BMW recommends you change the brake fluid every two years. It’s not a very complicated procedure but you do have to be careful, as it can be messy and easily mess up your paint if you get any of car. My 2011 BMW E92 M3 had just reached the end of its 4-year maintenance included plan and a service indicator stating it was time to change the brake fluid had been going off for a week. So I thought it would be a good DIY project for the weekend.
Why Change The Brake Fluid
The main reason for every other year brake fluid flush that it’s hygroscopic. Big word, just means that brake fluid will absorb moisture from the atmosphere, lower its boiling point and effectiveness if you drive on the track. The water in this fluid can also damage the brake master cylinder over time if not regularly flushed. BMW says the brake fluid needs to be flushed every 2 years, and that’s fine for road cars but will need more frequently for cars that get taken to the track. Interestingly, our first service on our long-term BMW i3 will need a brake fluid flush at two years of age and that’s the only reason for going in for service.
How To Change The Brake Fluid
First up is to remove all the wheels. If you don’t have access to a lift, you can do one wheel at a time starting with the rear passenger wheel.
Next I like to remove all the brake fluid out of the brake master cylinder as possible. I use a small 10cc syringe and was able to remove about 300 milliliters out.
Some people use an old turkey baster but I find these don’t hold on to the fluid as well and are more apt to splash brake fluid all over the place.
The brake master cylinder hides on the drivers side in the E9X chassis under the hood close to the base of the windsheild.
Once the three 8mm bolts are removed, take out the cabin air filter housing and lay to the side. Two of 8mm bolts are up by the windshield and one closer to the front. Make sure all three are out before trying to remove the cabin air filter housing or you might break the cabin air filter housing. I miss old BMW’s, just lift hood and see the master cylinder.
After I take out as much brake fluid as I can, I fill it to the top with fresh DOT 4-brake fluid.
Fresh unopened brake fluid is key. If they’ve been opened, the brake fluid can start absorbing water from the atmosphere. I like the BMW Dot 4 fluid if it’s not going on the track soon, or will use MOTUL RBF 600 if I am headed to a track event as it has a higher boiling point – 593F vs 446F.
Next you can either use a pressure bleeder like I did this time or you can get a buddy to pump the brake pedal, pressuring the system. Some track guys swear by the manual brake pedal pump over the pressure bleeder.
Once the braking system is pressurized, open up the bleeder screw on the brake caliper. I use a tube so there is a solid column of fluid coming out and no change that air will be entrained into the braking system.
Start with the passenger rear brake caliper, then the driver rear caliper, followed by the passenger front and lastly the drivers front. You need to make sure the brake reservoir stays full so you don’t force air onto the system from the master cylinder. That would be a nightmare, IMHO, and require a ton of bleeding to get all the air bubbles out. I’ve never done it. I just check the level after each caliper is flushed. I usually have to add fluid after the two rear ones.
When you are done make sure the fresh brake fluid is at the correct level before you put the cap back on. Re-install the cabin air filter housing, put your wheels back on and torque the wheels. I like wheel studs, which you can see poking out of the wheel hubs. I use cooper anti-seize on the hubs as it makes taking the wheels off the next time easier. I torque the wheels down to 88 lb-ft with a large torque wrench.
Last, you need to reset the service indicator via pushing a small button to the bottom left of the RPM gauge and cycling through the services with the left stalk and BC button. I watched about 3 vids on youtube to do it and am still not totally sure how I did it as the sequence is different if you have service due soon or service required warning on you check control.
Tools
- Jack Stand or 9,000lb 2 Post lift
- 17mm Socket to remove wheels
- 8mm socket to remove cabin air filter housing over brake master cylinder
- Socket driver
- 10cc syringe, or turkey baster to remove old brake fluid
- Brake Pressurizer or friend to pump break pedal
- 9mm wrench – opens bleed screw rear caliper
- 11mm wrench – opens bleed screw front caliper
- 2 unopened bottles of brake fluid DOT 4 BMW or your favorite brand
- Reservoir to capture old brake fluid.
- Lots of disposable shop towels to keep brake fluid splash to a minimum
- Shop light
- Copper anti-seize for wheel hubs
