The hydraulic brake system must be bled whenever a fluid line has been disconnected because air gets into the system. A leak in the system may sometimes be indicated by a spongy brake pedal. Air trapped in the system is compressible and does not permit the pressure applied to the brake pedal to be transmitted solidly through the brakes. The system must be absolutely free from air at all times. If the master cylinder has been overhauled or a new cylinder has been installed, bleed the cylinder on a bench before installation. When bleeding brakes, bleed at the wheel most distant from the master cylinder first, the next most distant second, and so on. During the bleeding operation the master cylinder must be kept at least 3 / 4 full of brake fluid.
The ABS bleeding procedure is different from the conventional method. It consists of the following three steps:
Step 1: Conventional manual brake bleed.
Step 2: Bleeding the system using the DRB scan tool.
Step 3: An additional conventional manual brake bleed.
The recommended ABS bleeding procedure is as follows:
- To bleed the brakes, first carefully clean all dirt from around the master cylinder filler cap. Remove the filler cap and fill the master cylinder with DOT 3 brake fluid to the lower edge of the filler neck.
- Bleed the master cylinder first. Have a helper operate the brake pedal while bleeding each master cylinder fluid outlet line. Do not allow the master cylinder to to run out of fluid,as this will allow additional air to be drawn into the cylinder.
Bleed the brake system in the following sequence:
- Master cylinder
- HCU valve body (at fluid lines)
- Right rear wheel
- Left rear wheel
- Right front wheel
- Left front wheel
- Clean off the bleeder connections at all four wheel cylinders. Attach the bleeder hose to the right rear wheel cylinder bleeder screw and place the end of the tube in a glass jar, submerged in brake fluid.
- Open the bleeder valve 1 / 2 - 3 / 4 of a turn.
- Have an assistant depress the brake pedal slowly and allow it to return. Continue this pumping action to force any air out of the system. When bubbles cease to appear at the end of the bleeder hose, close the bleeder valve and remove the hose.
- Check the level of fluid in the master cylinder reservoir and replenish as necessary.
- After the bleeding operation at each wheel cylinder has been completed, fill the master cylinder reservoir and replace the filler plug.
Do not reuse the fluid which has been removed from the lines through the bleeding process because it contains air bubbles and dirt.
Perform the "Bleed Brake'' procedure with the DRB II scan tool. This procedure is described in the DRB II software information and diagnostic guide.
- Attach the DRB II scan tool to the diagnostic connector.
- Run the Bleed Brake procedure as described in the DRB II tester guide.
- Repeat the conventional bleeding procedure as previously outlined.
- Fill the master cylinder reservoir to the proper level.
- Check the brake operation.