Accepted Answer

Are the base brakes including the rear shoes adjusted up properly and have plenty of friction material? I would be temptedto acquire the correct master cylinder bleeding adaptor and bench bleed both front and rear ports again.

 

Master Cylinder Bench Bleeding

Bench bleed the master cylinder before installation on the vehicle. Bench bleeding removes air from the master cylinder. Bench bleeding reduces the time required in order to bleed the brake hydraulic system after installation.

1. Plug the outlet ports.
2. Mount the master cylinder in a vise with the front end slightly down.
3. Fill the master cylinder reservoir with clean brake fluid.
4. Stroke the primary piston about 25 mm (1 in) several times using a smooth round-end tool. The primary piston will not travel the full 25 mm (1 in) stroke as air bleeds from the master cylinder.
5. Reposition the master cylinder in the vise with the front end tilted slightly up.
6. Stroke the primary piston about 25 mm (1 in) several times again.
7. Level the master cylinder in the vise.
8. Loosen the plugs in the outlet ports one at a time.
9. Push the piston into the bore in order to force the air from the cylinder. Tighten the plug(s) before allowing the piston to return to its original position. This prevents air from being drawn back into the cylinder.
10. Fill the master cylinder reservoir with clean brake fluid.
11. Follow normal bleeding procedures after installing the master cylinder. Refer to Hydraulic Brake System Bleeding .
12. Hydraulic Brake System Bleeding

    If air has entered the hydraulic brake system, bleed the system. You may need to bleed the hydraulic brake system at all four wheels due to one of the following conditions:

    •	Air entered the system due to a low fluid level.

    •	The brake pipes have been disconnected at the master cylinder.

    •	The brake pipes have been disconnected at the combination valve.

    If a pipe is disconnected at one wheel, then only bleed that wheel.

    If the master cylinder has been removed, bleed the master cylinder before installing it on the vehicle. This will reduce the time required to bleed the system. Refer to Master Cylinder Bench Bleeding .

    Notice: Brake fluid will damage electrical connections and painted surfaces. Use shop cloths, suitable containers, and fender covers to prevent brake fluid from contacting these areas. Always re-seal and wipe off brake fluid containers to prevent spills.

    Manual Bleeding

    Tools Required

    J 28434 Wheel Cylinder Bleeder Wrench

    1. If the vehicle has a vacuum booster, apply the brakes several times with the ignition OFF. This relieves the vacuum reserve.
    2. Fill the master cylinder reservoir. Use Delco Supreme 11® Hydraulic Brake Fluid GM P/N 12377967, or equivalent DOT 3 motor vehicle brake fluid.

       Maintain the fluid level during bleeding.

    3. If the master cylinder has air in the bore, bleed the master cylinder using the following procedure:

       3.1.	Disconnect the forward brake pipe connector at the master cylinder. Refer to Master Cylinder Bench Bleeding .

       3.2.	Allow the brake fluid to flow from the connector port.

       3.3.	Connect the brake pipe connector. Do not tighten the brake pipe connector.

       3.4.	Slowly apply the brake pedal. Allow the air to bleed from the loose connector.

       3.5.	Tighten the connector before releasing the brake pedal.

       3.6.	Wait 15 seconds.

       3.7.	Repeat this sequence, including the 15-second wait, until you purge all the air from the master cylinder bore.

       3.8.	Repeat this procedure for the rear brake pipe after you purge all the air from the forward pipe connection.

    4. If you replaced the Brake Pressure Modulator Valve of the 4WAL system, or if you suspect that air is trapped inside, bleed the Brake Pressure Modulator Valve next. Refer to Antilock Brake System Automated Bleed Procedure .
    5. UsingJ 28434 , bleed each wheel cylinder in the following sequence:

       5.1.	Right rear wheel cylinder

       5.2.	Left rear wheel cylinder

       5.3.	Right front wheel caliper

       5.4.	Left front wheel caliper

    6. Attach a hose to the wheel cylinder/caliper bleeder valve.
       

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    7. Immerse the opposite end of the hose into a container partially filled with clean brake fluid.
    8. Slowly apply the brake pedal one time and hold.
    9. Loosen the bleeder valve in order to purge the air from the wheel cylinder/caliper.

       Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

    10. Tighten the bleeder valve.

        Tighten
        Tighten the bleeder valve to 13 N·m (110 lb in).

    11. Slowly release the brake pedal.
    12. Wait 15 seconds.
    13. Repeat this sequence, including the 15-second wait, until you purge all the air from the wheel cylinder or caliper.
    14. Repeat steps 6-12 at each wheel until you purge all the air from the brake system.
    15. Check the brake pedal for sponginess. Check the brake warning lamp for an indication of unbalanced pressure. Repeat the bleeding procedure in order to correct either of these conditions.

    Pressure Bleeding

    Tools Required

    •	J 29567 Brake Bleeder Adapter

    •	J 28434 Wheel Cylinder Bleeder Wrench

    Use a diaphragm-type pressure bleeder. The pressure bleeder must have a rubber diaphragm between the air supply and the brake fluid. This prevents air, moisture, oil and other contaminants from entering the brake hydraulic system.

    1. Fill the pressure tank at least 2/3 full of brake fluid.
    2. Charge the pressure bleeder to 140-170 kPa (20-25 psi).
    3. Bleed the pressure bleeder each time you add fluid.
       

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    4. Install the J 29567 Brake Bleeder Adapter to the master cylinder.
    5. If the Brake Pressure Modulator Valve of the 4WAL system is replaced, or if you suspect that air is trapped inside, bleed the Brake Pressure Modulator Valve first. Refer to Antilock Brake System Automated Bleed Procedure .
    6. Using J 28434 , bleed each wheel cylinder or caliper in the following sequence:

       6.1.	Right rear wheel cylinder

       6.2.	Left rear wheel cylinder

       6.3.	Right front wheel caliper

       6.4.	Left front wheel caliper

    7. Connect the hose from the bleeder to the adapter at the master cylinder.
    8. Open the tank valve.
    9. Attach a hose to the bleeder valve.
       

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    10. Immerse the opposite end of the hose into a container partially filled with clean brake fluid.
    11. Slowly open the bleeder valve at least 3/4 of a turn. Allow the fluid to flow until you see no air in the fluid.

        Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

    12. Tighten the wheel cylinder or caliper bleeder valve.

        Tighten
        Tighten the wheel cylinder or caliper bleeder valve to 13 N·m (110 lb in).

    13. Check the brake pedal for sponginess. Repeat the bleeding procedure if the brake pedal is spongy.
    14. Repeat steps 9-12 at every wheel.
    15. Disconnect the hose from the bleeder adapter.
    16. Remove the J 29567 Brake Bleeder Adapter.
    17. Fill the master cylinder to the proper level.
    18. Antilock Brake System Automated Bleed Procedure

        Two Person Bleed Procedure

        Important:

        •	Use the two-person bleed procedure under the following conditions:

        -	Installing a new Electro-Hydraulic Control Unit (EHCU) or new Brake Pressure Modulator Valve (BPMV).

        -	Air is trapped in the valve body

        •	Do not drive the vehicle until the brake pedal feels firm.

        •	Do not reuse brake fluid that is used during bleeding.

        •	Use the vacuum, the pressure and the gravity bleeding procedures only for base brake bleeding.

         

        1. Raise the vehicle in order to access the system bleed screws.
        2. Bleed the system at the right rear wheel first.
        3. Install a clear hose on the bleed screw.
        4. Immerse the opposite end of the hose into a container partially filled with clean DOT 3 brake fluid.
        5. Open the bleed screw 1/2 to one full turn.
        6. Slowly depress the brake pedal. While the pedal is depressed to its full extent, tighten the bleed screw.
        7. Release the brake pedal and wait 10-15 seconds for the master cylinder pistons to return to the home position.
        8. Repeat the previous steps for the remaining wheels. The brake fluid which is present at each bleed screw should be clean and free of air.
        9. This procedure may use more than a pint of fluid per wheel. Check the master cylinder fluid level every four to six strokes of the brake pedal in order to avoid running the system dry.
        10. Press the brake pedal firmly and run the Scan Tool Automated Bleed Procedure (with Gas) once, or run the Function Test (with Diesel) four times. Release the brake pedal between each test.
        11. Bleed all four wheels again using Steps 3-9. This will remove the remaining air from the brake system.
        12. Evaluate the feel of the brake pedal before attempting to drive the vehicle.
        13. Bleed the system as many times as necessary in order to obtain the appropriate feel of the pedal.

Expert:	Dan
Pos. Feedback:	99.0 %
Accepts:
Answered:	8/21/2008

Auto Technician

GM Mark of Excellence/ Service Guild Participant with 13 years experience, ASE Master Certified