After talking to many owners, it would seem that there are more methods for bleeding brakes on a Porsche than there are cures for the common cold. Fortunately, I have polled many people and tried several different solutions, and I think that I have come up with the best compromise solution. This article is adapted from the original 914 brake bleeding article. However, the techniques documented in here are not appropriate for bleeding 914 brakes, as the 914 has that pesky hydraulic proportioning valve. For more information on bleeding 914 brakes, please see our Pelican Technical Article, Bleeding 914 Brakes.
There are currently three methods of bleeding the brake system:
- Pressure Bleeding. This is where you have a reservoir of brake fluid, and place a positive air pressure force on the opposite side of the fluid, forcing it into the brake system.
- Vacuum Bleeding. This is where you fill the reservoir, and then apply a vacuum at the bleeder nipple to pull fluid through the system.
- Family Member Bleeding.This is where you recruit the one family member or friend who owes you a favor and have them stomp on the pedal repeatedly until the entire system is bled. Note that this has nothing to do with the time that little Jimmy fell on the concrete and had to be rushed to the hospital.
The method that I've come up with combines the first and the third methods described above. Basically, I advocate bleeding the system with the pressure bleeder, and then using a family member to stomp on the pedal to free up the proportioning valve. 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 fill the system with brake fluid. Some people have suggested that colored brake fluid be used in order to determine when fresh fluid has been flushed through the entire system. I used a pressure bleeder like the Eezi-Bleed System shown in Figure 1. The system works by pressurizing a bottle filled with brake fluid from air in the spare tire. Inflate your tire to 20 psi, fill the bottle, attach it to the top of the reservoir (Figure 2), and then connect it to the spare tire. 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 tight garage. The probability of spilling on yourself and then leaning against your car is too great.
Now start bleeding the system. Start with the right rear caliper, the one that's located furthest away from the master cylinder. You will have to remove the rear wheels of the car to easily get to the rear caliper. 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 7mm wrench. A bleeder nipple is shown in Figure 3, 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 to make sure you have bleed the proportioning valve properly. 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:
- Right Rear Caliper
- Left Rear Caliper
- Right Front Caliper
- Left Front Caliper
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 with about a gallon of brake fluid. Depending upon your car, and the mistakes you may make, it's wise to have an ample supply.
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 valve at least three times. Repeat this entire procedure for all the valves in the same order as described previously.
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.
Be sure to rinse off brake fluid that has spilled on painted surfaces with water. Wiping it will only smear the paint more (I talk from experience here).
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Steven M. Stomski (Jstomski@aol.com) also has the following to add:
Recent postings re pressure bleeding brakes prompts this response. I too have found that pressure bleeding provides the best "pedal." I have had very little luck with the vacuum type (Mity Vac) and while pedal pumping certainly is thorough, an available SO or co-mechanic is not always an option (not to mention the trouble pumping your brakes during bleeding causes with your master cylinder!). The best pressure bleeders could end up costing several hundreds of dollars and likely will not deliver that much harder of a pedal.
My solution to the brake bleeding dilemma has been to fabricate a rather simple pressure bleeder. While I have been tempted to market this system, I am happy to outline the parts and the concept for my fellow Porsche wrenchers.
There are a couple of options for pressure source. As mentioned in other posts, a compressor is a good source of air, but not absolutely necessary. Some commercial systems (possibly the EZ system) use your spare tire as a compressed air reservoir and this could work for you as well. Any suitable storage tank can be used as well.
The most crucial difference in my system, compared to any other that I have seen, is the addition of an air filter. As we all know, brake fluid is hydroscopic (it absorbs water- definitely a no-no when it comes to brake fluid) and thus must be kept dry. Any compressed air will contain substantial amounts of H2O and thus must be filtered before using to pressure bleed. I simply install in line a "last chance" air filter, the type used when spray painting to keep the air dry (costs about $3 at any paint shop).
While the cap for the reservoir can be purchased, I simply used a spare cap, drilled it, and installed a tire valve. Other "options" in my system include an in line pressure gauge (while some people might think pressure bleeding is for "Chevys," if you keep the pressure low - around 10- 15 lbs., you won't have any problems. I also install a regulator valve/shut off.
The key to my system is to seal off the over flow and to NEVER let the reservoir run dry. One way to assure fluid in the reservoir at all times is to "bleed" with a small enough container that you have to empty regularly. Each time you empty the container (which should be smaller in capacity than the reservoir), shut the line off to the pressure, and top the reservoir off.
Enjoy- If any one has more suggestions, or comments (or needs further instructions), please let the e-mail, and brake fluid, flow.
In a message dated 98-09-22 Thom Fitzpatrick asked me what trouble pumping your brakes during bleeding causes with your master cylinder. Thanks for the follow-up Thom, I suspected someone would ask that question and should have dealt with it then instead of now, but here goes.
In "normal" use, the plunger/piston in a master cylinder probably only goes into the cylinder about 1/3 of the way or so. In part this is true because under "normal" use we don't really push the limits of pressure of the system and don't need the extreme pressure the MC can deliver. It is also true because under "normal" use when we use the pedal, the system is pressurized and we really can't push much further without some serious force. When racing, the system looses some of its effective pressure (OK, I am not an mechanical engineer, but boiled fluid, fluid with water or air, or trashy fluid can be compressed more than otherwise, right?). So, in racing, or when bleeding your brakes with the valves open, the piston can freely depress into the cylinder to the physical (non-pressure) limit of the MC. While new MCs have clean and smooth pistons, pistons on older MCs are prone to get dirty, and yes even rust or corrode. As the piston is depressed into the MC under normal braking, the seals and fluid help to keep that 1/3 or so clean, smooth, and well lubricated. The remaining 2/3s or so is exposed to the air and does not get the benefit of regular cleaning. When one depresses the piston when bleeding and the valves are open, the dirty 2/3s (no cigar comments, please) enters the cylinder and drags across the seals. While it might not be the worst thing in the world in general, the more dirt or corrosion on the cylinder or the more frequent and vigorous the pumping of the dirty piston across the seals, the worst the damage, which leads to a leaky MC.
Hope this helps.
Eezi-Bleed Pressure System
Brake Fluid Reservoir
Bleed Nipple (914 Caliper Shown)