Contents: Vacuum tubes ⇩ Brake booster ⇩ Vacuum pump (4.0 l and 4.4 l) ⇩ Vacuum pump (2.7L diesel engine) ⇩
A vacuum brake booster provides increased brake performance. On gasoline models, the vacuum is created by the intake manifold and an electric vacuum pump. On diesel models, the vacuum is created by an engine-driven vacuum pump.
Vacuum tubes
Plastic vacuum lines connect the brake booster to the vacuum source. The vacuum lines have check valves built into them. On gasoline models, there are two check valves built into them that maintain pressure in the brake booster when the throttle is open and the vacuum pump is not running, and also prevent fuel vapors from entering the brake booster. On diesel models, there is one check valve built into the vacuum line connection to the brake booster that maintains pressure in the brake booster when the vacuum pump is not operating at its optimum level.
Brake booster
The brake booster is installed in the engine compartment on the driver's side, on the engine bulkhead.
The brake booster is a dual diaphragm design with a 7.0:1 ratio. The input rod is connected to the brake pedal. The output rod enters the master piston of the master brake cylinder. A vacuum tube is installed in a bushing on the front of the housing and connects the brake booster to the intake manifold and an electric vacuum pump. (for models with petrol engine) or a motor driven vacuum pump (for models with diesel engine).
Vacuum pump (4.0 l and 4.4 l)
| Item name | Spare part catalog number | Description |
| 1 | - | Anti-vibration support |
| 2 | - | Pump cover |
| 3 | - | Vacuum pump inlet |
| 4 | - | Rubber cover for the outlet |
| 5 | - | Electric motor cover |
| 6 | - | Electrical connector |
On gasoline-powered models, an electric vacuum pump supplements the main vacuum supply from the engine manifold.
The vacuum pump is mounted on a support bracket in the left front corner of the engine compartment. Two vacuum pump anti-vibration mounts are mounted on the support bracket studs and secured with nuts.
The vacuum pump is a radial vane pump driven by an electric motor. The rotor and vanes of the pump are made of self-lubricating carbon-based material. A branch pipe is installed on the inlet of the pump, designed to connect the vacuum tube from the brake booster. A second branch pipe with a rubber casing is installed on the outlet of the pump.
The vacuum pump is controlled by the Engine Control Module (ECM), which supplies power to the vacuum pump via the vacuum pump relay in the battery junction box (BJB). The ECM regulates the vacuum pump ON time and has built-in overload protection.; for example, to prevent excessive continuous operation of the pump, a minimum permissible delay is set between its activations.
Vacuum pump (2.7L diesel engine)
| Item name | Spare part catalog number | Description |
| 1 | - | Vacuum connection (not used) |
| 2 | - | Vacuum connection of the brake booster |
| 3 | - | Drive |
| 4 | - | Sealing |
| 5 | - | Oil inlet hole |
| 6 | - | Oil drain/vent hole |
A vacuum pump is installed on diesel engine models because the intake system does not create sufficient vacuum for satisfactory operation of the brake booster.
The vacuum pump is a radial vane pump mounted on the rear of the right cylinder head and driven by the exhaust camshaft at half the engine crankshaft speed. The brake booster vacuum pipe is connected to the crankshaft connection on the rim of the vacuum pump.
The vacuum pump is lubricated and cooled by engine oil supplied to the hole on the front surface of the vacuum pump from a channel in the cylinder head. The oil returns to the drain channel of the cylinder head through a vent hole on the front surface of the pump. Air taken from the brake booster is supplied to the drain channel together with the returning engine oil.
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