BMW R850 Maintenance Manual page 43

Close the bleeding nipple while fluid is STILL COMING OUT and BEFORE the reservoir
is empty, (4) Add more fluid to the reservoir and start this cycle again. Memorize step
#3.
The brake nipple is located on the caliper body. Stand to the left side of the bike and
look at the front wheel. The tire is mounted on the rim. The brake disc (rotor) is smaller
than the rim, made of shiny metal with holes bored in it. At the one o'clock position there
is a black metal caliper with the word "BREMBO" in metallic relief on the body. A rubber
hose containing the brake fluid is attached to the top of the caliper. Also on the top of
this black caliper is a rubber cap that covers the metal nipple. The nipple sticks up, has
a hole in its center, is smooth and round at the top and the base is a six-sided bolt.
Remove the rubber cap and clean the nipple before using it.. When the nipple bolt is
rotated (looking down at it) counter-clockwise it becomes loose and brake fluid may flow
out of the brake system through the center hole.
Position the bike and secure the handle bar so that the handle-bar reservoir is level with
the ground or slightly tilted so that the hose connection is the lowest point. Using an
11mm box end wrench or socket to open the nipple may help prevent problems if it is
very tight. Start on the left front caliper (furthest from the reservoir). Open the reservoir
top.
Step one: Attach the Mityvac suction hose to the nipple and pump the tool to create
suction. Make certain the reservoir on the tool is attached and the tool is functioning;
and you might even try reading the manual for the tool. Pump the tool to create a
vacuum. Consider the following: You may wish to seal the nipple-hose connection area
with grease so that ambient air is not sucked into the hose. In this way, if there was no
air in the brake system there will be no air in the spent fluid cup. Many mechanics don't
seal the nipple-hose connection with grease because air in the spent fluid does not
affect the bleeding procedure, they do not mind seeing the air bubbles because the
spent fluid will be discarded and they do not check it for bubbles, and therefore they
consider greasing the nipple as an unnecessary bother.
Step two: Slowly and carefully open the nipple and observe the fluid level in the bike
reservoir carefully. When you look at the hose that is attached to the nipple you will see
bubbles in the hose. The bubbles are from air being sucked into the line around the
nipple area as well as any air that may be in the system. Step three: When the amount
of fluid in the reservoir decreases by 50%, turn off the flow by tightening the nipple
(clockwise). As you are tightening the nipple, the Mityvac must still contain some
vacuum , some fluid flow must be taking place so that air can not enter the system, and
the reservoir must contain some fluid. Step four: Add brake fluid when 50% or more of
the fluid has been vacuumed (drained, suctioned) from the bike reservoir. Repeat these
four steps until the fluid appears clear in the tube leading to the Mityvac reservoir jar.
When the fluid is clear, tighten the nipple and replace the rubber cap. Move to the right
front caliper of the bike and repeat the four steps until the fluid appears clear again.
When finished with the right side, replenish the brake reservoir and replace the cap and
screws. Fluid should be at the top of the reservoir site window.
Move to the rear disk and bleed the rear reservoir from the nipple on the rear caliper until
the fluid is clear. Replace the rubber cap on the nipple, replenish the reservoir and
replace the cap on the rear.
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