Brake Fluid Leak: Causes And Solutions

Brake fluid is an essential fluid in the vehicle’s braking system. It circulates throughout the circuit to transmit the pressure exerted on the brake pedal to the wheels for braking. It must therefore be available in sufficient quantity in order to preserve braking effectiveness. If brake fluid leaks, your braking system will no longer be able to function properly.

What is brake fluid?

Brake fluid is the fluid that is used in the braking system of vehicles. It is a synthetic product which has the characteristic of being incompressible over the time allocated to its use, which means that its volume must remain constant under the action of external pressure, and very little sensitive to temperature variations.

Brake fluid becomes compressible due to temperature, which produces vapor. This is a gas which, depending on its water content, will cause the brake fluid to boil. Due to changes in temperature and the presence of water in the liquid, the latter ends up losing its incompressibility properties and needs to be replaced.

Brake fluid is an integral part of the car’s brake system. It is even the heart of it. It has an essential function in the braking system. In fact, it spreads throughout the hydraulic circuit and allows, thanks to pressure on the pedal, to transmit the braking force to the four wheels of the vehicle.

When to bleed the brake fluid?

Your brake fluid must be drained regularly, at least every two years, otherwise you risk damaging the braking system and ending up, for example, with brakes that no longer respond.

Brake fluid is hygroscopic , meaning it has the ability to absorb moisture from the air. When the brakes are used, the brake pads rub against the brake rotors and cause the temperature to rise several hundred degrees. This high heat is transmitted to the brake fluid.

These temperature changes as well as the humidity in the air gradually degrade the brake fluid. Since brake fluid is hygroscopic, its boiling point drops considerably, from 230°C to 165°C.

In the event of repeated excessive braking, gas bubbles mix with the brake fluid, which may damage the brakes. It is therefore necessary to have the boiling temperature of the brake fluid checked regularly by a specialist. This also applies to drum brakes.

Brake fluid bleeding should generally be done every 50,000 kilometers . But above all, remember to change your brake fluid every time you replace your brakes.

The quality of brake fluid is important. It can be checked with a DOT index, allowing the liquid to be classified according to its resistance to heating. A DOT 3 brake fluid, for example, is often glycol-based and has a boiling point of 205°C.

Which brake fluid to choose?

To choose from the different brake fluids , follow the instructions of your car manufacturer, indicated in the driver’s manual.

Here are the brake fluids you may encounter:

• Mineral fluids , mainly used by Rolls Royce, and Citroën, on its older models, which use a single hydraulic system for the suspension, steering, brakes and gearbox.
• Synthetic fluids , made from glycol, which meet American DOT standards as defined by the Department Of Transportation. Depending on the standard granted to them and their appearance on the market in chronological order, they are referred to as DOT 2, DOT 3, DOT 4, Super DOT 4, DOT 5.1.
• DOT 5 silicone-based : does not absorb moisture and is therefore more resistant over time.

The most commonly used brake fluids today are DOT 4, Super DOT 4 and DOT 5.1 for synthetic fluids and DOT 5 based on silicones. With the exception of DOT 2, DOT 3, DOT 4, Super DOT 4 and DOT 5.1 liquids are miscible with each other.

How to detect a brake fluid leak?

A brake fluid leak is indicated on your car’s dashboard. A light representing a pedal lights up. After a prolonged stop, you will see a small stain on the ground under your car. The liquid has no odor or any particular color.

You can also detect a leak easily by regularly checking your brake fluid level . It costs you nothing and allows you to prevent any problems. Make sure the liquid level is between the minimum line and the maximum line. If the level drops too quickly, don’t wait to react.

Have you noticed a leak and want to measure its extent? Lay a newspaper under your car and see the size of the stain.

If you experience a brake fluid leak, you will notice the following symptoms:

• The brake fluid warning light display on the dashboard;
• A puddle under the vehicle ;
• A drop in the brake fluid level in the reservoir;
• An extension of braking distances ;
• A soft or digging brake pedal ;
• Clogging of the brake lining .

What causes a brake fluid leak?

Leaking brake fluid can lead to brake failure. So this is not a problem that you should take lightly. Here are the most common causes of a brake fluid leak:

• A problem with the bleeder screws : located at the level of the brake calipers, the screws are used to eliminate excess fluid when maintaining your braking system.
• A faulty master cylinder : This part sends brake fluid to the braking system via hydraulic lines. If it is defective, then fluid accumulates in the rear of the engine compartment.
• A defective wheel cylinder : brake fluid can then be observed on the sidewall of your tires.
• Wear of pistons or hoses .

What is the price to change the brake system?

If you notice a brake fluid leak, look where it is located: the rear or front of your car. Depending on the case, it is possible to change the front or rear brake kit, depending on the location of the fault. Obviously, the price of this kit varies depending on the model of your car, but count on average €200 to repair a brake fluid leak.

Here is an overview of the prices for a rear brake kit:

And there you have it, you know everything about brake fluid and the risks of a leak! If your car exhibits symptoms of a brake fluid leak, go to the mechanic without delay.