How to Change Brake Fluid

Learning how to change brake fluid can help extend the life of your brakes. Brake fluid can be compromised by moisture (which lowers its boiling point), air (which reduces stopping power) and debris (which can damage internal brake components).

Help Your Brakes By Replacing Brake Fluid

Although brake fluid only needs to be changed every 30,000 miles or so, neglecting this task can cause excessive wear on your car's brake components. The process of changing brake fluid is often referred to as "bleeding" the brakes. In order to keep air, debris and moisture out of brake lines, new brake fluid is put into the system as the old fluid is extracted. Here's how to change break fluid and limit costly repairs:

  • By the book. An owner's or service manual will help you to locate the bleeder valves on your car. Although most cars need to start with the brake farthest from the master cylinder, a service manual will tell you in what order the brakes need to be bled.
  • Going up. Chock the tires so the car won't slip off the jack. Loosen the lug nuts on the appropriate wheel. Jack the car up and remove the wheel. Lower the car onto a jack stand.
  • Start clean. First, locate the master brake cylinder reservoir in the engine compartment. The reservoir is typically located near the driver's seat. In cars made after about 1980, the brake fluid reservoir is made of plastic-older units may be made of metal. Clean the outside of the reservoir of any dirt, grease or loose debris. Open the brake fluid reservoir and remove as much brake fluid as possible using a siphon or large syringe-an old turkey baster is perfect for this task. Refill the master brake cylinder reservoir with new brake fluid.
  • Out with the old. Your goal at this point is to replace the old brake fluid in the brake lines with new fluid. As fluid is removed from the brakes, it is replaced by new fluid in the master cylinder reservoir. It is important to keep the reservoir topped off with fluid at all times to keep air from entering the system. A bleeder valve located on the brake caliper controls the fluid drain. Opening the bleeder valve allows brake fluid to flow from the brake line until new, clean fluid appears.
  • Extraction methods. There are several ways of extracting old brake fluid, including:
    • Gravity - Opening the bleeder valve and allowing fluid to drain until it is clear. This method is time consuming, but limits the chances that debris will be introduced into the brake system.
    • Pump and Drain - While the brake pedal is depressed (by a helper) the bleeder valve is opened. The pressure on the pedal forces brake fluid through the system. This method requires coordinated communication to avoid backpressure, which will introduce air into the system.
    • Vacuum - A special hand pump is attached to the bleeder valve and brake fluid is sucked through the brake lines. Unless properly sealed, vacuum systems can draw air into the pump line, making it hard to be certain air is removed from the system.
    • Pressure - A special pump is filled with brake fluid and attached to the master cylinder reservoir. With the bleeder valve open, fresh brake fluid is pumped through the system to flush the old fluid out. Although the pump can be expensive, this is the method preferred by professional mechanics.
  • Repeat until complete. The brake bleeding procedure must be completed on all four wheels to fully purge the system of old brake fluid.
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