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:

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.

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.



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.

Tools Required

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.



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.



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. Refer to Master Cylinder Reservoir Filling .