Pulsating noise when braking at low speed - Cause?

[Le Dérisoire]

I'm well aware this is not a mechanics forum, but it doesn't hurt to try.

Car: Hyundai Accent 2009 - 110000km - No ABS

Problem: For several months, I have been hearing a pulsating grinding noise when I brake at low speed (- 30 km/h). The sound matches the wheels rotation speed, meaning that the pulsation gets slower (and louder) as the car slows. I do not hear any sound when braking at higher speed (+ 30 km/h) or when I'm not braking at all.

The sound is coming from the front brakes. I know that because when I stop the car using the handbrake there is no sound (the handbrake uses the rear brakes only).

What it's not: It's not the brake pads and rotors. I know that because that's what I thought at first so I changed the brake pads and rotors yesterday (they were quite old anyway). The sound is till there just as before.

Any ideas? Yes, I will go see a mechanic if I can't find the answer myself.

Thanks!

[Jack]

Maybe the wheel bearings are worn, causing the brake rotors to wobble with respect to the calipers?

[sisto]

You could also have a bad caliper. Did you check them when you replaced the pads and rotors? Also did you lube the pins? Does the car pull left or right upon braking. Lastly this could also be a trans-axle. Check to make sure all of the boots are intact. If not that's likely the cause. If you can change the pads and rotors you are likely able to do an axle too. Good luck and keep us updated.

[Spork]

Maybe the wheel bearings are worn, causing the brake rotors to wobble with respect to the calipers?

You can check the runout with a dial gauge and a magnetic stand. 

[sokoloff]

The sound is coming from the front brakes. I know that because when I stop the car using the handbrake there is no sound (the handbrake uses the rear brakes only).

Note that if the rear brakes are discs with integral drum brakes for the parking brake, you may have reached the wrong diagnosis.

[Le Dérisoire]

Additional info:

• sokoloff: The rear brakes on that car are drum brakes only.
• sisto: Yes, I checked the calipers. They seemed fine to me, but I'm not an expert. Also, one of the caliper pin was a bit difficult to move. I lubed them all with anti-seize when changing the pads and rotors and it's fine now. The car does not seem to pull to the left or right when braking.
• I accelerated in reverse and used the brakes a few time. No noise! So, there is only noise when braking while the car goes forward! Weird, right?

Based on your answers, possible problems are:

• Bad caliper (although they look fine)
• Worn wheel bearing
• Damaged boots

For now it's only an annoying noise. So, when I will put winter tires this fall I will try to check those things. If I still can't find the problem, I will either do nothing until it gets worse or see a mechanic. We'll see.

Thanks! If you have anything to add, don't hesitate!

[Goldielocks]

I had a grinding / pulsating noise from my wheels,   afraid it was the bearings. 

Good? News....It was a rusted out backing plate, and the remaining material was quickly cut off for free, no point replacing.

[Papa Mustache]

Backing plate ducts air across the rotor and protects it from splashes. I have a car without backing plates too.