Every two to three years, you need a brake fluid flush done on your vehicle. Brake fluid is hygroscopic, which means it pulls in water right out of the air. Old brake fluid also has some wear particles in it that combine with the water to corrode the inside of your brake system. The factory has taken the brake fluid change out of the recommended major services on the pretext that the fluid needs to be changed based on a time interval instead of at distinct mileage intervals. At Karmakanix, each technician has an instrument to measure the percentage of water accumulated, and when it reaches 3%, the brake fluid should be changed. Karmakanix uses a Pentosin Synthetic DOT 4 brake fluid that has a 5 year service life. It absorbs water slower and boils at a higher temperature than regular fluid.
Most modern systems require a pressurized brake bleeder to do a brake fluid flush. Many modern ABS systems also require a computer and a technician trained in the proper procedures. The technician needs to log into the vehicle’s ABS computer and open the correct valves so the brake fluid can circulate properly. Any VW or Audi from this century with a manual transmission has a hydraulic clutch that shares the same fluid. Getting to that bleeder can be troublesome. Some mechanics either don’t know about the clutch hydraulics or conveniently just skip it. And clutch hydraulic failure is more common than brake hydraulic failure. Most hydraulic clutch slave cylinders are inside the front of the transmission. Failing to change all of the brake fluid can cost you a clutch job.
Quick Clue: If you ever need to add brake fluid, make sure the bottle is not old and open. Brake fluid pulls water out of the air, and you can’t tell how contaminated it might be by looking at it.