I'm about to throw in the towel on my spongy brake problem. This is my last attempt to get a suggestion to resolve it. If you guys can't lead me to the answer, I'll have to take it to the shop.
I was driving my 2001 Buick Regal one night when the brake pedal suddenly went down to the floor. Drove it carefully back home.
Here's what I've done to try to resolve it myself:
- Checked the master cylinder and all four wheels for leaks. Didn't find any.
- Replaced the master cylinder.
- Bled the master cylinder. I used an approach I found on youtube here:
If you don't want to watch, it basically involves running a fluid line from the front driver caliper directly to the master cylinder. Pumping the fluid through that line allows the air to escape the system until you end up with a closed loop of fluid only.
- Bled each wheel with a bleeder bottle:
https://www.1aauto.com/how-to-bleed-your-brakes-by-yourself/video/11656
- For each bleed point, I kept pumping the brakes until I didn't see any air bubbles in the line.
- Made sure that I kept the master cylinder topped off.
I've done this bleed method twice, but I've still got spongy brakes.
What did I miss or do wrong?
Did you in anyway adjust your rear brakes ?
Nothing done to anything except the master cylinder.
No leaks at wheels so where did the brake fluid leak from? A brake pedal that suddenly drops would indicate to me a sudden fluid leak. Did you quit looking before you saw where the fluid ran out? No leak along the frame?
A brake line with a hole would let air re-enter the brake lines and not allow pumping the lines full. Neighbor across the street has a steel brake line that wore a hole and had the same symptoms you describe. He didn't see fluid on car because fluid sprayed away from frame and body parts. Not all leaks are at major parts.
You should just try it this way...get someone to pump the brakes and then you bleed. Make sure that person whom pumps the brakes does it slowly and tells the pedal is down. The pedal should firm up as it starts to compress the air in the system. Open bleeder and close quickly when the stream of brake fluid slows down. Repeat that on the other side. Check your fluid in the Master C.yl. You may have to start the engine so that the ABS is activated after the initial bleeding. For maximum brake pedal height you should adj the rear brakes. Just rotate the tires and click the adjuster to till you hear the drum touching the brake drum. Do they same on the other side. Now step on the brake to make the rear shoe self center and adjust themseves to the drum. Repeat the previous. technically what I do is adjust them till the wheel does not move anymore. That insures and tells me that their is no hydraulic movement in the wheel cylinders thus insuring when everything is right that pedal is as firm as its going to get. But after wards you have to use a screw driver and brake tool to back off the adjuster whcih can be a hassle for some people. As far as external leaks...did you see any indications of a fluid leak? If not then more than likely the original MC bypassed inside. But we have a NEW MC and must deal with it not consider the old MC in our solution here.
some possibilities:
- air trapped in ABS system. You have to visit a shop for this.
- Worn out/faulty brake flex lines.
- leak somewhere in the brake system. Sometimes they rust out.
There is air trapped inside of the master cylinder.
Master cylinder MUST be bled off the vehicle. Both reservoirs of the cylinder must be bled...one is for front brakes and other for rear brakes.
The air bubbles can be microscopic in size. You must bleed until absolutely no bubbles appear. This process includes short stroking the master cylinder (like pumping your brakes) and holding the pushrod in for 20-30 seconds (like holding pressure on brake pedal).
You may of already damaged the replacement master cylinder. In use, there is a very short stroke of the brake pedal pushrod to activate the brakes.
If, in the bleeding process you tried already, you pushed the brake pedal to the floor, you have ruined the internal seal of the master cylinder.
Final Verdict - bad brake line between the ABS module and the firewall. Replaced that and everything else was fine. Bleed method was fine, but was not going to work until the lines were solid.
Thanks for those steering me in the right direction.