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Brakes are one of the essential parts of a car, especially regarding your safety and the safety of other cars around you. 

If you hear a squealing noise every time you apply brakes, and it has been a long time since you had a brake service, then it is time to check your car for dirty brake fluid. 

When you press down on the brake pedal, pistons push brake fluid to the calipers, and the brake pads are compressed onto the rotor. 

As brake fluid ages, it can lose its viscosity and becomes thick and less effective. It can also absorb moisture which causes squeaking noises when applying pressure. You’ll need to have the brake fluid flushed and replaced.

Brakes are usually made to bear the worst forms of abuse, but certain things may cause the brakes or certain parts to get affected by factors beyond the manufacturer’s control. 

This causes the brakes to behave differently, resulting in squealing noises, grinding, or ineffective braking.

Let us explore what might be causing the problems with your brakes, starting with dirty brake fluid.

Reasons Brakes Might Squeak Or Squeal

Dirty Brake Fluid

Braking is a closed system to avoid contact or contamination, but brake lines – made from rubber or stainless steel – carry the brake fluid from the reservoir to the calipers and back.

These brake lines are exposed to heat, dirt, water splashes, and other environmental factors that might cause them to wear down or damage. 

This wear or damage may cause the brake fluid to get contaminated with water, dirt, air, or other contaminants.

This causes the brake fluid to be distributed or moved unevenly within the system, and that causes uneven pressure on the brake pads when the brake is applied. 

This uneven wear of the brake pads may cause some part of the frictional material to wear more in some places, which may cause the squealing noise. 

Brake pads have a wear indicator mark, which is usually etched at the 75% of the total frictional material. Once the frictional material has worn away by 7

Since the brake fluid is dirty, the 75% mark may be reached in some parts of the brake pad, causing the squealing noise even though the remaining brake pad is less than 40% worn.

How To Check?

Brake fluid is usually a clear and transparent color. Check the brake reservoir under the hood for discoloration or particles in the brake fluid. Dirty brake fluid causes it to start burning or boil off after continuous braking, which may reduce the overall level of the brake fluid.

Brake fluid reservoir

How To Fix It?

There is a marking on the reservoir to show if the fluid level is adequate or not. But, before topping off, check the brake fluid for changes in color and transparency. Check the brake lines for wear and tear and any leakage when the brake pedal is pressed or pumped. 

After that, you will need to change or have your brake pads changed, and you are good to go. It is better to change the dirty brake fluid because if there is any water inside the brake lines, it may cause corrosion in the bores of the calipers and cause the calipers to lock up and make the brakes stick. 

If you carry on driving with dirty brake fluid, you could damage brake rotors and other braking system parts. This will reduce the brakes’ effectiveness, sometimes even making it feel spongy. 

This is because contaminants are causing the pressure before the brake fluid is affected and moved to the correct positions instead of the brake fluid compressing.

Rusted Brake Rotors

You hear a squealing or grinding noise every time you apply brakes. This is usually because of the brake rotors getting rusted from the water. Rusted brake rotors are also typical if cars are parked for days in moist locations. Most brake rotors are made from cast iron.

How To Check?

The brake rotor is visible behind the wheel of a car, and you can just look behind it and see a huge shiny disc. If there is rust, it will not be as shiny but will have a spotted and dotted brownish appearance.

How To Fix It?

You don’t need a brake service to fix it. You can remove the wheel and sand down the brake rotor yourself. Apply brake grease to keep the moving parts of a brake, such as calipers, bushings, etc., completely lubricated. 

Another way to remove this surface rust is to find an isolated low-speed road, get your car up to the allowed speed and apply between 15-20% brakes. The brake pad friction will rub away all the rust within 5-10 minutes of driving.

Backing Plate Touching The Rotor

The backing plate is one of the “unsung heroes” of a car part. Brake rotors are vulnerable to almost everything on the road, from water, small stones, heat, and brake pad material which comes off as brake dust. 

The backing plate protects the calipers and brake rotors from all this every time you press down on your brake pedal. All this abuse and sometimes misalignment of caliper pins or dirt on the rotor may cause a squealing noise every time you drive. 

This can also be caused by rusting between the knuckle assembly and the brake rotors. This forces the backing plate away from the assembly and rubs against the rotor.

How To Check?

Raise the car and remove the wheel. Next, spin the rotor and observe the distance between the rotor and the plate while shining a flashlight from the opposite end. 

If the backing plate touches the rotor, there will be visible contact points, and you may see pad debris falling off.

How to Fix It?

The backing plate is usually soft enough to be pushed or pulled by hand. If there is an area that you can’t get to this way, use a screwdriver and push the backing plate away. You can use the pointy side against the rotor to support the screwdriver. 

The backing plate and the brake rotors are made from robust materials. You can not simply damage them by hand, so keep working on it until all the squealing noise disappears because changing the backing plate might set you back $100.

Worn Brake Pads

Brake pads will always fade due to friction. The squealing noise can mean your brake pads are worn. When the brake pad material is worn away to the 75% mark, the brake pads start producing a squealing noise as an indicator of its condition. 

Over time, brake pad friction can cause the brake pad material to wear away completely and damage the brake rotor. 

This also produces heat which may cause the brake fluid to start boiling and damage the brake lines as well, and you will eventually notice that your brake fluid is low. When the fluid is too low, a light comes on in your car’s dash.

Discover telltale signs of low brake fluid in our Signs of Low Brake Fluid article.

How To Check?

There is always a mark carved in the brake pad material. This mark indicates that the brake pad is worn by 75%. 

Check for the mark once you hear the squealing. If you see the indicator and have squealing, then this is probably the time to schedule a brake service or do a brake service yourself.

How To Fix It?

Brake pads usually cost between $35 and $120, with labor ranging from $70-$130 per axle. The brake service must be done right. There are steps like applying brake grease, which, if not done right, may cause ineffective braking or brake failure. 

Always remember that brake service should include greasing, sanding the brake rotors, cleaning the calipers, and much more. 

If you are unfamiliar with the different parts of a braking system or the important steps, seek help or get your brake serviced professionally.

In Conclusion 

Dirty brake fluid can cause the hydraulic braking system ineffective and not apply pressure evenly on the pads to connect with the rotor. Without uniform pressure, the pads can bounce off the rotor or get stuck on one section and cause the squealing noise you are hearing.

Brake fluid should be changed every two years or 24000 miles. It is best to flush through the system to remove any contaminants from the system before filling it up with new fluid. A brake fluid flush is often missed, but you could find dirty brake fluid sooner if you don’t take this step before adding new brake fluid.

Brake fluid doesn’t evaporate, so if you see a decrease in fluid in the reservoir, you either have a leak or dirty fluid penetrating through the brake lines. More common is moisture finding its way through the lines into the brake fluid, which reduces the effectiveness of the fluid as it becomes less concentrated.

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