The presence of air is signalled by the "sponginess" of the brake control and poor braking efficiency.
Caution! Considering the danger for vehicle and rider, it is strictly necessary, after refitting brakes and restoring the braking system to the regular use conditions, that the hydraulic circuit be air purged. The vehicle must be on level ground to be purged. While purging the hydraulic system, fill the reservoir with the necessary quantity of brake fluid. Check that, during the operation, there is always brake fluid in the reservoir.
Remove the rubber protection cover from the bleed valve.
Insert the transparent plastic pipe in the rear brake calliper bleed valve and insert the other end of this pipe into a container to collect the fluid.
Remove the rear brake oil reservoir cap.
Quickly press and release the rear brake lever several times and then keep it fully pressed.
Loosen the bleed valve 1/4 of a turn so that the brake fluid flows into the container. This will release the tension on the brake lever and will make it reach the end of stroke.
Close the bleed valve before the lever reaches its end of stroke.
Repeat the operation until the fluid draining into the container is air-bubble free.
Note. While purging the hydraulic system, fill the reservoir with the necessary quantity of brake fluid check that, during the operation, there is always brake fluid in the reservoir.
Screw the bleed valve and remove the pipe.
Top-up the reservoir until the right brake fluid level is obtained.
Refit and lock the rear brake oil reservoir cap.
Refit the rubber protection cover.
See also specifications for this operation.