It is recommended to use a special installation for bleeding hydraulic drives under pressure, for example "ARC 50". If you do not have one, you can bleed the brake system by pressing the brake pedal. In this case, an assistant is needed. The efficiency of this method is lower, and labor costs are greater than when using a special installation.
When bleeding the brake system, make sure there is fluid in the reservoir, and do not allow its bottom to become exposed.
Before you start bleeding, eliminate the influence of the vacuum booster by pressing the brake pedal several times.
Remove air first from one circuit, then from the other, starting each time from the wheel furthest from the master cylinder, observing the following sequence: brake cylinders of the right rear, left rear, right front and left front wheels.
Add brake fluid to the reservoir to the normal level.
Remove the protective caps from the air outlet fittings. Clean the fittings from dust and dirt.
On disc brakes, place a transparent tube on the top nipple head and lower its free end into a container partially filled with clean brake fluid. Unscrew the nipple by 1/4 turn. After this, the assistant should slowly press the brake pedal and slowly release it, while the fluid along with the air will be forced out of the system through the hose into the container. Repeat this process until the bubbles stop coming out and clean fluid starts coming out of the hose. Hold the pedal pressed and tightly screw the nipple to release air. Remove the hose and put a protective cap on the nipple.
Repeat the operations, unscrewing the lower fittings one by one, starting with the inner fitting.
Repeat the operations for the other wheels.
Bleeding air from the rear wheel drum brakes is done in the usual way.
After bleeding, restore the brake fluid level in the reservoir if necessary.
(Read the original source on the website BMWMan)