Brake servo assembly (Brakes)

Brake servo assembly

The brake servo assembly provides power assistance to reduce the pedal load when braking.

The assembly is attached to the front of the pedal box and comprises a circular housing containing a diaphragm, push rods, valve and filter. A push rod at the rear of the housing is connected to the brake pedal. The vacuum line is connected to a port in the front face of the housing.

With the brake pedal released and the engine running, vacuum pressure is present on both sides of the diaphragm. When the brake pedal is pressed, the rear push rod moves forward and opens the valve to allow atmospheric pressure through the filter into the pedal side of the diaphragm. The pressure differential acting on the diaphragm increases the pressure being applied by the brake pedal, which is transmitted to the master cylinder via the forward push rod.

If the servo fails, the hydraulic system will still function but will require greater pedal effort due to the lack of vacuum assistance.

Sectioned view of brake servo assembly

1. Housing
2. Control valve
3. Rear push rod
4. Filter
5. Diaphragm
6. Forward push rod