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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12741
Experience:  Have owned a repair shop for 25 yrs.
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1998 Chevy: ton 4x4 with abs brakes

Customer Question

I have a 1998 Chevy 1/2 ton 4x4 with abs brakes. How do I bleed air out of system?
Submitted: 4 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 4 years ago.

hi

this may help..these anti-lock systems can be hatefull sometimes...also make sure you have the rear shoes ajusted all the way out against the hubs

thanks

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 inch) several times using a smooth round-end tool. The primary piston will not travel the full 25 mm (1 inch) 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 inch) 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. Hydraulic Brake System Bleeding.
ABS Bleed Procedure

Important:

  • Use the two-person bleed procedure under the following conditions:
  • Installing a new Electro-Hydraulic Control Unit (ECU) 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.

TWO PERSON PROCEDURE

  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 Automatic Bleed Procedure. 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.
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.

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, 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.
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.
  1. 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.
  2. Using J28434, 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
  1. Attach a hose to the wheel cylinder/caliper bleeder valve.
  2. Immerse the opposite end of the hose into a container partially filled with clean brake fluid.
  3. Slowly apply the brake pedal one time and hold.
  4. Loosen the bleeder valve in order to purge the air from the wheel cylinder/caliper.
  5. Tighten:the bleeder valve.
    • Tighten the bleeder valve to 13 Nm (110 inch lbs.) .

NOTICE: Refer to Fastener Notice in Service Precautions.

  1. Slowly release the brake pedal.
  2. Wait 15 seconds.
  3. Repeat this sequence, including the 15-second wait, until you purge all the air from the wheel cylinder or caliper.
  4. Repeat steps 6-12 at each wheel until you purge all the air from the brake system.
  5. 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. Bleed the bleeder each time you add fluid.
  3. Charge the bleeder to 140-170 kPa (20-25 psi).
  4. Install the J29567 Brake Bleeder Adapter.
  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.
  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
  1. Connect the hose from the bleeder to the adapter at the master cylinder.
  2. Open the tank valve.
  3. Attach a hose to the bleeder valve.

 



 

  1. Immerse the opposite end of the hose into a container partially filled with clean brake fluid.
  2. 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.
    • Tighten the wheel cylinder or caliper bleeder valve to 13 Nm (110 inch lbs.) .

NOTICE: Refer to Fastener Notice in Service Precautions. Check the brake pedal for sponginess. Repeat the bleeding procedure if the brake pedal is spongy.

  1. Repeat steps 9-12 at every wheel.
  2. Disconnect the hose from the bleeder adapter.
  3. Remove the J 29567 Brake Bleeder Adapter.
  4. Fill the master cylinder to the proper level.
Leading /Trailing Drum Brakes

A manual adjustment of the rear drum brakes is required after replacing the rear linings.

  1. Remove the lanced area in the backing plate.
  2. Turn the adjusting screw until the wheel can just be turned by hand.
  3. The brake drag should be equal at both wheels.
  4. Back off the adjusting screw 20 notches. Brakes should have no drag after the adjusting screw is backed off about 10 notches. If a heavy drag is still present, refer to Park Brake Cable Service/Adjustment (Adjustment).
  5. Install an adjusting hole cover in the backing plate.
  6. Check the parking brake adjustment.

REMOVAL PROCEDURE
GM replacement brake lining material is recommended for all vehicles to maintain the balance between front and rear brake performance. GM replacement brake parts have been carefully selected to provide the proper brake balance for the purposes of stopping distance and control over the full range of operating conditions. Installation of front or rear lining material with performance different from that of recommended GM replacement parts can change the intended brake balance of this vehicle.

  1. Raise the vehicle and support the vehicle with safety stands.
  2. Mark the relationship of the wheel to the hub.
  3. Remove the tire and the wheel.
  4. Mark the relationship of the drum to the axle.
  5. Remove the drum.

 



 

  1. If the drum is difficult to remove, do the following:
    • Make sure the parking brake is released.
    • Back off the parking brake cable adjustment.
    • Remove the access hole plug from the backing plate and insert a screwdriver through the hole to push the parking brake lever off the stop.
    • Use a rubber mallet to tap gently on the outer rim of the drum and/or around the inner drum diameter. Be careful to not deform the drum by excessive beating.
  1. Remove the actuator spring and the adjuster actuator.
  2. Raise the lever arm of the actuator until the upper end is clear of the slot in the adjuster screw.

 



 

  1. Slide the actuator (10) off of the adjuster pin (12).
  2. Disconnect the actuator spring (13) from the shoe (15).
  3. Remove the hold-down spring assemblies (8) and the pins.
  4. Remove the lower return spring (6).
    • Pull the bottom ends of the shoes apart.
    • Lift the lower return spring (6) over the anchor plate.
    • Allow the shoe ends to come together.
    • Release the spring.
  1. Remove the shoe and lining assemblies (1 and 15).
  2. Remove the upper return spring (5).
  3. Remove the adjusting screw assembly.
    • Do not damage the wheel cylinder boots.
    • Bring the bottom ends of the shoes together (overlap if necessary) so the upper shoe ends clear the wheel cylinder boots. Spread the bottom of the assembly to clear the axle flange.
  1. Remove the upper return spring (5).
  2. Remove the adjusting screw assembly from the shoes.
  3. Remove the retaining ring (16).
  4. Remove the pin (14).
  5. Remove the spring washer (3).
  6. Remove the parking brake lever (2).
  7. Inspect the wheel cylinder for signs of leakage.
  8. Inspect the brake drum for signs of scoring and machining tolerance.
  9. Replace any parts that show signs of discoloration from heat, stress, or wear.
  10. Inspect the threads of the adjuster screw (14) for smooth rotation over the full length.

 



 

  1. Using denatured alcohol, clean the following components:
    • The adjuster screw (14)
    • The nut (10)
    • The spring clip (9)
    • The adjuster socket (7)

INSTALLATION PROCEDURE



 

  1. Install the parking brake lever (2).
  2. Install the spring washer (3). The concave side of the spring washer should face the parking brake lever.
  3. Install the pin (4).
  4. Install the retaining ring (16).
  5. Install the adjuster pin (12) in the shoe (15) so the pin projects 6.8 to 7.0 mm (0.268 to 0.276 inch) from the side of the shoe web where the adjuster actuator is installed.
  6. Apply brake lubricant or equivalent to the threads of the adjuster screw (14) and inside diameter and face of the socket (7). Adequate lubrication is achieved when there is a continuous bead of lubricant at the open end of the adjuster nut (10) and the socket (7) when the threads are fully engaged.
  7. Install the upper return spring (5).
    • Lay the shoes (1 and 15) on a clean, flat work surface in the position they will be in when installed on the backing plate.
    • The shoe with the parking brake lever goes to the rear of the vehicle.

NOTICE: Do not over-stretch the upper return spring. Damage can occur if it is stretched to more than 204.2 mm (8.04 inches) .

  1. Install the adjusting screw assembly.
    • The adjusting screw assembly should engage the adjuster shoe (1) and the parking brake lever (2).
    • The spring clip (9) must face the backing plate.
  1. Lubricate the shoe pads on the backing plate with a thin coat of white lithium grease.
  2. Install the shoe and lining assemblies (1 and 15).
  3. Install the upper return spring (5).
  4. Install the adjusting screw assembly.
    • Do not damage the wheel cylinder boots.
    • Overlap the bottoms of the shoes so the upper shoe ends clear the wheel cylinder boots.
    • Make sure the upper shoe ends rest on the wheel cylinder piston ends.
    • Do not place the lower shoe web ends under the anchor plate until the lower return spring is installed.

NOTICE: Do not over-stretch the lower return spring. Damage can occur if it is stretched to more than 107.3 mm (4.22 inches) .

  1. Install the lower return spring (6).
    • Bring the ends of the shoe and lining assemblies (1 and 15) together over the anchor plate.
    • Hook the spring ends to the shoe web holes.
    • Spread the lower ends of the shoe and the lining assemblies to clear the anchor plate.
    • Position the shoes against the backing plate and release them.
    • Pull the spring into the groove at the bottom of the anchor plate.
  1. Connect the hold-down pins and the spring assemblies (8).
  2. Install the adjuster actuator (11) over the end of the adjuster pin (12) so the top leg engages the notch in the adjuster screw. NOTICE: Do not over-stretch the actuator spring. Damage can occur if it is stretched to more than 83 mm (3.27 inches) .
  3. Install the actuator spring (13). The free end of the adjuster actuator (11) must engage the notch of the adjuster nut.
  4. Connect the parking brake cable to the parking brake lever (2).
  5. Install the drum. Align the marks made during disassembly.
  6. Adjust the rear brakes.
  7. Install the tire and the wheel. Align the marks made during disassembly.
Customer: replied 4 years ago.
Hello, thanks for your reply. In the instructions sent , it mentions to bleed the brake pressure modulator valve first. My best guess is, this is done with a two man team with the key in the on position. The information sent dos'nt go into detail about bleeding the modulator. Is it possable that the modulator is stuck, sending pressure only to the front brakes? The rear brake pads have only been replaced once since '98, and even then they showed no wear. I have taken every brake line loose,from front to back and forced compressed air through every line, then reconected,then added new fluid,and rebleed the system and I still have a soft brake peddel.I must have air trapped between the rear brakes and the modulator,or the modulator is stuck. What are your thoughts?
Expert:  Tim's Auto Repair replied 4 years ago.

hi

anything is posable...will the brakes get tight if you pump tit 3 or 4 times and hold them?

Customer: replied 4 years ago.
hi, yes for a little while, with the key off. With the key on,no.
Expert:  Tim's Auto Repair replied 4 years ago.

if it will pump up and hold,,you still have air in the system..if not,,the master cylinder may be bad

thanks

Customer: replied 4 years ago.
I find it hard to beleive that a master cylinder is bad right out of the box! In the directions sent it dosent say how to bleed the presure modulator; with the key on or off.
Expert:  Tim's Auto Repair replied 4 years ago.

hi

the fluid will bleed through the modulator when you bleed the calipers/cylinders

thanks

Tim's Auto Repair, mechanic
Category: Chevy
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Experience: Have owned a repair shop for 25 yrs.
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