Your brake system is a hydraulic system. As you step on your brakes a piston in the master cylinder compresses brake fluid. This brake fluid is forced through the brake lines to the caliper to act on the brake pads. If you have a leak in your brake system air can get in. Air in the brake system reduces the pressure that the brake system can generate. As you step on the brake pedal the brake fluid compresses the air in the brake lines instead of increasing the pressure of the brake fluid. By bleeding the brakes you can remove the air, moisture and any other contaminants in the hydraulic system. Also, Mercedes Benz recommends the brake fluid gets flushed at specific intervals. Seals in the brake system wear out and these particulates can accumulate in the master cylinder, calipers and ABS brake systems causing components to stick and possibly fail. In this tech article we will go over all the steps to bleed your brake system.
Mercedes Benz recommends you replace your brake fluid every 2 years.
Now there are a few ways you can bleed your brake system depending on the
level of equipment you have. The best way and fastest way to bleed the
brakes are pressure bleeders. These pressure bleeders are filled with brake
fluid. You add air to a bladder on the other side of the brake fluid
diaphragm and this pressurizes the brake fluid. You attach this pressurized
brake fluid, through adapters, to the brake master cylinder fluid reservoir.
Now pressurized brake fluid is being applied to the brake system of the car.
All you have to do is open the bleeder screw and old brake fluid will be
forced out. Keep the line open until you see clean brake fluid coming out of
the bleeder screw without any air bubbles in it. There are two types of
these pressure bleeders; one uses shop air to generate pressure and one has
a manual pump built into it. We have an air powered pressure bleeder and
that is what we are going to show you.
A second type of powered bleeding system is the vacuum type bleeder. Here you attach a vacuum pump to the bleeder screw on the caliper. There are two types of vacuum generating bleeder systems. One uses compressed shop air if you have a compressor the other has a manual pump that generates the vacuum. Make sure the reservoir is full and apply a vacuum to the bleeder screw then open the screw. The tool will draw the old brake fluid out and it will be replaced with the new fluid you put in the master cylinder reservoir.
Finally the last method requires a helper. The helper
will pump on the brake system and finally hold it down to generate the
necessary brake system pressure. While they are pushing the pedal to the
floor you open one of the bleeder screws. Fluid and air will come out and
the brake pedal will sink to the floor. When the brake pedal hits the floor
have them hold it there until you close the bleeder screw. Have your helper
release the brake pedal and pump the pedal up 2 to 3 times again. Open the
bleeder screw again and repeat this step at the same brake caliper several
times until the brake fluid runs clear and is free of air bubbles. Mercedes
Benz recommends you start at the right side rear wheel, followed by the left
side rear wheel, followed by the right side front wheel and finally the left
side front wheel. Make sure the brake fluid reservoir is topped off each
time you switch to bleed a different wheel.
Mercedes Benz recommends you exchange your brake fluid every two years.
In order to bleed the brakes you should lift and support your vehicle. It will be more difficult on the ground where you have to reach behind the wheels while you open and close the brake caliper bleeder screw. It is possible but makes the job more difficult.
See our tech article on jacking up and supporting your vehicle. You do not have to remove the wheels as we have done. We have removed the wheels for photographic purposes.
Make sure the brake fluid level is topped up before we start.
Attach the power bleeder attachment and make sure it is tight on the brake master cylinder reservoir so you do not have a mess on your hands.
We are using an air powered pressure bleeder. Squeeze the trigger and it applies the correct brake fluid pressure. Follow the instruction of your manufacturer on your pressure bleeder. Apply no more than 10psi of brake fluid pressure to the brake system.
Mercedes Benz recommends you start at the right rear wheel, followed by the left rear wheel, followed by the right front wheel and finally ending at the left front wheel, which is where we are now finishing the steps. Attach a 9mm line wrench to the bleeder screw. Also install a clear plastic hose to the nipple of the brake caliper bleed screw.
With pressurized brake fluid applied to the system open each bleed screw one at a time at each wheel until the brake fluid flows new brake fluid and there are no air bubbles in the system.