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car shudders when brakes applied

edited November -1 in Repair and Maintenance
I have a '95 chevy lumina and the car/steering wheel shudders when the brakes are applied (frequency varies with speed). What could this be? I want to fix it myself but I just need a diagnostic of what is wrong.
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Comments

  • edited June 2007
    The most obvious cause would be warped brake rotors, but there are also other things it could be.
    Worn suspension parts such as ball joints or tie rods can cause this and so can loose wheel bearings.
  • edited June 2007
    Is it easy to tell by visual inspection if the rotors are warped?
  • edited June 2007
    Often you can't tell just by looking. It doesn't take much warpage to cause braking shudder, and if you actually could see it the disc would definitely be ruined.

    You'd have to use a special runout gauge on the disc to see if it's warped, and how badly.

  • edited June 2007
    No. You need a special gauge, called a dial indicator, that mounts to the brakes and has a needle that scrapes along the rotor surface. You zero it when the needle is just touching the rotor. Then spin the rotor slowly. The gauge reading will fluctuate if the rotor surface is not perfectly smooth, this is called runout. If the runout as shown on the gauge ever exceeds the maximum allowable amount (a Haynes manual will have these specs) then the disc can be considered warped and will have to be machined or replaced.

    With rotors getting thinner and cheaper, it makes more sense to just replace, rather than machine.

    If you don't want to buy the dial indicator, then take it to a shop. They'll test them for you.

    -Matt
  • edited June 2007
    Correction, you set it half an inch from the rotor, then zero it.

    Otherwise you'll miss warpage in the direction opposite of the needle.

    Just correcting that bit of misinformation.

    -Matt (again)
  • edited June 2007
    Sometimes it can be a combination of brakes and another problem in the suspension or wheel bearings.

    Replace the brake pads and machine/replace the brake rotors and everything may be fine at first.
    What can happen after a while is that the new rotors may warp a few thousandths of an inch. While you may not even normally notice this in most cases, if you have a loose wheel bearing or suspension part this small amount of warpage will be magnified and made to feel worse than it actually is.

    The front suspension should be checked along with the brakes.
  • edited June 2007
    It is most likely warped rotors.
  • edited June 2007
    so I guess my next quesiton is, how do you "check" the front suspension?
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