MODEL | 460, 461.217/219/227/229/238/239/249/266/267/302/321/322/323/326/327/328/329/331/332/335/336/337/338/341/342/345/365/366/367/368/392/401/402/403/404/405/450/451/452/454/455/456/458/459, 463 up to 5/31/12 |
Shown on model 461.392 |
4.1 | Brake unit |
4.2 | Master brake cylinder |
P42.10-2932-11
Location
The brake unit is located on the left side in the engine compartment at the firewall.
Task
Increase of force at the brake pedal and actuation of the flange-mounted master brake cylinder.
A special maintenance service is not required.
General function
The brake unit is a device that supports the pedal force, which uses the pressure gradient between the generated vacuum and the atmospheric outer pressure as a source of power. The brake unit is a twin-diaphragm unit. It has 2 consecutively arranged working pistons and a twin-diaphragm. This location of the working pistons doubles the working piston space.
Release position shown |
A | Vacuum |
B | Atmospheric pressure (outside air) |
P43.10-0216-12
Function in release position
When in released position, the outside air duct is closed and the vacuum duct is open. The same vacuum is present on both sides of the working piston. The compression spring holds the working piston in its right rest position.
Shown on partial braking |
A | Vacuum |
B | Atmospheric pressure (outside air) |
C | Reduced vacuum |
P43.10-0217-12
Function in partial braking
When the brake pedal is actuated, the vacuum duct is first closed and then opened during the further course of movement of the outside air duct. The vacuum behind the working piston is released until the master brake cylinder pistons, the push rod and the valve piston come to a standstill through the hydraulic pressure generated in the master brake cylinder. The pressure is transferred through the reaction disks. At the same time, the poppet valve is placed on the valve piston, thus interrupting the outside air supply.
A standby position is now reached, where any slight change in the pedal pressure causes increase or decrease in the pressure differential on both sides of the working piston. This leads to an increase or decrease in the braking ratio.
Shown on full brake |
A | Vacuum |
B | Atmospheric pressure (outside air) |
P43.10-0218-12
Function with full brake
When in full brake position, the vacuum duct is closed and the outside air duct is constantly open. Thus, the maximum possible pressure differential exists on both sides of the working piston. This leads to maximum possible support. Further increase in force on the main master brake cylinder pistons is only possible through increase in the pedal force.