Vacuum Brake Booster: Description and Operation
Brake Booster
COMPONENT LOCATION - 5.0L SUPERCHARGED
NOTE:
LHD (left-hand drive) installation shown, RHD (right-hand drive) installation similar
COMPONENT LOCATION - 5.0L NATURALLY ASPIRATED
NOTE:
RHD (right-hand drive) installation shown, LHD (left-hand drive) installation similar
COMPONENT LOCATION - TDV8
NOTE:
LHD (left-hand drive) installation shown, RHD (right-hand drive) installation similar
OVERVIEW
Power assistance for the brakes is provided by a vacuum operated brake booster. Vacuum is produced by an engine driven vacuum pump.
VACUUM PIPES
Plastic vacuum pipes connect the brake booster to the vacuum source. Check valves are incorporated into the vacuum pipes.
On gasoline vehicles the connection with the brake booster contains a check valve to maintain the vacuum in the brake booster. An in-line check valve near the connection with the intake manifold prevents air being drawn from the intake manifold and fuel vapor from entering the pipes.
On TdV8 vehicles there is a single check valve integrated into the vacuum pipe connection with the brake booster. The check valve maintains a vacuum in the brake booster when the engine is running at low speeds, and the vacuum pump is operating at less than the optimum.
BRAKE BOOSTER
The brake booster provides power assistance to increase the braking effort applied by the driver. 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 protrudes through an aperture in the bulkhead and is connected to the brake pedal.
The vacuum pipe is connected to a port in the front face of the brake booster housing.
With the brake pedal released and the engine running, a vacuum 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 both sides of the diaphragm increases the pressure being applied by the brake pedal.
In the event that the brake booster fails, the hydraulic system will still function but will require greater pedal effort due to the lack of vacuum assistance.
VACUUM PUMP - V8 5.0L
The vacuum pump is a mechanically driven vane pump installed on the front of the engine sump body and driven by the auxiliary camshaft. Two bolts attach the vacuum pump to the sump body. A seal is installed in a groove on the mating face of the vacuum pump.
The vacuum pump drive gear locates on the end of the rotor and engages with slots in the front of the auxiliary camshaft. An oil tube in the center of the rotor supplies engine oil from the auxiliary camshaft to lubricate the vacuum pump. Exhaust air from the vacuum pump is expelled into the engine sump through the sump body.
VACUUM PUMP - TDV8
The Vacuum required for brake booster operation on TdV8 vehicles is provided by an engine driven vacuum pump. The vacuum pump is a radial vane type pump mounted to the front of the RH (right-hand) cylinder head which is driven by the intake camshaft. The vacuum pipe from the brake booster connects to an elbow on the rim of the vacuum pump.
The vacuum pump is lubricated and cooled by engine oil supplied to a port in the front face of the vacuum pump from a gallery in the cylinder head. The oil return is through a vent in the front face of the pump into a drain cavity in the cylinder head. Air extracted from the brake booster is vented into the drain cavity with the returning engine oil.
The vacuum pump is also used to supply vacuum for operation of the following components:
- The EGR (exhaust gas recirculation) system. For additional information, refer to Electronic Engine Controls Description and Operation
- The adaptive engine mounts. For additional information, refer to Electronic Engine Controls Description and Operation