If you hear a squealing sound coming from the wheels next time you hit the brakes, don’t ignore it. That sound could be an audible sensor on the brake pads - opens in new window or tab., letting you know that it’s time to replace them. Overly worn brake pads can score the rotors - opens in new window or tab.. While mild scoring damage can usually be machined out, rotors with deep scratches or warping need to be replaced.
Ceramic Disc Brake-Pad Set for Subaru
The audible sensors aren’t the only cause of brake squeal. On disc brakes, the noise can also be caused by the friction material used in the pads, which in some cases causes vibration that we hear as a shrill squeal. Try changing to a ceramic or premium metallic pad and see if the vibration and hence the squeal goes away. See “Easy DIY: Change Your Brake Pads - opens in new window or tab..”
The other solution is to apply Brake Quiet - opens in new window or tab., a product that acts as an adhesive holding the pads to the pistons, preventing them from vibrating and making noise.
Brake Feel
Unusual brake pedal feel is another indicator of brake system problems. The brakes are a closed hydraulic system that works by transferring hydraulic power into wheel cylinders - opens in new window or tab. that cause the brake pistons to move pads, putting pressure on the rotors. The friction between the brake pads and rotors brings the car to a stop.
If the brakes are working properly, the brake pedal should feel firm when you depress it. If the pedal feels spongy, it could mean one of these things:
- air has gotten into the brake lines
- a brake caliper’s piston seal is starting to leak
- the master cylinder - opens in new window or tab. located under the hood next to the firewall is worn out and started to leak
- the brake lines are damaged
A possible solution is to apply Brake Quiet.
Repair Tips
If the pedal seems unusually low when you depress it, the cause could be a worn or improperly bled master cylinder, air in the system, or too much play between the brake pads (or shoes) and rotors or drums. Start by inspecting the master cylinder and brake lines for leaks. Make sure the master cylinder is properly bled, to eliminate any air in the lines. If this doesn’t fix the problem, suspect the brake assemblies at the wheels.
Sometimes the fix is simple. If you or another person who drives the car routinely like to feather the brakes, you might not be braking hard enough to actuate the self-adjusters that adjust the distance between the rotors and pads as the pads wear. A few hard pumps on the brake pedal might fix the problem.
If your car is equipped with antilock brakes, be aware that the brake system operates under extremely high pressures. Before opening the system up to perform any repairs, follow the shop manual instructions about powering down the accumulator to release system pressure.
Brake fluid can become contaminated by dirt in the atmosphere and water, so it’s important to bleed the system - opens in new window or tab. down thoroughly before refilling it with fresh brake fluid. The fluid recommended by the Department of Transportation (DOT) recommended fluid should be listed in the shop manual. Silicone brake fluid - opens in new window or tab. is more resistant to heat and hard service on a racetrack than glycol fluid. (But it’s important not to mix the two.)
Evacuate and refill the braking system according to the manufacturer’s recommendations for best performance.
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This article is meant to provide general guidance only. Automotive maintenance, repair, upgrade, and installation may depend on vehicle-specifics such as make and model. Always consult your owner's manual, repair guide for specific information for your particular vehicle and consider a licensed auto-care professional's help as well, particularly for advance repairs.