Brake fluid is hygroscopic, that is to say it absorbs moisture from the air over a period. To ensure the absolute reliability of the brake system, the brake fluid must be renewed once a year by your BMW service station.
Bleeding the brake system
If the hand brake ever seems soft or 'spongy' when applied, the brake circuit must be bled.
Fill the brake fluid reservoir on the right handlebar (take off the cover with equalizing diaphragm after removing the 3 Phillips-head screws). Remove the dust cap from the bleed screw, connect the bleed hose and immerse it's free end in a vessel containing brake fluid. Apply the hand brake several times until braking pressure builds up.
At this stage, hold the brake lever on (pulling it up firmly) and at the same time open the bleed screw so that the remaining air can escape. Do not release the brake lever until the bleed screw has been tightened again.
Repeat this procedure until brake fluid emerges from the hose free from air bubbles, then finally tighten the bleed screw.
Warning: make sure that the brake fluid reservoir on the handlebar is kept topped up and not pumped dry, or else air will again penetrate the brake circuit.
Fig. 64 and 65
Note that all work on the brakes should be carried out only by an authorized BMW workshop.
Warning: see the 'Important Note' on page 15.