Q: How Does Brake Fluid Work?

asked by on

How does brake fluid work?

Brake fluid is a specialized type of hydraulic fluid whose properties are designed to provide pressure transfer to operate the brake while dissipating the heat developed during braking. Brake fluid is hygroscopic, which means it can absorb water, so it should always be kept in a sealed container when stored and a sealed system when installed in your vehicle. Since fluids cannot be compressed, they create a reaction within a sealed system according to a principal of science known as Pascal’s law (Force = Area x Pressure). By using this principle we can take a relatively small piston size inside the master cylinder and by depressing the pedal, exert physical force from the driver which will develop pressure inside the brake system. The pressure will be constant on all surfaces that it acts upon equally. It exerts this pressure through the brake system and when it contacts the surface area on the caliper or brake wheel cylinder, the pressure against those pistons amplifies the output force applied to the brakes themselves. The initial force of the driver is also assisted or amplified by a brake booster which can be vacuum, hydraulic, or electrically assisted. When the pedal is released, springs or seals allow the fluid pressure to decrease, which allows the brakes to release.

Think of blowing up a balloon: the air pressure pushes equally on the entire inside of the balloon’s surface. If you then push on the balloon, you compress it and force the balloon to squeeze out sideways. When you release the pressure, the balloon returns to its original shape. Air being compressed is a somewhat similar concept, yet air can be compressed while liquids cannot. Imagine what happens if you fill a water bottle completely to the top, put the lid back on tightly, and then step on the bottle really fast and hard. The bottle will resist until the force is great enough to pop the lid off or the bottle breaks.

Having the proper brake fluid type for your vehicle allows it to absorb the heat without boiling and push or apply adequate pressure to the brake pads or shoes to stop your vehicle. In the event of a brake system failure your pedal may go too low or even to the floor, requiring you to pump it several times to attempt to brake. Proper care of brake components and fluid will keep your brake system in top performance, allowing for safer stops. Make sure to have the fluid level and condition checked on a regular basis and have the fluid changed or flushed on a regular basis every couple of years, or better yet have this done when your brakes are replaced.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. How Does Brake Fluid Work?

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: More brake noise than there should be, low mileage

The brakes squeaking can be caused by the brakes overheating either from a caliper issue or glazed rotors and pads. When it comes to doing brake repairs, a brake job consisting of rotors and brake pads can only be part...

Q: Q: Master or slave cylinder?

Hi there. If you seen the slave cylinder move a little, then the piston on the slave cylinder could be stuck. Check all of the fluid and make sure that it is full on the clutch master cylinder. Have someone...

Q: Q: How do you check the power steering fluid?

Power steering fluid is vital for the system to work correctly. However, your car may or may not have a hydraulic system. If you have the 2.5-liter engine or the 3.0-liter engine, your system is completely electronic and does not...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...