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Pelican Technical Article:

Bleeding Brakes


2 hr






Vacuum brake bleeder, Pressure brake bleeder, Friendly assistant with a good right leg

Applicable Models:

Porsche 911 (1965-89)
Porsche 912 (1965-69)
Porsche 914 (1970-76)
Porsche 930 Turbo (1976-89)

Parts Required:

Brake fluid

Hot Tip:

Bleed your brakes with different colored fluid so that you know when all of your older fluid has been flushed through the system

Performance Gain:

Stiffer and safer braking

Complementary Modification:

Replace master cylinder, replace brake lines
101 Projects for Your Porsche 911

This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. 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 right tools are a necessary part of the job too. A few days before this book was to be sent off to my editor, I had a chance to evaluate a new type of pressure brake bleeder kit from Motive Products. Retailing for about $45, this kit attaches to the top of the master cylinder reservoir and applies pressurized air to the system. Brake fluid is forced out of the master cylinder reservoir and into the system. The pressurized kit is probably the best one around because it is the least likely to create air bubbles in the system. There was a time when no one was manufacturing pressurized bleeders, but thankfully Motive Products now supplies this excellent quality kit at a reasonable cost.

The pressurized system works very well because it pushes the brake fluid out of the reservoir and into the system. In this manner, it is very unlikely to create air bubbles in the system. When small air bubbles form in the brake lines, the entire system suffers as the brake pedal becomes soft. This is because air is much more compressible than the brake fluid. When you push on the pedal, the air trapped in the lines acts like a spring inside of the system. The air becomes compressed, absorbing energy from the system, instead of directing the energy towards pushing the caliper piston against the brake disc.

A second alternative is the vacuum bleeding kit. This kit works in the opposite manner of the pressure bleeder, applying a vacuum to the brake system in order to draw brake fluid out of the car. The system works well, but can sometimes cause air bubbles to form in the lines. Particularly on cars with rear brake proportioning valves like the Porsche 914, the vacuum system can leave air trapped in these valves, giving a spongy pedal as a result. When using the vacuum bleeding system, the best approach is to bleed each corner of the car several times, in order assure that all the air is out of the system. Simply fill up your brake reservoir, attach the pump system, pump up some vacuum, and then open the bleed nipple. Brake fluid should be pulled out of the system when the vacuum is applied. If it's not: you may have a problem with your brake lines.

The third and most labor intensive method of bleeding your brakes involves actually having an assistant press on the pedal while you go around to each wheel and bleed the system. Without a doubt, this is the most effective method of bleeding, and should probably be used as a final procedure when performing any brake system bleeding. This method actually pushes fluid through the system (similar to the pressure-fed system) at a high rate of velocity. Sometimes, air bubbles that are in the system can become dislodged and cleared out by the quick rush of brake fluid when you press on the brake pedal.

The procedure for bleeding the brakes using the brake pedal is pretty straightforward. Attach a small rubber hose to the brake caliper nipple and let the other end hang inside an empty container. Ask your assistant to firmly and quickly press on the pedal 3 times, and hold it down the third time. Then, open up the bleed nipple by unscrewing it slightly. Brake fluid should come rushing out and the pedal should sink to the floor. Make sure that your assistant doesn't remove his or her foot from the pedal, as that will suck air back into the system. With the pedal still depressed to the floor, tighten up the bleed nipple. When the nipple is closed, have your assistant remove their foot from the pedal.

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.

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. 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.

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 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 âwet.' 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.

When you are bleeding the system, start with the wheel that is farthest away from the master cylinder, and then work your way back towards the front left wheel. In other words bleed the system in this order: right-rear, left-rear, right-front, left-front. Bleeding in this order will minimize the amount of air that gets into the system. Always bleed each caliper more than once, because bleeding the other calipers can dislodge air into the system. You might be surprised that after 5 times around the car there still might be a little bit of air in the system. A good rule of thumb is the more you bleed, the better your brakes will be.

Make sure that you use DOT 3 or DOT 4 brake fluid in your car. Some of the later model 911s with anti-lock braking systems required 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.

One of the most popular vacuum brake bleeding kits is the MityVac kit.
Figure 1

One of the most popular vacuum brake bleeding kits is the MityVac kit. This kit contains a hand operated vacuum pump and a variety of attachments to allow it to fit just about any car. The pump draws brake fluid using vacuum pressure created by the hand pump. This photograph shows the process of emptying the system of brake fluid, prior to removing a brake caliper.

Shown here is the pressure bleeder kit from Motive Products.
Figure 2

Shown here is the pressure bleeder kit from Motive Products. This brand new 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. Retailing for about $45, the bleeder kit is a very useful and cost-effective tool to have in your collection.

Comments and Suggestions:
Alex Comments: When using the Motive pressure bleeder make sure to check the braided lines, grommets & plastic couplers coming from the reservoir to the master cylinder before you pump up the pressure. It took a couple times of mopping up my floorboard before I traced a crack in the rear plastic coupler. After I replaced the coupler the pressure bleeder worked great.
January 7, 2018
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
steve911T Comments: Fred, many years later, clamp it off with a hemostat.
October 29, 2017
  Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
max Comments: brake lights do not come on...have a 1970 Porsche 911..should i replace the switch on pedal first? thx
July 21, 2017
  Followup from the Pelican Staff: Check if it has voltage and if the voltage is being switched, if not, replace it. Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
Rhswiele Comments: When pressure bleeding 911 Carrera 3.2s 1984-89 at least you need to clamp off the vent line from the master cylinder reservoir. This is so pressure can be maintained by the pressure bleeder.
June 12, 2017
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
tirwin Comments: This article should probably be updated to reflect the fact that the colored brake fluids such as ATE Super Blue are no longer legal in the U.S. The Federal Motor Vehicle Safety Standard says that brake fluid must be clear or amber, so colored brake fluids are no longer produced. It was a great idea while it lasted though.
November 25, 2016
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
Andy uk Comments: I am restoring a 1965 porsche 912 and I am having trouble bleeding the brake system. I have bleed it several times but still have to pump the pedal several times before you get any presure.
Any advice would be most appreciated.
September 10, 2016
  Followup from the Pelican Staff: Sounds like a faulty master cylinder. - Nick at Pelican Parts  
Toddgibbs Comments: Sorry - forgot today what car! 1979 930. Front brakes

June 3, 2016
  Followup from the Pelican Staff: I am not 100%. Give our parts specialists a call at 1-310-626-8765. They can tell you the size. Maybe you can find out there once you know it. - Nick at Pelican Parts  
Toddgibbs Comments: Great thanks Nick. I'm also struggling to find the rebuilt kit in the UK. Can you tell me the piston size? Is it 38mm or 43? Thanks!
June 3, 2016
  Followup from the Pelican Staff: I am not 100%. Give our parts specialists a call at 1-310-626-8765. They can tell you the size. Maybe you can find out there once you know it. - Nick at Pelican Parts  
toddgibbs Comments: Hi, I want to rebuild my calipers. I assume I have to drain the system - what is the best method? I don't mind draining as I would like to replace the brake fluid anyway.

June 2, 2016
  Followup from the Pelican Staff: You can open the bleeders, then let it gravity bleed out into containers until empty. - Nick at Pelican Parts  
bill Comments: In replacing brake fluid in my 911sc, can I use DOT4 fluid or must I use DOT3 as recommended in original 1980 handbook
August 12, 2014
  Followup from the Pelican Staff: You can use DOT 4 is you want to. - Nick at Pelican Parts  
Tom Comments: What is the best pressure bleeder kit for a 2011 Carrera coupe?
May 20, 2014
  Followup from the Pelican Staff: This one works well: - Nick at Pelican Parts
Airhead89 Comments: I was warned by a mechanic to NOT use a pressure bleeder on these older cars as the reservoir could crack or burst from being old and brittle. He had one blow brake fluid everywhere with only 10 psi in the system. Many of the sources I have researched recommend the pedal pump system on the older cars. The general consensus is that there is just no getting around this in terms of safety and reliability.
April 26, 2014
  Followup from the Pelican Staff: I disagree. This seems like a very rare circumstance - I've never heard of it happening. If the reservoir is likely to fail, then it's most likely to develop a crack that will loose pressure slowly - not blow up like your mechanic described. - Wayne at Pelican Parts  
Ryan Comments: Just rebuilt all 4 calipers and installed a new master cylinder with new stainless lines. Brake pedal still sinks to the floor after bleeding the car twice using motive Ez bleed? Pressure used was 10 psi. Is this too low? Could this be the reason my brakes are spongy and hitting the floor? Car I'm referring to is a '74 911. Thanks
January 27, 2014
  Followup from the Pelican Staff: There may be air trapped. I would fill master cylinder, let each wheel gravity bleed. Then bleed the brakes, starting at the right rear with help from an assistant. - Nick at Pelican Parts  
Fred Comments: My 1973 911T has an overflow tube on the brake fluid reservoir. Does this mean that I cannot use a pressure bleeder?
June 15, 2013
  Followup from the Pelican Staff: If you cannot seal the reservoir, you will not be able to use a pressure bleeder. - Nick at Pelican Parts  

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Page last updated: Mon 1/22/2018 02:01:26 AM