Dear Ask a Mechanic,
I have a 2004 Mazda 6 with very low mileage, about 60,000 kilometres, and in pretty good working order. The only issue is when I drive in reverse and step on the brake. There is a peculiar squeal (it sounds like a wounded animal). My mechanic assures me there is nothing wrong with the brakes. Any suggestions on what could be causing the noise. – Squealing Brakes
Brake noises are the nemesis of many mechanics. There are plenty of obvious causes for squeaks, squeals or grinds, but if you inspect the brakes and nothing is seized, rusty or worn out, the source of these unwanted sounds can be tough to pin down.
The cause could just be due to what material the brake pads, and to a lesser extent the rotor, are made from. Inexpensive brake parts (and those meant for performance use) are prone to squealing when they are used.
The shims and retainers, as well as the dust and heat shields that are often behind the brakes, can all cause noise. Parts of the rotors and drums, areas not swept clean by friction like other parts of the brakes, can swell with rust and touch up against each other. This may only occur when they get hot, or when your vehicle is making a turn, as the wheel bearings will ever-so-slightly deflect.
Glazed rotors (or brake drums) can also result from excessively hard use and from infrequent or gentle use. In the latter, the wear surface lightly corrodes from ambient moisture while sitting, and then is polished off by the friction, becoming very hard and very smooth. Squealing, shuddering and loss of “bite” (resulting in greater braking effort being needed) can all result.
Because your Mazda is an older vehicle with very low mileage, there are additional possibilities. As vehicles age, rubber bushings in the suspension either harden, or – in vehicles that have been heavily undercoated or have appreciable oil leaks – soften and deteriorate. This can amplify sounds and vibrations. In some cases, the material hardens with time or even corrodes from the backing material. I’ve also seen pad material become saturated with undercoating overspray.
With only slightly less mileage than your Mazda 6 at 50,000 kilometres, the rear brakes in my mother’s 2009 Hyundai Sonata have recently developed a loud and annoying “moo” and accompanying vibration just as it comes to a stop. Her brakes aren’t even half worn yet and work fine otherwise. But I will still replace the pads and rotors with new ones when I do her seasonal tire change this fall, solely to banish the nuisance noise.
I suspect it’s a similar situation with your brakes. Your mechanic is likely telling you the truth that your brakes are fine. The solution is probably just new pads and rotors.
Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to firstname.lastname@example.org. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.
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