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Pelican Technical Article:

BMW E39 Brake Bleeding

Kerry Jonsson

Time:

1.5 hours

Tab:

$25

Talent:

***

Tools:

17mm Socket (if removing tires), 11mm flare nut wrench, bleeder tool

Applicable Models:

BMW E39 5-Series (1997-03)

Parts Required:

Brake bleeder screw, brake fluid

Hot Tip:

Bleed entire brake system and change fluid in master cylinder reservoir. Use gloves, brake dust and brake cleaner are harmful

Performance Gain:

Great brake feel, brake flush recommended every two years

Complementary Modification:

Replace brake pads

When you step on your brake pedal you are compressing a piston in your brake master cylinder. This cylinder is full of brake fluid. The brake fluid that is now under pressure travels through your brake lines and is finally applied to your caliper. It's the calipers job to squeeze down on the brake pads against the rotor to slow down your car. If you have opened up the system to service it or you just want to flush out the old brake fluid you should bleed your brakes. When the system is open air gets in. The bleeding process bleeds the air out of the system. If you add new fluid to the master cylinder reservoir as you bleed the brakes the old fluid is forced out and the new fluid is drawn in. BMW recommends your flush out your brake system every two years.

There are a few ways to bleed brakes. There are pressure bleeders available that apply pressurized brake fluid to the master cylinder reservoir. All you have to do is open a bleeder valve. The new fluid from the pressure bleeder tool is forced into the master cylinder with air pressure. The old fluid is forced out the bleeder screw. Simply open the bleeder until you see cleaner brake fluid come out and then close the bleeder screw.

There are vacuum bleeders that work on the vacuum principle. There are two types. One is an air powered one that uses shop air pressure to generate a vacuum in the tool. This vacuum source is piped to the bleeder screw. With vacuum applied open the bleeder screw and vacuum will suck out the old fluid until the new fluid from the reservoir comes out then close the bleeder screw. There are manual tools that have you manually pump the tool to generate the vacuum. You will have to close the bleeder screw from time to time and pump on the tool to make vacuum then open the bleeder screw again.

The final method does not require any tools but you will need a helper. This is the procedure we are describing in this tech article. If you have the aforementioned tools follow the tool manufacturer's instructions that came with the tool. If you are using a helper follow these steps.

You do not have to lift and support the vehicle but to make the job easier you may want to raise and support the vehicle and remove the wheels to have clearer access to the bleed screws. Here we have the wheels removed for photographic purposes.

This photo illustrates the brake fluid reservoir under the hood on the left side back by the windshield.
Figure 1

This photo illustrates the brake fluid reservoir under the hood on the left side back by the windshield. Remove the reservoir cap. You will have to remove the cabin micro filter housing to access it.

Make sure to clean around the cap before removing it, as you do not want to get any dirt into the reservoir.
Figure 2

Make sure to clean around the cap before removing it, as you do not want to get any dirt into the reservoir. Fill the reservoir with new brake fluid. It is very important that you keep the reservoir full during the brake bleeding procedure. If it runs dry you will allow air to get drawn into the system through the master cylinder and you will have to start all over again. Check the brake fluid level after bleeding each caliper. The BMW recommended procedure is to bleed the right rear caliper, followed by the left rear wheel, then the right front caliper and finally the left front brake caliper. The reason is this brake line is the longest. The brake line starts at the master cylinder on the right side, moves across the body to the hydraulic assembly and then to the back of the car to the right rear caliper. The next longest line is the left rear, followed by the right front and the shortest line is the left front.

Set up your bleeder bottle on the brake bleeder screw.
Figure 3

Set up your bleeder bottle on the brake bleeder screw. Put the hose of the bleeder bottle (yellow arrow) on the bleed screw of the caliper. Put an 11mm wrench (green arrow) on the bleeder screw as well.

Have your helper step on the brake pedal all the way to the floor and all the way back three full times, then have them hold the pedal firmly to the floor.
Figure 4

Have your helper step on the brake pedal all the way to the floor and all the way back three full times, then have them hold the pedal firmly to the floor.

Open the bleeder screw on the right rear caliper by turning the wrench counter clockwise.
Figure 5

Open the bleeder screw on the right rear caliper by turning the wrench counter clockwise. If you opened the brake system for service you will probably get air at first. If you are flushing your brake system watch the flow of the brake fluid in the hose. It should rush out then slow down. Your helper will feel the pedal sink to the floor. Tell them to keep the pedal pushed to the floor. This will prevent air being let back into the caliper.

Close the bleeder screw by turning it clockwise.
Figure 6

Close the bleeder screw by turning it clockwise. (green arrow).

Have your helper pump the brake pedal again three times and hold it to the floor again.
Figure 7

Have your helper pump the brake pedal again three times and hold it to the floor again.

Open the bleeder screw again and have your helper continue to force the pedal to the floor.
Figure 8

Open the bleeder screw again and have your helper continue to force the pedal to the floor.

When the fluid stops flowing or the pedal sinks all the way to the floor close the bleeder screw.
Figure 9

When the fluid stops flowing or the pedal sinks all the way to the floor close the bleeder screw. (green arrow) Look at the bleeder bottle clear tubing (yellow arrow) for air bubbles suspended in the fluid. When you no longer see bubbles move on to the next wheels. Repeat this process. As you bleed out the air in the system your helper will notice the brake pedal getting harder to press and sink more to the floor as you open the valve. This is good. This means you are purging air from the brake hydraulic system. This may take several times to get all the air out. When small air bubbles no longer appear coming out of the caliper you can move on to the next caliper. After each wheel check the fluid level in the brake fluid reservoir and refill it if necessary. Properly tighten all bleeder screws and return any wiring stays and the rubber caps as well. Spray any brake fluid on the vehicle with brake cleaner and let air dry. Use brake cleaner in a well-ventilated area and let the components air dry. The brake clean will evaporate into the air with time. Make sure the brake fluid reservoir is full and install the cap.

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Comments and Suggestions:
Rich Comments: Nick - one last question. Using the old fashioned two-person bleeding method, with the engine running and significant pressure on the brake pedal, I noted what might be considered "marginal" to "low" pressure at the master cylinder's brake lines. In other words, there was no "burst" of pressure that I might might have expected with booster engaged; it was slightly more than "low" pressure. I'm not sure how to gauge the pressure level at the master and I am inclined to replace the master in hopes that the DSC unit is good. Any advice on what is "good" pressure at the master?? Also, on hard braking, I noted that only the LF wheel locks up and immediately thereafter I hear the DSC pump engage. Thoughts? Thanks again!
September 11, 2016
  Followup from the Pelican Staff: Could be up to 1200 psi for a wheel, 3000 for two out of the master. BMW doesn't publish specs. - Nick at Pelican Parts  
Rich Comments: Thanks, Nick! Yes, good suggestion . . . should have thought of it myself. But's that's why it's great to have you guys in my corner when needed!
September 7, 2016
  Followup from the Pelican Staff: No problem. I have dealt with this issue many times. More often than not, I find a faulty DSC unit. Hopefully you don't. ;)- Nick at Pelican Parts  
Rich Comments: My problem is that unfortunately, I don't exactly know "where" the air in my system is. I have a spongy pedal and when I try to bleed the system with a pressure bleeder I get very little - almost nothing coming through the bleeder valves at each wheel. Although it's not bypassing, by default, I'm thinkin' master cylinder. Not sure why else I'd have a spongy pedal and be getting very little pressure at the wheels. Any thoughts?
September 2, 2016
  Followup from the Pelican Staff: If you are getting very little fluid flow, I would check each connection starting at the master. Hold pedal, crack master lines, is there good flow? The move to lines at DSC unit, and so on. - Nick at Pelican Parts  
Rich Comments: Okay, thanks. That would mean that if I replace the master cylinder I would need the scan tool in order to bleed the system?
September 2, 2016
  Followup from the Pelican Staff: No, not if you didn't introduce air into the DSC system. Which you would not if just the master was removed. - Nick at Pelican Parts  
Rich Comments: Hi guys - thanks for always being helpful!

Is this the same process for bleeding the brakes on an E39 with Dynamic Skid Control DSC? Can I just a pressure bleeder if I have DSC? I thought that the ABS pump needs to be activated using a computer in order to bleed the brakes - any thoughts? Can I activate the pump without a computer hook-up? Is it even necessary?

Thanks!
Richard
September 1, 2016
  Followup from the Pelican Staff: If you did not introduce air into the pump or DSC unit, you will not need a scan tool to bleed it. - Nick at Pelican Parts  

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Page last updated: Sat 12/3/2016 02:05:42 AM