Bleeding the brakes means getting any and all air bubbles out of your auto’s brake lines. There are a number of web sites explaining how to perform this task, however most of them are incomplete. And some of the suggested procedures simply don’t work. I know because I tried them. In this post I will explain how to properly bleed your brake lines. If you follow the procedure detailed below, you will be certain that your brake lines are bled properly. If there are any air bubbles in the brake lines, the brake pedal will feel spongy and the brakes will not work. Note: if you have any other problems with your brakes, it will not be addressed here.
Throughout this procedure you have to make sure that the brake fluid reservoir is filled to the top. Some reservoirs have a dividing line in the middle, so you have to make sure both sides are full.
Find the master cylinder. There will be two metal tubes coming out of it: one for the front wheels, and the other for the rear wheels. We will work on them one at a time. The order is not important.
Get a towel ready and disconnect one of the metal tubes. A few drops of fluid may spill, that is fine. Close the hole on the master cylinder with your thumb and push the brake pedal down. Either the brake fluid or air will come out. As you release the brake pedal you should feel a vacuum suction on your thumb. If air is coming out of the master cylinder as you push down the brake pedal, that means there is air inside and you could pump the brake pedal all day long without anything changing. We have to fill the master cylinder with the brake fluid. The master cylinder may be in perfect working order, but it needs to be primed with the brake fluid before it can push the fluid into the brake lines.
Normally the master cylinder should never have air in it. However, one way this could happen is if the reservoir emptied out for some reason. Even if you fill the reservoir with brake fluid, now the air is trapped in the master cylinder and the brakes will not work. Another way this could happen is if you dismantled the master cylinder like I did and installed it back without filling it with brake fluid first. Yet another way is the simple passage of time (over number of years).
What you have to do is this: as you are pushing the pedal down put your thumb down on the hole lightly so the air or the brake fluid can escape freely. Catch any fluid that comes out with your towel. As you are releasing the brake pedal, seal the hole with your thumb. If the air can not get in, the fluid from the reservoir will be sucked into the master cylinder. Repeat this process 6 to 8 times. If you still don’t see any fluid coming out of the hole, get somebody else (or yourself if you can access it) to put pressure on top of the brake fluid in the reservoir. I put about 5 to 8 psi of pressure into the reservoir. This pressure will push the brake fluid into the master cylinder and will cut down on the number of times you have to pump the brake pedal.
After the master cylinder fills up with the brake fluid, reconnect the metal tube, and refill the reservoir. You will know that the master cylinder filled up when you see lots of brake fluid coming out without any air bubbles.
Refill the reservoir and repeat the same procedure for the second metal tube. If the reservoir empties out, you will have to redo the process from the beginning.
It is now possible to follow the two person bleeding procedure widely documented elsewhere. Before we move on though, let me say that some web sites are suggesting that a vacuum pump be connected to the bleeding valve on the wheels. I tried this and I can tell you that this method does not work. The reason it does not work is that the master cylinder isolates the brake lines from the reservoir.
Start with the wheel furthest from the master cylinder, and continue with each wheel until all four wheels are done.
For each wheel do the following: connect a clear plastic hose to the bleeding valve. Let the person inside the car pump (push down and release) the brake pedal 5 or 6 times, and after the last push tell him to keep the brake pedal pushed in. You open the bleeding valve. You will see air bubbles mixed in with the brake fluid coming out of the valve. Close the bleeding valve and tell the person in the car to release the pedal. As the brake pedal goes up, more brake fluid will be sucked into the master cylinder. Wait for 5 to 6 seconds. Repeat the same procedure until you see hardly any bubbles coming out in the brake fluid.
Putting some pressure on top of the brake fluid in the reservoir will make this process faster since the pressure will help the brake fluid to travel into the master cylinder and from there into the brake lines.
That is all! Your brakes should be working fine now. In the rest of this post I will write about why I ended up working on the brake system of my car (all four wheels had drum brakes).
The picture above shows the two metal tubes coming out of the master cylinder. The two black hoses at the top carry the brake fluid into the master cylinder.
Another view of the master cylinder. It is hard to get a good picture because of all the other parts around it.
Linkage to Brake Pedal
This picture shows the brake pedal linkage to the master cylinder.
Flash Back About 4 Weeks
I had a one-of-a-kind kind of car. The brakes were gradually getting worse, and at some point I decided to take it to the brake shop. The closest one was Les Schwab Tire Center. I took my car there and the technicians worked on my car for about half an hour, took the tires off, refilled the reservoir, etc. But in the end, either they would not (or perhaps could not) work on this car. To their credit they did not charge me, however the brakes were exactly the same as they were before, no change whatsoever.
When I called the other brake shops, they asked me to bring my car to them, which meant towing. Then they would tell me if they could work on it. That was a losing proposition for me.
How hard could this be? I jacked up the right rear wheel and took out the wheel. There was a metal drum. I assumed that it contained the brake pads inside. When I pulled on it, it would not come out. I could not see any screws or bolts or nuts holding it, however I did not want to break it by prying it. I felt defeated and installed the tire back.
I talked to a number of people and they all said the same thing: just pull it, and it will come out. I was missing something. I jacked up the same wheel again, took the wheel off, and pulled out the metal drum. The result was the same, it would not come out. I was missing something. Suddenly it clicked and I realized that the handbrake was on. I released it. When I pulled out the drum, it just came out.
There was a lot of black dust and other debris inside. I cleaned it all. I had my son push down the brake pedal. I could see that the brake cylinder was pushing the pads away. There was a star shaped adjustment screw. I adjusted it so that the brake pads almost touch the drum outside then re-installed the wheel back on.
I did the same thing to the left rear wheel. When I test drove the car, the improvement was marginal. Not good.
I started to work on the front right wheel, then cleaned the black dust and debris. When I asked my son to push on the brake pedal, the brake pads were not moving at all. In fact the brake pads looked almost brand new. Obviously adjusting the brake pads would do nothing in this case. For a long time the front brakes were not used at all.
If the brake pads on the right wheel were not moving, where was the brake fluid going? I centered the jack in the middle of the car and removed both front wheels. I was sure that the brake pads on the left wheel would move, since the brake fluid is not compressible. When I had my son push down on the brake pedal, I could see that neither front pads were moving.
This explained the problem perfectly. Almost 70% of the braking power comes from the front wheels. Although I had fixed the rear brakes, the effect was not noticeable. I had no front brakes at all. When we brake, most of the weight of the car goes to the front wheels.
I tried to bleed the front brakes many times without success. That is why I thought that the problem was with the master cylinder. I took out the master cylinder, but could not see anything wrong with it, then cleaned it out and reinstalled it back. After all this work the brakes were now completely shot, front and back.
It turned out that the brake system just needed to be bled properly. After I did that as I documented in the first part of this post, the brakes worked great. In fact the brakes are now working even better than when I first bought this car.
The credit for this post also goes to Raif Suren and Necati Okyay for helping me out to solve this problem. Thank you both.