Why is my car leaking brake fluid?

A brake job
Brake Image Gallery A puddle of brake fluid during service is OK -- but brake fluid beneath your vehicle any other time typically signals a leak. See more brake pictures.
Bryan Reese/iStockphoto

Do you suspect that your vehicle may have a leaky brake system? Is your brake fluid level just a little bit low? Well, one explanation for the low fluid level may be relatively simple: If your vehicle has worn brake pads or brake shoes, the fluid level in your brake fluid reservoir will be low. But let's say you have relatively new brake pads and you recently topped-off your brake reservoir only to notice a few days later that the fluid level has dropped noticeably. If that's the case, it's a good bet you have a leak somewhere in your brake system -- which means that you likely have bigger brake issues than something as simple as worn brake pads.

Your braking system is comprised of series of rubber and steel hoses, check valves, pistons and cylinders. They're all joined together, and work in concert to slow and stop your vehicle. It may help you to understand it all a little better if you imagine your brake system as a cardiovascular system, pumping blood to several different areas of the body. The vehicle's master cylinder acts as the heart and pumps brake fluid through brake lines to the extremities, in this case, the calipers and drums. This is where a lot of brake problems originate. At all four corners of your vehicle, brake lines -- with fittings that serve to connect the master cylinder to the different parts of the brake system that actually slow or stop your wheels -- quite simply, can leak. In fact, every part within the braking system that connects to another part has the potential to become yet another leak. Parts can become worn out or punctured or even pulled apart by road debris. Whatever the situation, if you have a brake fluid leak, you need to find and repair it as soon as possible.


To properly diagnose a brake leak, you must first locate the leaking point. The best way to do this is by parking your vehicle on a level surface for a couple of hours, then observing the position of the brake fluid that has accumulated beneath the vehicle. This will give you an idea as to which fitting may be the culprit. If you find that the puddle of brake fluid is beneath the rear of the engine -- not near one of the wheels -- you may have a leak somewhere in (or near) the master cylinder.

Bleeder bolts, sometimes called bleeder valves, are located on the brake calipers and are designed to allow brake fluid to flow out of the system. If you've recently had some brake work done on your vehicle, it may be that one of your bleeder valves was inadvertently left a little loose. If that's the case, it's a simple matter of tightening the valve to stop the fluid flow. 

­Perhaps you have a brake problem that includes a mushy, or soft, brake pedal. If you experience a brake pedal that goes straight to the floor with little or no resistance, you can quickly pump the pedal to build pressure. If you are unable to build pressure after several quick pumps, you may have a serious leak. It's possible that one of your vehicle's brake lines has been punctured or one of the fittings has failed. Both of these are easily fixed, but you must address them immediately -- your safety and the safety of other drivers depends on it.

Remember, brake fluid is essential for the brake system to operate properly. Leaks in the system release fluid, causing reduced (or even complete loss of) brake pressure. If you don't address the problem, your vehicle will eventually run out of brake fluid; however, chances are you won't get to that point, as the brakes won't continue to work after the fluid level drops beyond a certain level.




Lots More Information

Related HowStuffWorks Articles

More Great Links

More Great Links


  • Allen, Mike. "A Primer on Brake Fluids: DOT, DOT, Who's Got the DOT?"Popular Mechanics. April 2007. (Nov. 2, 2008) http://www.popularmechanics.com/automotive/how_to/4213450.html
  • Allen, Mike. "How to Bleed Your Brakes: Saturday Mechanic." Popular Mechanics.April 2007. (Nov. 2, 2008) http://www.popularmechanics.com/automotive/how_to/4213448.html
  • Ofria, Charles. "Automobile Brakes - A Short Course on How They Work." The Family Car Web Magazine. (Nov. 2, 2008) http://www.familycar.com/brakes.htm