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Pelican Technical Article:

Brake Bleeding

Nick Czerula

Time:

1 hour1 hr

Tab:

$30

Talent:

**

Tools:

11mm flared nut wrench, pressure bleeder

Applicable Models:

BMW X5 (2001-06)

Parts Required:

Brake fluid, brake cleaner

Hot Tip:

Bleed vehicle twice to ensure all air is removed from system

Performance Gain:

Good brake operation

Complementary Modification:

Replace worn brake parts

The brake pedal in your BMW X5 E53 is attached to a piston inside the brake master cylinder. When you step on your brake pedal the piston compresses the brake fluid behind it in the master cylinder. The brake fluid under pressure travels through 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 open up the brake hydraulic system (for example: to replace hydraulic components) you allow air to get into brake fluid. Bubbles of air are compressible (as opposed to the brake fluid itself which is not) and, when pressurized, compress. This gives the brake pedal a spongy feel and leads to poor braking. In addition, brake fluid is hygroscopic, which means that it absorbs water. The water in brake fluid can corrode metal components in the hydraulic system. Also, when the brake fluid becomes hot (for example: during heavy a bout of heavy braking), the water in the fluid can boil and form bubbles of steam, causing the same sort of mushy, spongy feel in the brake pedal as is caused by the presence of air bubbles in the brake fluid.

Removing air bubbles from the brake hydraulics after hydraulic component replacement is referred to as bleeding the brakes. Removing old brake fluid (full of impurities and hygroscopically absorbed water) and replacing it with fresh brake fluid is referred to as flushing the brake fluid. Bleeding and flushing are essentially the same procedure. Even if you have not opened the hydraulic system for component replacement, 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. The maximum pressure you want to run through the brake system using a pressure bleeder is 10 PSI. 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.

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 special tools but you will need a helper. Make sure to clean around the brake fluid reservoir 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. 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 that the right rear 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.

Install a box wrench on the right rear bleeder screw. Then install a hose to the brake bleeder screw nipple. This helps to keep your wheels clean during the process.

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 counterclockwise. 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. 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. When the fluid stops flowing or the pedal sinks all the way to the floor, close the bleeder screw. Look for air bubbles. When you no longer see bubbles move on to the next wheel. 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.

This is important: After each wheel check the fluid level in the brake fluid reservoir and refill it if necessary. If you don't do this and the reservoir empties out, you will pump additional air into the hydraulic system. Then you will have to start the whole process over again.

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 cleaner will evaporate into the air with time. Make sure the brake fluid reservoir is full and install the cap.

To begin, raise and support vehicle on jack stands. See our tech article on jacking up your vehicle.

The brake master cylinder is located below the wiper cowl trim (red arrow) on the left side of the vehicle.
Figure 1

The brake master cylinder is located below the wiper cowl trim (red arrow) on the left side of the vehicle.

Remove the rubber seal (red arrow) from the cowl.
Figure 2

Remove the rubber seal (red arrow) from the cowl. Lift it at one end and pull it up to remove.

Next, rotate the plastic retaining tabs (red arrows) 90° to release them.
Figure 3

Next, rotate the plastic retaining tabs (red arrows) 90 degrees to release them.

With all of the tabs released, lift the cowl trim up in the direction of the red arrow and remove from the cowl.
Figure 4

With all of the tabs released, lift the cowl trim up in the direction of the red arrow and remove from the cowl.

Make sure to clean around the brake fluid reservoir cap before removing it, as you do not want to get any dirt into the reservoir.
Figure 5

Make sure to clean around the brake fluid reservoir cap before removing it, as you do not want to get any dirt into the reservoir. Pull the wiring harness (red arrow) out of the side of the master cylinder. Remove fluid level sensor electrical connector by pressing locking tab (green arrow) and pulling off.

Remove the brake fluid reservoir cap (red arrow).
Figure 6

Remove the brake fluid reservoir cap (red arrow). Using a fluid extractor, remove all of the fluid from the reservoir. Then fill with fresh fluid.

It is very important that you keep the reservoir full during the brake bleeding procedure.
Figure 7

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. Then install the pressure bleeder adapter to the brake master cylinder (red arrow). Follow the instruction that came with your bleeder. The clutch master also uses the brake master cylinder reservoir via an attached line. Bleeding the clutch is similar to the brakes. Pressurize the brake system to a maximum of 10 psi.

Bleed the right rear caliper, followed by the left rear wheel, then the right front caliper and finally the left front brake caliper.
Figure 8

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 that the right rear brake line is the longest. Install a box wrench on the bleeder screw, then install a hose to the brake bleeder screw nipple (red arrow). This helps to keep your wheels clean during the process. Open the bleeder screw, allow the fluid the run out into a drain pan until no air bubbles are present and clean fluid is being expelled. Once the fluid is air-free, close the bleeder and repeat for the left rear wheel. 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.

Repeat these steps working your way around the vehicle (red arrow), right front wheel, then finally ending with the left front wheel .
Figure 9

Repeat these steps working your way around the vehicle (red arrow), right front wheel, then finally ending with the left front wheel. Be sure the brake fluid reservoir is full and install the cap.

Once the fluid is air-free, close the bleeder.
Figure 10

Once the fluid is air-free, close the bleeder. Check the fluid level (red arrow) 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.

If you are having trouble getting the air of out of the system, you may need to perform the bleeding functions using a BMW scan tool (red arrow).
Figure 11

If you are having trouble getting the air of out of the system, you may need to perform the bleeding functions using a BMW scan tool (red arrow). The bleeding functions cycles the ABS pump and valves to clear any air. Once you run the bleed function, try bleeding the system again, from the beginning of the procedure.

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Page last updated: Mon 12/5/2016 03:03:59 AM