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Written 3/26/2005

After making any changes to your car's braking system, you should make sure you are getting full effectiveness from it. Whether it be new pads, rotors, or an entire brake upgrade, the brakes are the most important safety feature of your vehicle. Life sucks without them... This page describes how to bleed/flush the brake system and then how to bed your brakes.

If, for any reason, you have opened the brake fluid system to open air, from replacing calipers/lines to running the master cylinder dry, etc, you need bleed the system to remove air bubbles. See BLEEDING YOUR BRAKES below. This section also applies to changing out your system with new fresh fluid. Brake fluid is hygroscopic, which means it absorbs water. Over time, your brake fluid will literally suck water out of the air and become less effective over time (hence the terms wet and dry boiling points on a bottle of brake fluid, dry is when it is new, wet is after it has absorbed water). When brake fluid gets too hot from extreme driving, it can actually boil and create its own bubbles. This leads to very soft and even unusable brakes. New "dry" fluid keeps the boiling point high and this is why brake systems should be flushed with new fluid every year or so.

If you have recently replaced pads, rotors, or both, you need to bed in the new pads to the rotors. See BEDDING YOUR BRAKES below.

1 - Quart of NEW, UNOPENED brake fluid, best you can get
1 - About a foot of 1/4" rubber hose such as vacuum line
1 - Tall open container for catching used brake fluid
1 - A friend or two

11mm Wrench

IMPORTANT: If you run your master cylinder dry (Photo A), you have to tow the car to a BMW dealer to have them refill and bleed the ASC/DSC/ABS circuits. Do not let this happen. Try to have a friend keep an eye on the fluid level in the master cylinder during the entire procedure and top off as necessary. You should leave the master cylinder cap off during bleeding, just avoid getting contaminants inside. Also, a word on "pressure bleeders"... I'm not a fan, so if you are, use their included instructions and ingore what I am about to write.

NOTE ON CHANGING FLUID: If you are changing out your brake fluid completly, the process is not to different from below. The only differences are that you may want to suck as much of the old fluid from the master cylinder without emptying it. Add the new fluid, such as ATE Super Blue, to top off the master cylinder. Then follow the instructions and bleed each caliper until the new blue fluid appears. ATE also makes Super Gold, same fluid, just a different color so you can go back and forth and know when the new fluid has reached the calipers.

1. Start with right rear wheel. The idea is to start as far from the master cylinder and move closer as we go. This means RR, LR, RF, then LF.

2. Remove the wheel and find the bleeder screw, usually at the very top of the caliper (Photo B). Stock floating brakes will have one bleeder screw. Fixed calipers like my Brembos will have two (if you have two, do the outside one first).

3. Remove the rubber protective cap on the bleeder screw and attach the length of rubber hose (Photo C).

4. Place the other end of the hose into you catch container and fill the container with enough fresh brake fluid to keep the hose submerged. We don't want to allow air to go back into the system (Photo D).

5. Have a friend sit in the vehicle and pump the brake pedal a few times to get it firm. Using an 11mm wrench, slowly open the bleeder screw releasing the bubbles and old fluid into the container. When the brake pedal reaches the floor, close the bleeder.

6. Repeat this process until you get no more bubbles coming out of the hose. It may take a few times to get it all out.

7. Once you are not getting any more bubbles, tighten the bleeder, remove the hose, and replace the protective cap (if needed).

8. You are set. Move onto the next wheel in the sequence - RR, LR, RF, LF. Remember! Keep an eye on your fluid level in the master cylinder.

9. Once you finish the LF brakes, check for leaks and correct brake operation. The pedal should be firm and not soggy. SLOWLY, go out and carefully drive the car to check for solid brake feel and no pulling or lack of braking force.

10. You're done!

1 - A whole lot of open straight road


After installing any new rotors or pads, it is imperative that you bed the pads into the rotors. This is a relatively easy process, but most do it wrong or never at all. Follow these steps to bed your pads:

1. Find an area where you have plenty of room and very little traffic.

2. Bring the car up to 60 mph and use normal braking to slow to 5-10 mph. Do not stop. Repeat 3-5 times. This brings the brakes up to operating temperature.

3. Bring the car up to 60 mph and stop as HARD as possible without locking up the wheels or engaging ABS. DO NOT COME TO A STOP. Repeat 3-6 times. This burns off the protective layer on the pads and rotors and leaves a layer of pad friction material on the rotors. You may smell the hot brakes, this is perfectly normal and expected.

4. Drive the car normally for 10-15 minutes without touching the brakes. Do NOT stop. This is the cooling down period. If you stop, you may leave an imprint of the hot pad on the rotor and this will cause a vibration like a warped rotor.

5. If done correctly, your rotors should have a cool gray/blue color from the heat cycle. If you need to, let the brakes completely cool and repeat the process. You can also do this bedding procedure at any time in the future if your pads need it or you want to restore good braking power.

You're done!

NOTE: Are you using upgraded aftermarket pads/rotors/calipers, and want more initial bite in your braking? If you can do it safely and legally, you can wait for the brakes to cool completely from the procedure above and then repeat it, but in step 3, do it 3 times from 100mph instead. Leave a little more time to let them cool in step 4 and you should be good to go.


Photo A

Photo B

Photo C

Photo D

  © MarvelPhx