Q: What causes brake fluid leaks?

asked by on

What causes brake fluid leaks?

There are many factors that can lead to brake fluid leaks.

Let’s begin at the start of the system, with the master cylinder. This is a sealed unit with a reservoir to hold the brake fluid needed to operate the system. It may include a sensor that will illuminate a light to indicate a low level. The actual operational part of the master cylinder contains internal pistons with seals to build the pressure needed to squeeze the brake pads or shoes to stop your car. The brake booster rod pushes on these pistons, which have an external rear seal to keep the fluid trapped inside the cylinder. When the brake pedal is depressed, the pistons push the fluid and transfer the pressure through the brake system. Over time these seals can become worn and leak either internally or externally. A sign of an external leak is an area of missing or peeling paint on the brake booster just below the rear of the master cylinder. If the brake pad wear is excessive, it is possible for the caliper pistons to be overextended in their bores and pop out past the seal, causing fluid to leak past the piston. Flexible rubber brake lines can dry, rot, and crack or be damaged from abuse, road debris, or an accident. Metal brake lines can rust out, especially those subject to severe conditions where excessive salt is used in winter weather conditions. If the vehicle is near a salt water source, it can have the same effect on the lines over time. The seals in wheel cylinders will also wear over time and can leak fluid out onto the brake shoes. Even a loose brake bleeder screw can cause a leak.

Have your vehicle checked if you notice problems like a low brake pedal or a pedal that sinks down as you sit at a light with pressure applied to the brake pedal. No problem with your vehicle should be ignored, but certainly anything to do with the brakes, tires, steering, or fuel system leaks should be addressed as soon as you feel them occur. As with all concerns, regular maintenance checks will help to keep potential problems in check.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. What causes brake fluid leaks?

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: How do I check the brake fluid?

Your car’s brakes are the most important safety system onboard. They’re hydraulic, which means they require fluid in order to operate. When you press the brake pedal, fluid is sent from the master cylinder through the brake lines to the...

Q: What kind of modification/performance can I do to my car?

Hello - the best way to keep your Altima running like new is "attentive maintenance". Keep fluids (oil, transmission fluid, coolant) topped off and changed at recommended intervals. If your timing chain and associated components (tensioner, idler, chain guides, etc.)...

Q: Sluggish shifting

Oil leaks, unfortunately, will only get worse over time. So identifying the type and source of the leak will be vital to the overall health of the vehicle. Some possibilities on the engine would be the valve cover area, the...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
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...