How to Check Your Car’s Brake Fluid Levels

Brake fluid is a type of hydraulic fluid used in hydraulic brake and hydraulic clutch applications in vehicles. It is used to transfer force into pressure, and to amplify braking force. Simply stated, when you apply your foot to the brake pedal, brake fluid transfers this force into pressure to the front and rear brakes and stops the vehicle. It works because liquids are incompressible.

Brake fluids must have certain characteristics and meet certain quality standards for the braking system to work properly. Brake fluid is subjected to very high temperatures, especially in the wheel cylinders of drum brakes and disk brake callipers. It must have a high boiling point to avoid vaporizing within the lines. Vaporization is a problem because vapour is highly compressible relative to liquid, and therefore negates the hydraulic transfer of braking force which will result in the brakes failing to stop the car.

Brake fluid is crucial to the safe operation of your vehicle. Have an ASE certified technician inspect your brake fluid level and test the condition at least annually. Check your owner’s manual for the recommended brake fluid replacement schedule and brake fluid type. Remember, brake fluid is what is between your brake pedal and the brakes at all four wheels. Make brake fluid a part of your regular maintenance routine, and replace the brake fluid when necessary to keep you and your passengers safe.

How to Check Your Brake Fluid

  • Locate brake master cylinder reservoir. It is usually mounted on or near firewall at rear of engine compartment, almost directly in front of where the brake pedal is mounted on other side of bulkhead. Consult vehicle’s owner’s manual if you’re having trouble identifying it.
  • Check fluid level.
  • Newer vehicles: Most newer vehicles have a translucent reservoir with a clearly marked “full” line. If your vehicle has this style reservoir, you can check the fluid level without removing the screw-off cap.
  • Older vehicles: Most older (early 1980s and older) vehicles have a metal reservoir with a top held on by a spring-loaded clamp. Wipe the exterior of the top clean to help prevent any debris from entering brake fluid. You’ll need to pry the clamp to one side, then lift off the top to inspect the level. The “full” line should be clearly marked.
  • If level is low, add brake fluid to “full” line.
  • IMPORTANT: A drop in brake fluid typically indicates that your brake pads have worn to the point of needing maintenance. Be sure to have your brakes checked by a professional.
  • CAUTION: DO NOT USE BRAKE FLUID OTHER THAN THE SPECIFIC TYPE RECOMMENDED FOR YOUR VEHICLE. Do not overfill. If your vehicle has a dual-chamber reservoir, fill both chambers to “full” line. If reservoir is extremely low or empty, it may not be safe to drive your vehicle. Consult an ASE-certified brake technician immediately.
  • Replace cap/top. You’re done!
  • WARNING: BRAKE FLUID MAY BE EXTREMELY TOXIC. WASH HANDS THOROUGHLY AFTER HANDLING. DO NOT GET IN EYES. DO NOT SPILL ON PAINT.

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