When you press the brake pedal, the pusher presses on the two pistons of the master brake cylinder, which through the brake booster form pressure in the system.
The master brake cylinder cannot be repaired. If it fails, it must be replaced as an assembly. The pistons transmit the pedal force via a hydraulic line to the brake calipers.
The caliper pushes the wheel cylinder piston, which in turn presses the lining against the brake disc. When the pedal is released, the piston returns to its original position and the pads move away from the disc. The distance between the pads and the disc leaves 1 mm, but this is enough for the disc to rotate freely.
Pic. 6.1. Scheme of a brake actuator with a diagonal separation of circuits
Vacuum brake booster
The vacuum brake booster reduces the force on the brake pedal, making it easier to drive. The vacuum amplifier uses a diaphragm, on both sides of which a vacuum is created during normal operation. During braking, air is supplied from one side of the diaphragm, forming atmospheric pressure. Due to the difference in pressure transmitted through the diaphragm, the pusher moves in the direction of rarefaction (vacuum), providing auxiliary force for braking. When the brake pedal is released, air is pumped out of the amplifier cavity through the control valve, creating a vacuum.
Pic. 6.2. Vacuum brake booster
Master brake cylinder
The master brake cylinder is used on dual-circuit brake systems. The front right and rear left brakes are actuated by the primary piston, while the front left and rear right are actuated by the secondary piston. The brake master cylinder combines the functions of a standard dual brake master cylinder plus a low brake fluid indicator and brake pressure regulator.
Pic. 6.3. Master brake cylinder
Pressure regulator
The pressure regulator limits the output pressure to the rear brakes after the pressure reaches the limit value in the master brake cylinder. The adjuster is used when less force is needed on the rear brakes to achieve optimal braking.
Brake fluid level sensor
The brake fluid level sensor, located in the brake fluid reservoir, turns on the BRAKE warning light when it detects a low fluid level. As soon as the brake fluid reaches the correct level, BRAKE goes out.
Fittings and pipelines of the brake system
Connection of pipelines between the brake master cylinder, brake calipers and hydraulic unit is carried out by means of threaded fittings with metric threads.
Pic. 6.4. Identification of fittings of the brake system: A - the shape of the tips of steel or copper tubes; B - the shape of the threaded recesses in the nodes; C - fittings with six outer faces of 11 mm each
Brake fluid
Brake technology and in particular disc brakes (hollow pistons that transfer little heat, little fluid in the cylinder, floating calipers that eliminate the need for a relatively large supply of working fluid in the least cooled part of the wheel), to minimize the risk of «steam locks» even in the case of frequent and prolonged use of the brakes (in the mountains). However, the performance of the brake fluid deteriorates somewhat during the first months of operation due to the slight absorption of moisture. This necessitates the replacement of the brake fluid.