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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12892
Experience:  Have owned a repair shop for 25 yrs.
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what causes air (foam)in the brake lines when bleeding front

Resolved Question:

what causes air (foam)in the brake lines when bleeding front brakes on a 1997 chevrolet suburban 4x4?
Submitted: 5 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 5 years ago.

hi

did it do this before you worked on it?did you break a beader to push the calipers back?can you not get a full pedal?

thanks

Customer: replied 5 years ago.
please excuse my spelling. to answer your ?s. no,no and no. in the begining i replaced only the front pads and rotors. i jacked up and supported the front of the vehical i then removed the front wheels then removed one caliper. i opened the cap to the master brake cylinder and pushed the pistons to the calipers back to make room for the new pads checking the resivor to make sure it didn't overflow. then i installed new rotor, loaded the new pads and remounted the old caliper. i then repeted the same proceedure on the other side. then i tried to bleed the brakes but bleeder valves did not cooperate. one vavle broke and the other was plugged solid. needless to say the brake fluid was way bad and needed replace. i then desided at this time to replace the rear wheel cylinders the front calipers and the master cylinder. after bench bleeding the master cylinder. i installed all the new parts and proceeded to bleed the hole brake system starting with right rear, left rear, front right then front left. the pedal never felt hard, but i tried a short test drive anyway in a very safe area. the cars front brakes got hot, to the point you can smell the pads. i brought the car back and tried to bleed the hole system again. thats when i noticed that the rear brakes blead fine while the fronts had alot of air in the form of foam. now i'm lost. in my mind the only thing left is the a.b.s. module but i'm not sure if it's rebuildable or if i have to replace it which the cost is out of my reach at this point. any help is much apperciated thanks tom usher.
Expert:  Tim's Auto Repair replied 5 years ago.

hi

i think that you still have air in the syatem......make sure the the rear brakes are adjusted all the way against the hub.....if the front brakes are getting hot,if you are not useing the brakes much,,this may be from bad rubber lines[that connect to the caliper]these will calapse on the inside sometimes,makeing them work like a check valve,not letting the brakes release....sometimes these can be hatefull to get the air out of..

thanks

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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.
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12892
Experience: Have owned a repair shop for 25 yrs.
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