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Pelican Technical Article:

Brake Bleeding

Kerry Jonsson

Time:

1 hour1 hr

Tab:

$10

Talent:

**

Tools:

10mm wrench

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Brake fluid

Hot Tip:

Put tie wrap around hose on bleeder screw to prevent a mess

Performance Gain:

Improved braking, remove old brake fluid

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.
Figure 1

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.
Figure 2

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.
Figure 3

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.
Figure 4

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.
Figure 5

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.

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Comments and Suggestions:
Mark Comments: Hello,
I usually do the brake pump technique with my wife's help. I recently read , not to let the brake pdeal go all the way to the floor and yo use a block of wood to limit this as it may damage the master cylinder. Is this true?

Also, should I cap the full reservoir during pumping for fluid flush, making sure it stay full of new fluid of course?
March 27, 2017
  Followup from the Pelican Staff: This is one of those extra careful instructions, truth be told I have done many flushes using the foot pump method all the way down without issues, it's that 1 in 500 that does have an issue which prompts us to advise you all not to push to the floor.

I usually cap the reservoir during this type of fluid flush YES. - Casey at Pelican Parts
 
NewShockerGuy Comments: According to the MB procedure for 2009 w211's you should pressurize the brake reservoir to 2bar 29psi
10psi as listed on here is not enough to push the air if there is any out.

They also recommend while doing the above that someone is in the car to actually push the brake pedal.
February 20, 2017
  Followup from the Pelican Staff: It says "IF the system was opened for repair" if not the 10 PSI is fine. Thanks for posting the MBZ info. It will help someone! - Casey at Pelican Parts  
Raj Comments: Hi Nick,
I have a 2006 E320 CDI with SBS brake system. Somewhere I have read that some precautions should be taken to avoid injury to yourself or to the system. Can you please post the bleeding system for SBS with the precautions included. Thanks.
October 30, 2016
  Followup from the Pelican Staff: We don't currently have that tech article. If we get a chance to perform the procedure, we will be sure to document it.


I would grab a repair manual. It will have the procedure, special tools and torque specs.


Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
PeteL Comments: Some MB forums say you should not completely empty the master cylinder reservoir to avoid getting air into the circuit - leave 1/4 inch in there.

But wouldn't that leave old fluid in the system?
October 27, 2016
  Followup from the Pelican Staff: If you push it all out. I prefer to suck it all out, refill then bleed. Air won;t enter unless you actuate the brakes when the reservoir is empty. - Nick at Pelican Parts  
PSH Comments: Hi, Can we do the same for mercedes with SBC, on the replay to Mine you say ABS, but from 2003 -2006 All W211 have SBC system, do you have any artical for brake bleeding this system, or does it have to bee only in the dealer?
June 22, 2016
  Followup from the Pelican Staff: For a normal bleed procedure, without introducing air into the module; this procedure should work for you vehicle. - Nick at Pelican Parts  
Mike Comments: I do not believe this technique is effective if you have the Sensotronic Brake Control system SBC. I have not been able to find a cost effective substitute to the dealer for this yet as you need a computer to activate the "brake bleeding" process. I'm open to ideas, but this is a very expensive piece of equipment to replace if you make a mistake e.g. - I am not a big fan of deactivating the system as a workaround.
November 10, 2014
  Followup from the Pelican Staff: The computer is only required if you introduced air at the ABS solenoids. If bleeding the brakes for the sake of a flush or caliper replacement, this method works fine.- Nick at Pelican Parts  

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Page last updated: Sun 5/28/2017 02:33:33 AM