F-Twins Tech – F650/700/800 - Renewing Brake Fluid

[drneo66]

The articles, posts and comments in this tech section are posted by individual members and reflect their personal thoughts and experiences with repairing, maintaining, and generally working on motorcycles. This information may require specific knowledge and skills, may or may not be correct or current to model.

The authors of information found here and the BMW MOA take no responsibility for ensuring the accuracy of any information (including procedures, techniques, parts numbers, torque values, tool usage, etc.), or further for any damage of any kind or injuries incurred or caused by anyone following the instructions or information found here.

It is the duty of the individual to either assume the liability himself for responsibly using the information found here, or to take the bike or accessory to a Dealer or other qualified professional service.

Please ensure you dispose of your used chemicals, oils and fuels in an environmentally responsible manner. Most Auto Parts stores and service stations will accept used oil and lubricants, tires and batteries, please check for your local availability. Here's a link where you can look up a place to dispose of your used fluids (oil, coolant, brake fluid, etc.) - http://earth911.com/

This article, text and photos are Copyright of the individual authors and the BMW MOA, any copying or redistributing is permitted only by prior written authorization.

PLEASE PRINT AND READ ALL THE INSTRUCTIONS BEFORE BEGINNING!

Final note: PLEASE ONLY DO THIS JOB IF YOU ARE COMPETENT WITH TOOLS - Brake failure is no fun! When in doubt, take your motorcycle to a reputable dealer.

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Renewing the brake fluid in the front and rear brakes on your BMW twin-cylinder F650, F700 and F800.


The F-Twin manual calls for the brake fluid to be replaced every two years, and that's for good reason. Because brake fluid is hygroscopic, it naturally absorbs moisture from the surrounding air, which causes the boiling point of the fluid to decrease. A lowered boiling point could cause your brakes to fail (often at an inopportune time) because the liquid (which is not compressible) can turn to vapor (which is compressible) at higher temperatures. Brake fluid will absorb moisture whether you're riding 50,000 miles per year, or 5 miles.

DOT 4 brake fluid, which is recommended by BMW for our F-Twins, has a minimum boiling temperature of 446 degrees Fahrenheit when it's fresh out of the can. After absorbing just a small amount of water, that boiling temperature number can almost be cut in half. From what I was able to find, most DOT brake fluid will absorb about 3-4% moisture by volume after just two years. After the brake fluid absorbs about 8% of of it's total volume, the boiling point is almost no better than plain water.

The second reason that we want to replace the fluid in the brake system is because it also contains corrosion inhibitors. These inhibitors can prevent problems in our delicate ABS systems (if your bike is equipped). So, at the end of the day, a little $4 bottle of brake fluid can save you time, money, and possibly your life.



Note 1: The specific bike shown is a 2013 F800GS
Note 2: The 650 version of the F-Twins will only have one brake caliper and disc on the front wheel
Note 3: The tools and materials used are by personal choice and are not due to any affiliation with any brand


Tools Required:
- 11mm wrench
- Clear tubing that fits the bleeder nipple and small container or a vacuum bleeder (we will be using a Mityvac for this post)
- Torque wrench and 11mm socket
- Optional - T25 star (Torx) wrench or bit and ratchet

Materials Required:
- An unopened bottle of Dot 4 brake fluid
- Suitable bottle to hold used brake fluid for proper disposal


WARNING: Brake fluid attacks paint. Depending on the type of paint - the attack can be very fast, or relatively slow - but your goal in doing this job is to avoid getting brake fluid on any paint. IF you do get fluid on painted parts - a rinse with soapy water is a very good thing to do - as soon as you can. If you delay too long you'll be washing the paint off along with the fluid.

[drneo66]

Let's start with the rear brake. The rear brake reservoir is indicated by a green arrow.


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[drneo66]

I like to carefully unscrew the rear reservoir from the frame (using your T25 star bit) to make it easier to unscrew the cap and refill the master as needed. Make sure you put your least-favorite t-shirt around the reservoir as not to harm your paint. The cap simply screws off. There will be a plastic ring and a rubber stopper that will also need to be removed. Make sure you put these in a safe place as not to get brake fluid on any painted surfaces

I like to try to remove as much of the old fluid as possible from the reservoir before adding fresh new fluid. I use the MityVac to suck up this fluid, but you could also use a clean paper towel to carefully remove it. Just be careful as not to let any air into the system.

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[drneo66]

Next, we will remove the protective rubber cap from the rear brake. Take a moment to clean the area around the bleeding nipple, as we don't want to introduce any contaminants into the brake system.

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[drneo66]

We want to retract as much of the brake pistons back into the caliper as possible, as this will reduce the amount of brake fluid that's left in the caliper body. Most of the time you just need to use your hand to gently push the caliper against the brake disc. Alternatively, you can remove the caliper and use an appropriate tool to push the pistons back. The pistons live under the rounded portion of the caliper body, so pushing on the white "B" (on the caliper) towards the brake disc, should retract the piston into the caliper.

After that, we will hook up our bleeding equipment.

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[drneo66]

Start pumping the Mityvac to pull negative pressure, and then open the bleed nipple about an 1/8th of a turn, using your 11mm wrench. If you open the bleed nipple too far, you have the possibility to suck some air into the system, so again, don't open it too far. You should see some fluid begin to flow in the clear Mityvac tubing. Keep pumping the Mityvac until you have nearly removed all the the brake fluid in the rear reservoir. Again, make sure not to suck any air into the brake system. Always keep a vacuum on the system until you close the bleed nipple, if we don't, we have the possibility of adding air into the system. You will probably go through a bit of brake fluid doing this procedure, as the fluid has to travel from the reservoir, through the ABS pump (if equipped) through all the lines, and finally exit at the brake caliper. Always make sure you have a bit of fluid in the reservoir to prevent air entering the system (I can't type this enough).

If you don't have a vacuum bleeder, it will be a bit more work, but you can still flush the brakes. Having two people also helps. First, hook up the appropriately-sized tubing to the bleed nipple and submerge the other end in a bit of brake fluid (this reduces the chances of sucking air back into the system). Then, gently push down the brake pedal until you feel resistance. This will put pressure into the brake system. Open the bleed nipple about an 1/8th of a turn using your 11mm wrench. Brake fluid should start to flow and the pedal will travel further down its stroke. Try not to go all the way down and bottom out the master cylinder as this could introduce problems with the cylinder seal. Before releasing the brake pedal, close the bleeder nipple. Repeat this process - pressure, open, plunge brake pedal, close, pressure, etc. until you see fresh brake fluid exiting at the bleeder nipple.


Fresh, clean brake fluid is a very light honey color. The brake fluid that was flushed out of this bike was very dark, signifying how badly it was due to be changed.

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