This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.
Bleeding brakes is not one of my personal favorite jobs. There seems to be a bit of black magic involved with the bleeding process. Sometimes it will work perfectly, and then other times it seems like you end up with a lot of air in your system. The best strategy to follow when bleeding your brakes is to repeat the procedure several times in order to make sure that you have removed all the trapped air from the system.
The basic Boxster brake system with anti-lock brakes (ABS 5.3 and 5.7 without PSM) can be bled using traditional methods. For cars with traction control or Porsche Stability Management (PSM), you need to use the Porsche System Tester 2 (PST2) in order to activate the valves in the hydraulic unit during the bleeding process. If your car has a "PSM off" switch on the dashboard, then you will need to go to a shop that has a PST2 so that the brake system can be bled properly.
There are currently two popular methods of bleeding the brake system, pressure bleeding, and vacuum bleeding. Pressure bleeding uses a reservoir of brake fluid that has a positive air pressure force placed on the opposite side of the fluid, which forces it into the brake system. Vacuum bleeding is where you fill the reservoir, and then apply a vacuum at the bleeder nipple to pull fluid through the system.
The method that I've come up with combines the first method described above and yet another third finishing method. Basically, I advocate bleeding the system with the pressure bleeder, and then use a family member to stomp on the pedal to free up any trapped air in the system. If the family member really owes you big time, you will be the one stomping on the pedal, and they can spill brake fluid all over themselves.
The first step in bleeding your brakes is to jack up the car and remove all four wheels (see Pelican Technical Article: Jacking Up and Lifting the Boxster on Jack Stands). The next step is to fill the system with brake fluid. I recommend using colored brake fluid like ATE SuperBlue in order to determine when fresh fluid has been flushed through the entire system. One of my favorite tools for pressure bleeding is the Motive Products Bleeder. 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. Retailing for about $50 online from PelicanParts.com, the bleeder kit is a very useful and cost-effective tool to have in your collection.
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 to about 25 psi using the hand pump. This will pressurize the system. 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. Bleed the right rear caliper by attaching a hose to the bleed nipple, placing it in a jar, and then opening the valve by turning the bleeder nipple counter-clockwise with an 11mm wrench. Let the fluid flow 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 (see Figure 3). 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. The Boxster calipers have two bleed nipples: bleed the outer ones first.
When no more air bubbles come out, then move to the next caliper. Bleed them in this order: right rear caliper, left rear caliper, right front caliper, left front caliper. Bleeding in this order will minimize the amount of air that gets into the system.
Repeat the process 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, I recommend having an ample supply. Also, only use new brake fluid from a sealed can. Brake fluid is hydroscopic, meaning that it attracts water and water vapor, which diminishes its performance. Brake fluid containers left exposed to air will have the fluid inside compromised after a short period of time.
If you had to replace the master cylinder, or if the system needs a large amount of fluid, then supplement the bleeding process by opening up the right rear nipple, and then pressing down on the brake pedal 2-3 times. Slowly release the pedal. Repeat for the other three corners of the car.
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 in to 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 it doesn'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 (see Pelican Technical Article: Brake Line Replacement).
Now, 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.
For cars with the standard ABS 5.3, the bleeding method detailed here works very well. If you find that your ABS equipped car feels spongy on the brake pedal, take the car to a deserted parking lot and engage the ABS system by stopping short a few times. Then go back and rebleed the system: it should take care of the spongy pedal.
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 then done - don't bleed the system in a tight garage. The probability of spilling on yourself and then leaning against your car is too great. 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. It's a smart idea to fill your reservoir (green arrow) 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 4 brake fluid in your car. The use of silicone DOT 5 fluid is not recommended for street use, and never mix DOT 4 and DOT 5 fluid together or severe component corrosion can occur. Shown here is the Motive Products Power Bleeder. Available for about $50 from PelicanParts.com, it is a huge time-saver when it comes to bleeding your brakes.
Open the bleed nipple by loosening it in the caliper by about a quarter of a turn. If you can fit a flare-nut wrench over the bleed nipple, then I recommend using one, to help avoid rounding out the nipple. Let the brake fluid run out of the caliper until no more bubbles appear (inset). 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 or sitting in your Power Bleeder for a while. 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 can result in a spongy pedal.
There is a relatively new product out called Speed Bleeders. These small caps replace the standard bleeder valves located on your calipers. The Speed Bleeders have a built-in check valve that eliminates the need for a second person when pedal bleeding the brakes. Simply open the bleeder valve for a particular caliper and step on the brake pedal. The Speed Bleeder will allow brake fluid to cleanly bleed out of the system without sucking air back in. When used in conjunction with a pressure bleeder system, you can achieve a pretty firm pedal bleeding the brakes by yourself. I still recommend using the two-person pedal-stepping method as a final procedure, simply because the high pressure from this method can help to unclog trapped air bubbles.