Bleeding Brakes: A How-To Guide to Bleeding Brake Fluid

February 22, 2012

Bleeding brakes is an easy 5-step process that maintains your brake pedal's responsiveness and keeps braking distance from getting dangerously long.

Brake Servicing

Bleeding brakes is an important maintenance operation for any vehicle. The brake system is a hydraulic circuit that uses the driver's pedal input to create pressure in a series of lines. These lines direct pressure to the braking systems in each of the four wheels. This generates friction on the rotating wheel to slow the car. Brake systems wear out over time, and must be maintained effectively in order to provide maximum stopping power and insure driver and passenger safety.

Why Bleeding Is Necessary
Despite brake fluid's unique chemical properties, the fluid can break down over time, leading to a spongy-feeling pedal and an increase in the distance required to stop. Additionally, when replacing brake components or making any changes to the braking system air can be introduced into the brake lines. Special consideration must be taken to remove this air from the lines. Air is very compressible and will simply give under the intense pressure, giving the pedal a very spongy feel and increasing stopping distances dramatically.

How to Bleed Your Brakes
Bleeding a vehicle's brakes is a simple operation. With the help of a friend, you can easily do it yourself. First, you must have access to the brake caliper (for disc brakes) or slave cylinder (for drum brakes.) It may be necessary to remove the wheels to access these components. Locate the brake bleeder screw, usually a small metal nipple with a hexagonal base. Once you have located the bleeder screw, have your friend sit in the car. Follow these simple steps:

  • Make sure the master cylinder is full of fluid at all times
  • Pump the brake pedal two to three times and hold it
  • Turn the bleeder screw with a wrench until fluid streams out, inspecting for air bubbles
  • As the fluid escapes, the pedal will push to the floor. This is normal. Hold the pedal down
  • Once the fluid flow slows, close the bleeder screw

Repeat this process for each wheel until the fluid looks clean and free of air. Gently tapping on the brake components can help free air bubbles, and pushing a clear tube over the brake bleeder can help inspect fluid for air. Once you have finished bleeding, pump the brake pedal until it is firm and verify that the pedal feels appropriate. Remember, power brakes will not operate with the engine off, so the firmer the pedal the better.

Gravity Bleeding
An alternate method for bleeding the brakes is gravity bleeding. By simply opening the bleeder screws on all wheels, topping off the fluid and allowing the vehicle to sit for several hours, air can be removed from the system. This method works best on new brake systems that have no fluid in them, as it does not force old fluid from the lines.

Take the car for a short test drive to verify proper operation. Make sure to keep brake fluid off of painted surfaces, as it can cause damage to paint and plastics. Contact your local auto parts store for proper disposal of brake fluid.