This article is one in a series that have been released in conjunction with Pelican Parts' new book, How to Maintain and Modify your new MINI The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 500+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any MINI owner's collection. The book is due to be released in late 2015. See The Official Book Website for more details.
Bleeding brakes can be an extremely frustrating job. 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 the brake 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
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. In this article we will focus on pressure bleeding.
The first step in bleeding your brakes is to fill the system with brake fluid. I recommend ATE Super Gold (part 706232-M4). One of our 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 up to 30psi. However, in the case of the MINI, I don't recommend exceeding 25psi as this can cause the reservoir to rupture and probably spray brake fluid everywhere.
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 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. Make sure that the seal on the inside of the reservoir cap is seated correctly as well.
Now start bleeding the system. Start with the right rear caliper, the one that's located furthest away from the master cylinder. The whole process is much easier if the car is off of the ground (See our project on jacking up the car for more info), and the rear wheels have been removed. The front wheels can be turned for access to the calipers, however, if you don't want to lift the front end. Bleed the right rear caliper by attaching a clear plastic hose to the bleed nipple, placing it in a jar, and then opening the valve by turning the bleeder nipple counter-clockwise with a 9mm flare nut wrench. Watch the fluid in the clear line for air bubbles. Keep the bleeder valve open until all air bubbles have disappeared, then close the valve.
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. The idea here is to build up pressure in the system, then crack the bleeder valve open to release the air pushed to the caliper. Typically, you want a helper to press the pedal hard until pressure builds up at the pedal and then have the helper hold the pedal down. At this point, open the valve. The pressure exerted on the pedal will force the air out.
Another solution is to get a set of Speed Bleeder valves. These are caliper bleed valves that have a check valve built in. A great solution that allows you to keep the bleeder valves open indefinitely. They only allow air and brake fluid to flow out, preventing air from re-entering the system. The upside to this solution is that you do not need to build up pressure in the system. You just need to make sure that the reservoir is constantly full of fluid. Note: If your caliper has two bleed nipples (some may have one, others may 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. 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.
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. Another important note here is that when the system is pressurized, you want to slowly open the pressure bleeder reservoir first. This will relieve the pressure on the system and will draw fluid back into the reservoir.
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 ÃÂ¢ÃÂwet.' 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 as it eliminates any air pockets that will be inside the cylinder.
Now, make sure that all the bleeder valves are closed tightly. Disconnect the pressure system from the reservoir. Now, get your helper 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 our project on replacing brake lines).
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.
There's one caveat to the whole bleeding process: if you run the reservoir dry, you won't be able to bleed the system with a pressure bleeder or by stomping on the pedal as you will have introduced air into the ABS pump. BMW Recommends the use of a specialized computer system to trigger the ABS pump into what is called ÃÂ¢ÃÂbleed mode'. This mode cycles the pump to purge the air out. In our case, the AutoEnginuity software was able to access the ABS system and trigger the system.
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 re-bleed the system: it may take care of the spongy pedal, although this not a factory recommended procedure and it may not eliminate all the air from the system.
Another important thing to remember is that brake fluid kills paint. 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. 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. Shown here is the Motive Products Power Bleeder, attached to the brake fluid reservoir (yellow arrow). 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. Let the brake fluid run out of the caliper until no more bubbles appear. 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. 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 valves 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 on the caliper and pump the brake pedal. The Speed Bleeder will allow brake fluid to cleanly bleed out of the system, without sucking air back in. When used with a pressure bleeder system, you can achieve a firm pedal bleeding the brakes by yourself.