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rob's garage

Rob,

When I drive my Nissan Sentra I hear a squealing sound coming from the front of the car. But when I press the brake pedal the noise goes away.

This doesn't make sense to me - what do you think the problem is?

Robyn

Actually Robyn, this does make sense.

You have described a typical symptom of worn brake pads that are on the brink of needing repair. It is likely that your front brake pads have a "squealer" mounted on them. This is a thin piece of metal that easily wears away as it comes in contact with the brake rotor. It is designed to contact the rotor and emit this noise to let the driver know that the brake pads will require replacing very soon. The metal piece protrudes beyond the friction material of the brakes just enough to provide you with sufficient friction to stop your car safely.

Here are the most common reasons that the squeal goes away during a pedal press:

• Application force of the pads against the rotor changes the position of the squealer just enough to move the metal strip away from the rotor.

• The squealer harmonics can be dampened by the friction of the pads against the rotor.

• The caliper is not being held tightly in the caliper adapter. This can set up harmonics that manifest themselves as a squeal. Again, by applying the brakes, this harmonics is removed by the clamping and dampening effect of the applied brakes.

This metal is sacrificial so it will continue to wear away without damage to the rotor for now - but you need to get to a shop soon and have the brakes inspected. Caught soon enough, this problem will not grow to the point that will make you squeal as the repair shop reaches for your wallet to pay for a huge repair bill.

Send your questions for Rob MacGregor to globedrive@globeandmail.com

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