The first step in bleeding your brakes is to fill the system with brake fluid. Some people have suggested that colored brake fluid (ATE SuperBlue) be used in order to determine when fresh fluid has been flushed through the entire system. I used a pressure bleeder like the Motive Products Bleeder. This product is a step above its now-defunct precursor, the EZ-Bleed system. The system has a hand pump that you can use to pressurize the brake fluid to just about any pressure. A small gauge on the front of the brake fluid reservoir indicates the pressure of the brake fluid inside. The very large reservoir can hold about two quarts of brake fluid – more than enough for most brake flushing and bleeding jobs.
The system bleeds by pressurizing a bottle filled with brake fluid from air from an internal hand pump. The procedure is to add fluid, attach the bleeder to the top of the reservoir cap, and pump up the bleeder bottle using the hand pump. This will pressurize the system. Note: brake fluid is highly corrosive and will mar paint very easily. Bleeding your brakes is a messy job; keep yourself away from the paint and don't bleed the system in a tight garage. The probability of spilling on yourself and then leaning against your car is too great. Check to make sure that there are no leaks around the bleeder, or where it attaches to the top of the master cylinder reservoir.
Now start bleeding the system. Start with the right rear caliper, the one that's located furthest away from the master cylinder. You should remove the rear wheels of the car to easily get to the rear caliper. The whole process is a much easier if the car is off of the ground, and the wheels have been removed. The front wheels can be turned for access to the calipers. Bleed the right rear caliper by attaching a hose to the bleed nipple, placing it in a jar, and then opening the valve with a wrench (a 7mm wrench is typically needed). A bleeder nipple, and can be opened by turning it counter clockwise. Let the fluid out until there are no more bubbles. If you don't have a pressure bleeder system, you need to find someone to press on the pedal repeatedly to force fluid through the system. Another solution is to get a check valve and place it on the nipple while you stomp on the pedal. This will work for getting fluid into the system but you will still need a second person for the final step - to make sure you have bleed the system completely. If your rear caliper has two bleed nipples (some have one, others have two), bleed the lower one first.
When no more air bubbles come out, then move to the next caliper. Bleed them in this order:
(Bleeding in this order will minimize the amount of air that gets into the system).
Repeat until you can no longer see any air bubbles coming out of any of the calipers. Make sure that you don't run out of brake fluid in your reservoir, or you will have to start over again. It is wise to start out with about a 1/2 gallon of brake fluid in the pressure bleeder, and another 1/2 gallon on the shelf in reserve. Depending upon your car, and the mistakes you may make, it's wise to have an ample supply.
During the bleeding process, it’s very easy to forget to check your master cylinder reservoir. As you are removing fluid from the calipers, it will be emptying the master cylinder reservoir. If the reservoir goes empty, then you will most certainly add some air bubbles into the system, and you will have to start all over. Keep an eye on the fluid level and don’t forget to refill it. Make sure that you always put the cap back on the reservoir. If the cap is off, then brake fluid may splash out and damage your paint when the brake pedal is released. If you are using a pressure bleeder system, make sure that you often check the level of brake fluid in the bleeder reservoir so that you don’t accidentally run dry.
If you are installing a new master cylinder, it’s probably a wise idea to perform what is called a dry-bleed on the workbench. This is simply the process of getting the master cylinder full of brake fluid and ‘wet.’ Simply add some brake fluid to both chambers of the master cylinder, and pump it a few times. This will save you a few moments when bleeding the brakes.
Now, make sure that all the bleeder valves are closed tightly. Disconnect the pressure system from the reservoir. Now, get your family member to press down repeatedly on the brake pedal at least five times, and then hold it down. Then open the bleeder valve on the right rear caliper. The system should lose pressure, and the pedal should sink to the floor. When the fluid stops coming out of the bleeder valve, close the valve, and then tell your family member to let their foot off of the pedal. Do not let them take their foot off until you have completely closed the valve. Repeat this motion for each bleeder valve on each caliper at least three times. Repeat this entire procedure for all the valves in the same order as described previously.
I recommend that you use this procedure as a final step, even if you are vacuum or pressure bleeding. The high force associated with the pressure from the brake pedal can help free air and debris in the lines. If the brake fluid doesn’t exit the nipple quickly, then you might have a clog in your lines. Brake fluid that simply oozes out of the lines slowly is a clear indication that your rubber lines might be clogged and constricted. Don’t ignore these warning signs – check out the brake lines while you are working in this area.
Then, let the car sit for about 10 minutes. Repeat the bleeding process at each corner. The pedal should now feel pretty stiff.
If the pedal still feels spongy, make sure that you have the proper adjustment on your rear calipers or drum shoes. Also, you may need a new master cylinder, have a leaky caliper, or have old spongy flexible brake lines.
Another important thing to remember is that brake fluid kills – paint jobs that is. Brake fluid spilled on paint will permanently mar the surface, so be very careful not to touch the car if you have it on your hands and clothing. This of course, is easier said than done. Just be aware of this fact. Rubber gloves help to protect yourself from getting it on your hands and your paint. If you do get a spot on your paint, make sure that you blot it with a paper towel - don’t wipe or smear it. It’s also important not to try to clean it off with any chemical or other cleaning solutions.
There are few little tricks that you can use when changing your brake fluid. The company ATE makes a brake fluid called SuperBlue that comes in two different colors (Figure 6). It’s a smart idea to fill your reservoir with a different colored fluid, and then bleed the brakes. When the new colored fluid exits out of the caliper, you will know that you have fresh fluid in your system. Make sure that you use DOT 3 or DOT 4 brake fluid in your car. Some of the later model BMWs with anti-lock braking systems require the use of DOT 4. The use of silicone DOT 5 fluid is not recommended for street use.
You should also routinely flush and replace your brake fluid every two years. Deposits and debris can build up in the lines over time and decrease the efficiency of your brakes. Regular bleeding of your system can also help you spot brake problems that you wouldn’t necessarily notice simply by driving the car. Also, never reuse brake fluid - always use new fresh fluid. In addition, don't use brake fluid that has come from an empty can that has been sitting on the shelf. The brake fluid has a tendency to absorb moisture when sitting on the shelf. This moisture 'boils' out of the brake fluid when you start using the brakes, and results in a spongy pedal.