough to cause judder at speed, then it WILL show up on a roller brake tester as used for carrying out MOT Testing.

    Yes they run at low speed, but they are very sensitive.

    Pressing the pedal part way down and holding steady will show a reading of brake force on the relevant meter Any disc runout will show up as a fluctuation of the meter reading.The operator can run both wheels together, or each one individually.

    The meters register brake force in Kg, and a fluctuation due to warped discs could be a variation in reading of 40kg with the pedal held steady.A much lesser fluctuation reading would still be felt as a judder when braking at speed.

    As Pete TDI says you can both see the runout on the meter, and feel the movement on the pedal when a steady application of the brake is made.

    I have used one of these machines for years up to recently, and have successfully used it for diagnosing many cases of warped discs.
    #16
  18. neil.c
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    neil.c Senior

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    [Jul 11, 2004]
    Thanks, your post makes sense Alwin unlike Pete's. The problem is that most modern cars have floating calipers which are designed to follow the disk. Also most MOT testers don't seem to take enough time on the brake test to find this and 40kg would be some seriously warped disks.
    #17
  19. leespears1
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    leespears1 Member

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    [Jul 12, 2004]
    take it 2 kwik fit- free brake tests etc...
    #18
  20. peteA3tdi
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    [Jul 12, 2004]
    [ QUOTE ]
    neil.c said:
    Thanks, your post makes sense Alwin unlike Pete's. The problem is that most modern cars have floating calipers which are designed to follow the disk. Also most MOT testers don't seem to take enough time on the brake test to find this and 40kg would be some seriously warped disks.


    [/ QUOTE ]

    they need to be seriously worped to fail a MOT

    thanks alwin for making it clearer i'am dislecksick(word blind/can't spell)
    #19
  21. DavidR
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    DavidR Active Member

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    [Jul 12, 2004]
    More than likely the discs are perfectly true, but uneven brake pad deposits cause the vibration you feel especially if it is mild and most noticeable at speed. I have had some problems with uneven brake pad deposits on my stoptech rotors recently and having previously beleived the masses that my discs might be warped, I thought the only solution was machining, skimming or rotor replacement. In fact this is not the case, as a moderate and fairly new vibration can be cured by fitting agressive and abrasive pads, performing a few quick stops using the aggressive pads cold, and not allowing them to heat up and transfer more pad material. Basically this info is all on the stoptech website, but having bought some Hawk 9020 racing pads and tried their advice, the brakes are prefectly smooth without hint of the previous vibrations.

    This explains also a problem with the brakes on my previous car. Having used them without proper bed in procedures and then quite harshly on the road, the car developed a vibration. A track session with some red stuffs fitted smoothed out the vibration completely....

    Buying a set of "scrub pads" is a cheaper option than continuously skimming or replacing the disc, however, careful bed in and attention paid to cool down seems to avoid further issues.
    #20

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