Your Vacuum Pump worn out? » Read more about common malfunctions • Repair • Replacement manual
Double the brake force with the vacuum pump
The brake booster is a technically simple, yet very effective component of a hydraulic brake system. It uses the normal ambient pressure to double the pressure on the master cylinder. It requires a permanently maintained vacuum to do so. This is where the vacuum pump comes into play. Yet, it doesn't just serve to supply the brake booster with a vacuum. In today's modern engines, there are many more applications for a vacuum, which can be controlled with the help of the vacuum pump and the connected vacuum cans, such as:
- Turbocharger control
- Supply air control
- Exhaust gas control
- Control of the exhaust gas return valve
Where is the vacuum pump located?
The vacuum pump is located in close proximity to the brake booster. Usually, it is installed directly on the cylinder head. The proximity to the brake booster is necessary to ensure that as little vacuum as possible is lost to the supply lines. The brake booster is easy to find in the engine compartment. It is the thick black box that is mounted directly on the bulkhead. The brake pedal that protrudes into the passenger compartment is also located at the brake booster. When this pedal is stepped on, it opens a valve through which air enters into the brake booster, thus pushing down on the piston of the braking pressure distributor or main cylinder.
From a technical viewpoint, there are different vacuum pump designs. We distinguish between membrane vacuum pumps and impeller vacuum pumps. In membrane vacuum pumps, a rubber membrane moves back and forth to create airflow. Here, the desired vacuum is produced with the help of flaps and valves. Impeller vacuum pumps feature a rotating actuator that creates the desired vacuum by means of adjustable work spaces.
The vacuum pump is powered by discs, belts, cams, tappets or gears. Oftentimes these sit directly on the cylinder head and are directly powered by the camshaft. The fact that is is mounted directly on the cylinder head also has the advantage that the vacuum pump can easily be lubricated by means of simple channels. Vacuum pumps mounted separately of the cylinder head are usually provided with permanent grease lubrication. The vacuum pump's power-operated mechanism of action is the reason a brake booster fails when the motor is shut off. The more frequently a brake pedal is actuated in a rolling vehicle, the more vacuum is lost. Once the pressure compensation with the ambient air is achieved in the vacuum system, the brake booster's effect ceases. Yet, it is expected that electrically powered vacuum pumps will appear in the future. Even today, electrically powered vacuum pumps are being used in hybrid vehicles in order to guarantee the maximum braking power even when using a pure electric drive.
Vacuum pump defects
Vacuum pump defects will immediately be noticed, for the brake pressure at the brake pedal rises significantly. Although the braking effect is not completely lost, it is severely impaired. Naturally, all other auxiliary units connected to the vacuum pump will also be affected if this component fails. Modern vehicles have a sensor that registers the failure of the vacuum system. You can read this in the vehicle's fault memory. Yet, before replacing a vacuum pump, all vacuum lines should be inspected for leaks. Oftentimes the issue is caused by a leak, which is easier and cheaper to repair than replacing the vacuum pump.
Repairing the vacuum pump
Vacuum pumps can't usually be repaired, only replaced. Most of them consist of a tightly closed system that can't be disassembled. Under certain circumstances, it is possible to clean it with brake cleaner. However, this only offers short-term temporary relief. Fortunately, the vacuum pump is usually very easily accessible and can be replaced with just a few hand movements.
Vacuum pump prices
Although the vacuum pump is an important and complex component, a replacement usually costs surprisingly little. Even highly stressed units, such as those used in large passenger car diesel engines, rarely cost more than 250 euro. Vacuum pumps for small and mid-sized cars usually cost around 50-100 euro. However, this only applies to the common, power-operated vacuum pump. Vacuum pumps with an electric motor are far more expensive, yet these components allow for removing the pump module from the electric motor and replacing it separately.