Replacing Brake Fluid

Adding vs. Changing Brake Fluid

Adding brake fluid is usually not part of routine vehicle maintenance. Low brake fluid typically means that your brake pads are low and soon need to be changed. If you notice a sudden drop in the brake fluid level, it could indicate a problem with your brake system, or that you simply need to change your brakes.

Have a professional check your brakes if you are unsure. If you are sure that your brake pads are in serviceable condition and your brake fluid is below the add line, only then should you add fluid.

Symptoms of Brake Problems

Some braking problems have to do with the brake fluid. If your brakes have developed a "mushy" feel, or if they need to be pumped, then, rarely, air may have entered the line. Check the brake fluid level; if the reservoir is empty, then bleeding the brake lines to remove the air may improve the condition. However, if the reservoir still holds brake fluid, have the brakes checked as soon as possible.

Brake Fluid Facts

Keep these general facts in mind while handling brake fluid:

  • Never use DOT 5 brake fluid in a vehicle designed for DOT 3 or DOT 4 fluids.
    It is ok to use DOT 4 fluid in a vehicle that requires DOT 3, but not vice-versa.
  • NEVER substitute any other fluid for brake fluid.
  • Wash your hands immediately after coming in contact with brake fluid. It eats paint, so imagine what it'll do to skin.
  • Properly discard brake fluid that's been unsealed for more than one year. Check with your city for recycling days or centers.

How to Check and Add Brake Fluid

  • Determine the location of the brake fluid reservoir.
  • Look inside the reservoir to determine the current fluid level. If it's at the "full" mark, close the reservoir and mark the date of the inspection in your maintenance log.
  • If the fluid level is below the "add" line, have your disc brakes checked. As disc brakes wear down, the fluid is displaced into the brake calipers. Most brake fluid reservoirs are designed so you should not have to add or "top off" the fluid. If the fluid looks dark, it is time to have it changed.

Bleeding the Brake Lines to Remove Air

Usually, two people are required to bleed a brake line; one to depress the brake pedal and one to drain the fluid into a container. These directions are the basic procedure for bleeding a brake line. Consult your service manual before you begin to bleed your own lines; this WILL NOT work for newer cars.

Have the following items handy:

  • A section of plastic, vinyl or rubber tubing long enough to reach from the brake caliper to the clear plastic container.
  • A wrench to open and close the bleeder valve.
  • A clear plastic container containing at least one inch of clean brake fluid, or enough to submerge the plastic tubing. Clear plastic is important so you can see the air bubbles as they exit the brake line.

Here are the basic instructions for the process:

  • Open the reservoir and add brake fluid up to the full line.
  • Replace the cap on the master cylinder reservoir before you begin bleeding the line. Never remove the reservoir cap while the brake pedal is depressed.
  • Starting with the wheel rear wheels, locate the brake cylinder or caliper and find the bleed valve on the back side. It will look line a bolt with a nipple on it and may have a rubber cap that you will have to remove.
  • Place one end of the clear tube into the clear container to which you have added approximately one inch of brake fluid. Be sure to do this step before you connect the other end of the tube to the bleed valve.
  • With the tube end in the container of brake fluid, connect the other end of the tube to the bleed valve.
  • Use a wrench to loosen the valve on the brake caliper just slightly. Do not allow the brake fluid to begin to flow; just loosen the valve enough to make it easy to release when you are ready to bleed the line.
  • Now, have the person inside the vehicle pump the brake pedal a few times to build up pressure in the line, and then have them hold the brake pedal down firmly, without further pumping.
  • While the brake pedal is held in place, loosen the bleed valve enough to allow a small amount of brake fluid to flow out of the brake line and into your container.
  • Watch for the air bubbles to exit the tube placed in the clear plastic container with the brake fluid.
  • The person inside the vehicle should only allow the pedal to travel about 2/3rds of the way to the floor. Allowing the pedal to reach the floor may damage a master cylinder. Once the pedal reaches this position, the person inside should signals you with an "OK" so you know to tighten the bleeder screw. After the screw is tightened, signal the person inside with an "OK" so he may release the pedal.
  • Repeat this action of pumping the brakes and bleeding the fluid until there are no more bubbles remaining in the line. It is very important to remember to periodically check the fluid level in the reservoir, and always replace the cap before actuating the brake pedal.
  • Repeat the process above for the three remaining brake lines. Be sure your helper pumps and holds the brake pedal each time.
  • Once all four brake lines have been bled, fill the brake fluid reservoir to the "full" line, then close the cap,
    Thoroughly rinse any spilled brake fluid spilled in the engine compartment off with water.
  • If you are in any doubt about the condition of your braking system,make an appointment for a brake inspection as soon as possible.

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