Brake Bleeding 2000 Malibu

[Fishinguy40]

I replaced the master cylinder. It was bench bled before install. New front pads. Rear shoes are still good. I attempted to bleed the ABS module but some of the fittings started to gall and strip. I had to remove all brake line from the ABS module to rework one of the fittings. I then bled it as best I could. I don't want to attempt to bleed at the ABS again because I would probably have to replace the module and lines. I bled brakes at all wheels. Take for a drive and works good until I stand on the brakes and ABS kicks in. Then pedal goes to the floor. I bleed all lines again at the wheels and same thing. Works good until I stand on the brake and ABS kick in. I assume as the solenoids cycle they are passing air into the system. I don't have a scan tool to do the auto bleed procedure on the ABS module. I'm wondering if I will eventually bleed all air out by what I am doing. Drive, engage ABS and bleed again. If so, how many times will it take? If not, how much would it cost to have a shop do the auto bleed on the ABS?

[Jeremy airjer W]

The first mistake was attempting to bleed the ABS. It is not necessary even when replacing the master cylinder.

[Fishinguy40]

Airjer,

Where did I go wrong? Here is the procedure I used, from Alldata DIY.

Also, I do not see any bleeder screws on the ABS Modulator.

Manual Bleeding Procedure

Notice: Avoid spilling brake fluid on any of the vehicle's painted surfaces, wiring, cables, or electric connectors. Brake fluid will damage the paint and the electrical connections. If any fluid is spilled on the vehicle, flush the area to lessen the damage.

Important: This procedure may require the help of an assistant to apply the brake pedal while the bleeder valves are opened and closed.

Important: Ensure that the master cylinder brake fluid level does not drop to the bottom of the master cylinder reservoir. You will be instructed to Inspect and fill the master cylinder reservoir at times during this procedure. However, the actual frequency of master cylinder reservoir filling REQUIRED will depend on the amount of fluid that is released. If the brake fluid level drops to the bottom of the master cylinder reservoir, start the bleed procedure again at Step 1.

1. Inspect and fill the master cylinder reservoir to the proper level as necessary. Refer to Master Cylinder Reservoir Filling. Important: Use a shop cloth in order to catch escaping brake fluid.

2. Slowly open the ABS modulator brake pipe fitting (1) starting from the first pipe on the left side in order to allow the brake fluid to flow.

3. Press and hold the brake pedal approximately 75 percent of a full stroke. Notice: Refer to Fastener Notice in Service Precautions.

4. Close the ABS modulator brake pipe fitting when air bubbles are no longer detected in the brake fluid.

o Tighten the ABS modulator brake pipe fitting to 24 Nm (18 ft. lbs.) .

5. Repeat Steps 2 and 3 for the remaining ABS modulator brake pipe fittings.

[Jeremy airjer W]

I don't know.

You never need to bleed the ABS module unless you replace. Otherwise don't touch it. It doesn't matter if you run the entire brake system dry, or replace every brake component the ABS module will never need to be bled. So I'm not sure why you decided to bleed the ABS module in the first place?

[Fishinguy40]

I bled the ABS module because Alldata said to, as the above procedure shows. Also, if you should never have to bleed the ABS module, why does the procedure you provided include steps to bleed it?

I guess I will just keep bleeding at each wheel brake.

[Jeremy airjer W]

alldata and mitchel are not always 100% correct. Anybody that uses these will confirm this.

I'm just trying to shed some light on ABS systems. There seems to be a myth that they need bleeding anytime the brake system is bled as part of the repair or maintenance of a brake system which is not true.

If the brake system is operating enough to engage the ABS system under hard braking than I would have to believe that the brakes are working correctly and properly bled. If there was air in the brake system the pedal would be spongy and would likley not supply enough pressure to lock up the brakes.

If the pedal goes to the floor with the ABS engaged and the vehicle still stops than one of two things is happening. Either the ABS is working properly and you don't have enough experience with the proper operation of the ABS under a hard brake situation or there is a problem with the ABS (which could have been present before you started your repairs or a result of your repairs).

In my experience with active ABS it does feel like the pedal is dropping as the ABS system takes over. The ABS system operates by taking over the braking system and rapidly dumps the fluid pressure provided by the brake system and supplies its own fluid pressure. This depressurizing and pressurizing of the brake system is the HUM that you hear when the ABS is active. Overactive ABS gives the best example of this as the pedal drops at slow speeds it feels like there is no brakes. Other than the ABS being active when it is not supposed to be the feeling the ABS gives under this condition when it is active is normal although unsettling when you need to stop.

So I have to wonder whether you are interpreting the ABS functioning properly as the ABS functioning incorrectly or if there really is a problem?

[Fishinguy40]

The brakes did feel firm and car stopped well until I floored the brakes and got the ABS to engage. After the ABS had been engaged, the brakes would be soft again and the pedal would go to the floor. Not during engagement of ther ABS.

I did get everything to work. After driving and engaging the ABS, I bled brakes at each wheel. I did this a total of three times. I now have a firm brake pedal, even after the ABS has been engaged.

Hopefully this thread will help somebody else on what to do and what not to do. Glad I could provide a "teachable moment" for others.