Introduction: How to Do a Brake Fluid System Flush
Video tutorial on how to flush your brake system using a vacuum pump. Brake fluid should be changed at certain maintenance intervals, but it is something that gets overlooked. Maintenance intervals will most likely be dependant on your vehicle’s listed specifications, but as a general guideline it should be done at 40,000 miles/65,000km or every 3 years or under any major brake system repairs. There are some vehicles that have never had their fluid changed all their life, but this can jeopardize your safety as well as form premature wear on parts. Even though this is a closed system, moisture can come in contact with the fluid. This in turn can make parts internally rust or corrode, along with reducing the boiling point of the brake fluid which can cause brake fading under heavy usage.
- jack/axle stands
- line wrench or box end wrench
- socket set
- rubber gloves
- safety glasses
- drain pan
- new brake fluid
- brake cleaner
- vacuum pump kit
- wheel wrench
First determine which style of brake fluid your vehicle requires and how much fluid the system takes. Here I am working with a 1997 BMW 540i and it requires a DOT 4 brake fluid. A vacuum pump kit should have came with various types of hoses, attachments, along with a small reservoir in the kit. Install the correct hoses, along with the reservoir in the center. When working with brake fluid, DO NOT allow it to come in contact with the paint, either by dripping or even just the residue on your hands, as it can damage your vehicle’s paint.
Ensure that the master cylinder reservoir is clean so this reduces the risk of dirt entering the system. Start by removing the fluid from the master cylinder reservoir, insert the hose from the vacuum pump into the reservoir, pump the handle and it will suck out the fluid. Once the reservoir is about 3/4 full on the vacuum pump, empty it. Ensure that most of the fluid has been removed, then replace with the new fluid, and fill to the maximum line, then place the cap back on the reservoir.
Jack the vehicle up safety, apply a jack/axle stand, and remove the furtherest wheel which will be on the opposite corner. Located the bleeder screw, for brake callipers they are normally located towards the top on the rear, for drum brakes they are located through the backing plate on the top side. Use a line wrench, box-end wrench, or socket to loosen the bleeder screw, then tighten it back up. Using the closed end of the wrench, insert it onto the bleeder screw, install the rubber line from the vacuum pump, ensure it fits tightly. Pump the vacuum up to about 25 inches of mercury, break the bleeder screw, and the fluid will be sucked into the vacuum pump reservoir. Do not let the vacuum to go under 5 inches of mercury as we always want a negative pressure at the screw so there is no chance of air entering the system. When removing the fluid, it is very important to keep an eye on the fluid in the master cylinder reservoir. The fluid level MUST NOT go under the minimum line as we do risk introducing air into the system, so replenish brake fluid when needed. Once it's time to empty the vacuum pump, tighten the bleeder screw, remove the reservoir, and then continue the steps above again. When removing the old fluid, we are looking for clean fluid in the rubber line which will demonstrate that the old fluid has been remove from this location. Working from the furthest wheel, in order to remove all the old fluid from this location, it took about 6-7 ounces, but this amount will vary depending on your vehicle. Once you've reach clean brake fluid, tight the bleeder screw and continue the same procedure for the next furthest wheel. If you accidentally get fluid on the braking surface, it must be cleaned as this will cause issues. Slightly less fluid will need to be removed once you get closer to the master cylinder.
After all four wheels are done and you’ve kept a constant eye on the fluid level, check your brakes to ensure the brake pedal is firm, pump the pedal a few times and inspect for leaks just to be safe.