Mercedes-Benz Cars 2000-05

Bleeding the Brake System

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When any part of the hydraulic system has been disconnected for repair or replacement, air may get into the lines and cause spongy pedal action (because air can be compressed and brake fluid cannot). To correct this condition, it is necessary to bleed the hydraulic system so to be sure all air is purged.

When bleeding the brake system, bleed one brake cylinder at a time, beginning at the cylinder with the longest hydraulic line (farthest from the master cylinder) first. The sequence for calipers with single bleeder screws is: right rear, left rear, right front then left front. For calipers with 2 bleeder screws, follow the illustration (note the difference in sequence for right and left hand drive vehicles). ALWAYS keep the master cylinder reservoir filled with brake fluid during the bleeding operation. Never use brake fluid that has been drained from the hydraulic system, no matter how clean it is.

The primary and secondary hydraulic brake systems are separate and are bled independently. During the bleeding operation, do not allow the reservoir to run dry. Keep the master cylinder reservoir filled with brake fluid.

  1. Clean all dirt from around the master cylinder fill cap, remove the cap and fill the master cylinder with brake fluid until the level is within 1 / 4 in. (6mm) of the top edge of the reservoir.
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  3. Clean the bleeder screws at all 4 wheels. The bleeder screws are located on the top of the brake calipers.
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  5. Attach a length of rubber hose over the bleeder screw and place the other end of the hose in a glass jar, submerged in brake fluid.
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  7. Open the bleeder screw 1 / 2 - 3 / 4 turn. Have an assistant slowly depress the brake pedal..
    CAUTION
    Brake fluid contains polyglycol ethers and polyglycols. Avoid contact with the eyes and wash your hands thoroughly after handling brake fluid. If you do get brake fluid in your eyes, flush your eyes with clean, running water for 15 minutes. If eye irritation persists, or if you have taken brake fluid internally, IMMEDIATELY seek medical assistance.

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  9. Close the bleeder screw and tell your assistant to allow the brake pedal to return slowly. Continue this process to purge all air from the system.
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  11. When bubbles cease to appear at the end of the bleeder hose, close the bleeder screw and remove the hose. Tighten the bleeder screw until just snug.
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  13. Check the master cylinder fluid level and add fluid accordingly. Do this after bleeding each wheel.
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  15. Repeat the bleeding operation at the remaining 3 wheels.
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  17. Fill the master cylinder reservoir to the proper level.
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  19. After the bleeding procedure, make sure you have a hard pedal that does not sink. Perform a test drive and engage the ABS system at least once. Be sure to do this safely, for example in an empty parking lot. Make sure the pedal remains hard after the ABS engagement. If not, repeat the bleeding procedure.

    Click image to see an enlarged view

    Fig. Bleeding sequence for calipers with 2 bleeder screws

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