Envoy 2WD V6-4.3L VIN W (1998)
Brake Bleeding: Service and Repair
Hydraulic Brake System 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.
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:
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Air entered the system due to a low fluid level.
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The brake pipes have been disconnected at the master cylinder.
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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 in order to reduce the time required to bleed the
system.
If the Brake Pressure Modulator Valve (BPMV) has been replaced or has air trapped it, refer to "Brake Pressure Modulator Valve Replacement" in
Antilock Brake System.
MANUAL BLEEDING
Tools Required
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J28434 Wheel Cylinder Bleeder Wrench
1. Apply the brakes several times with the ignition OFF in order to relieve the brake vacuum reserve.
2. Fill the master cylinder reservoirs with DOT 3 motor vehicle brake fluid.
3. Maintain the fluid level during bleeding.
4. If the master cylinder has air in the bore, bleed the master cylinder using the following procedure:
4.1. Disconnect the forward brake pipe connector at the master cylinder.
4.2. Allow the brake fluid to flow from the connector port.
4.3. Connect the brake pipe connector. Do not tighten the brake pipe connector.
4.4. Slowly apply the brake pedal and allow the air to bleed from the loose connector.
4.5. Tighten the connector before releasing the brake pedal.
4.6. Wait 15 seconds.
4.7. Repeat this sequence, including the 15 second wait, until all air is purged from the master cylinder bore.
4.8. Repeat this procedure for the rear brake pipe after you purge all the air from the forward pipe connection.
5. If the brake pressure modulator valve of the antilock brake system is replaced or if you suspect that air is trapped inside, bleed the brake pressure
modulator valve next. Refer to Brake Pressure Modulator Valve Replacement in Antilock Brake System.
6. Bleed each wheel cylinder 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. Attach J 28434 on the wheel cylinder or caliper bleeder valve.
8. Immerse the opposite end of the hose into a container partially filled with clean brake fluid.
9. Slowly apply the brake pedal one time and hold.
10. Loosen the bleeder valve in order to purge the air from the wheel cylinder or caliper.
11. Tighten the bleeder valve and slowly release the brake pedal.
12. Wait 15 seconds.
NOTICE: Refer to Fastener Notice in Service Precautions.
13. Repeat this sequence, including the 15-second wait, until all air is purged from the wheel cylinder or caliper.
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Tighten the bleeder valve to 7 Nm (62 inch lbs.).
14. Repeat steps 7 through 13 at each wheel until the brake system is bled.
15. Check the brake pedal for sponginess, and 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
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.
Tools Required
