How to diagnose disc brake problems

Written by chris stevenson
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How to diagnose disc brake problems
Disc brakes can warn the driver when they are worn or failing. (brake calipers image by Tom Oliveira from Fotolia.com)

Any brake component suspected of faulty operation needs to be inspected immediately. The front disc brake pads on newer vehicles have their own peculiar warning signs, and being able to read them early enough can reduce repair costs down the road. The front disc brake pads provide most of the stopping power for the vehicle and can actually wear out faster than the rear brakes. Disc brakes can show some early warning signs of failure if the vehicle owner knows what to look for.

Skill level:
Moderate

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Things you need

  • Floor jack
  • Jack stands
  • Tire iron

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Instructions

  1. 1

    Check the dashboard for a brake warning indicator light. Faulty brakes will sometimes show up on your dashboard via a trouble code. Consult a trouble code book or an online resource to determine the type of brake malfunction involved. This type of warning light requires immediate attention.

  2. 2

    Listen for any unusual sounds coming from the brakes under normal driving conditions. Disc brakes that have worn or become overheated make a variety of noises. When brake pads have overheated and become glazed, they will make a squeaking sound when they're applied, and this can be most noticeable during very slow stops. Disc brake pads that have worn past their lining limits will make a louder swishing, grinding or howling noise when the brakes are applied. This sound will be present at all times during braking, and sometimes a slight vibration can be felt in the steering wheel.

  3. 3

    Shift the vehicle into park and set the emergency brake. Loosen the lug nuts on one wheel. Lift the vehicle in the air with a floor jack and secure it on two jack stands placed under the frame next to the front wheels. Finish removing the lug nuts, remove the wheel and set it aside. Carefully examine the pad thickness between the calipers. Make sure to inspect the inside pad since sometimes it wears out faster than the outer pad. Disc pads that have worn down to their rivets or have worn past factory specification limits must be replaced. Both inner and outer pads should be replaced on both front wheels, even if only one side has worn considerably.

  4. 4

    Examine the disc rotor carefully. It should have a smooth, clean and shiny surface. There should be no striations or grooves in its surface. Deep grooves, sometimes appearing as parallel lines, will indicate that the rotor surface has made contact with the pad rivets, which shows excessive wear over a longer period of time. Deep grooves in the brake disc rotor can cause lock-up and brake shimmy, accompanied by a loud grinding noise during hard braking. Disc rotors have a minimum thickness requirement and must be measured with a micrometer. Any grooved disc rotor must be removed and turned on a lathe or replaced if too much metal has worn away.

  5. 5

    Inspect the brake caliper. The caliper holds the brake fluid that exerts pressure on the pads to grip the rotor. The piston inside drives the pressure, but it has seals to keep the fluid inside the caliper piston bore. Any brake fluid leak around the rubber boots inside the bore means that the seals have worn. Brake fluid will contaminate the pads, causing slippage, glazing and burning. Such a leak requires the calipers to be rebuilt or replaced if severely damaged.

Tips and warnings

  • Do not drive a vehicle that has obvious brake noise or a pedal that goes all the way to the floor. Have the brakes inspected or repaired immediately.

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