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Dr. Hamman
Dr. Hamman, Chevy Technician
Category: Chevy
Satisfied Customers: 6286
Experience:  30 Years Experience repairing, customizing, and building chevys.
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Chevrolet Malibu: 2001 Chevy Malibu - Brake pedal goes to the

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2001 Chevy Malibu - Brake pedal goes to the floor after changing pads and rotors, when car is running.

For the second time, after changing front brake pads and bleeding the system, the brake pedal will press all the way down when the car is running, but will be firm when the engine is off. The first time, I just pressed the calipers back and thought I had damaged the master cylinder in the process, and replaced a perfectly good master cylinder. I had a friend come over with a pressure bleeder and we bled the system repeatedly. (MC was properly bench bled before installing) The brakes slowly got better over time.

This time, the brake pedal was firm when we started. I opened the bleeder valves when removing the calipers so I wouldn't force fluid backwards through the system. Replaced pads and rotors. I knew we'd have to bleed the wheel cylinders, and did. Immediately, the same symptom occurs. When the engine is running, the brake pedal can be pushed to the floor with little stopping power.

We did 20 repetitions of hold the brake pedal down, release the bleed valve, close the bleed valve, re-pump the brakes. Again, pedal is very firm when the engine is off.

ABS and BRAKE lights are OFF on the dash.

Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice so we may have to fine tune the answer. Feel free to add any additional info you feel is needed as we go on. Always keep in mind that I am here to help you with any questions.

The 2001 Malibu's I have worked on have had rear drum brakes. With the symptoms you have you either have air in the brake system, or the rear shoes are not tight enough. Tighten the rear shoes as tight as you can get them, and bleed the brakes and see if the pedal is good with the engine running. If it helps back the rear shoes off just enough where they just lightly drag. If you have 4 wheel disc, then the problem has to be air in the system. Sometimes even a bench bled MC can still have air in it. The way you get stubborn air out is to remove the brake lines from the MC and hold your fingers over the holes where the brake lines go. Then pump the brake pedal slowly. Your fingers act like reed valves and wont let air back in, while forcing liquid out. This will purge any air out of the MC. Sometimes an antilock systems will retain air, the best way to get that out is to stomp the brake pedal to the floor, with the bleeder open. The huge rush of pressure will move air out that gentle pumping wont. I would put a piece of hose on the bleeder, and put it in a can. When you push the brake pedal hard, the fluid can spray, and make a mess. Give this a try and see if you can work through this. If you have any more questions, as always, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer.

I do not get paid for my work unless I am given 3 - 5 stars/smile faces. If the answer is not clear, let me know what additional help you need, and I will assist you further. A bonus and positive feedback are always appreciated, good luck and Thanks.

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Customer: replied 4 years ago.
Re-bled the entire system starting at the MC. Much better, although not perfect. Last time this happened, things got progressively better over time. If it doesn't, I'll bleed again. I think the ABS traps air. I tried to avoid that by opening the bleed valves when pushing the caliper back. Maybe the reservoir ran low while the valves were open. My son was taking care of that, so I don't know what it looked like. That would have allowed air into the MC.

On the plus side, he has a complete change of brake fluid again.

Thanks for the help.
Good luck with it, and thanks for using Just Answer.