Diesel Vacuum Pump

The diesel vacuum pump is an essential component for power brakes in diesel engine vehicles. By extracting air from the brake booster, it helps reduce the effort required to depress the brake pedal. Some pumps use a vane and rotor mechanism to create suction pressure, while others use a rubber diaphragm and plunger rod. Since both pump types operate continuously while the engine is running, they will eventually wear out and need to be replaced. Changing a diesel vacuum pump is a simple task that can be done by most people with a spanner set or an adjustable wrench.

Most drivers do not have the luxury of using a braking system powered by pressurized air or electric motor. The system used in most vehicles has brakes which are operated by hydraulic pressure, created when the brake pedal is depressed. A significant force needs to be applied to the pedal to build up this pressure, which making driving in busy traffic exhausting work because of frequent stopping. To reduce this effort, a component called a brake booster is installed in most vehicles.

The brake booster is a drum-shaped component which has two internal sections that are separated by a rubber diaphragm. When the brakes are not being used, both sections are kept at low pressure by suction provided by either the engine or a pump. When the brake pedal is depressed, a valve opens that allows air into the rear section of the booster. This extra pressure helps push the master brake cylinder piston forward and reduces the effort required to operate the brakes. When the brake pedal is released, the valve closes and air inside the rear section is removed through the vacuum hose.

A diesel engine does not create enough suction pressure by itself for the brake booster to function. Instead, engine power is used to drive a diesel vacuum pump to create the required pressure. A gasoline engine that uses a carburettor with butterfly valves is capable of providing enough suction pressure and does not require a pump. However, a gasoline engine that uses a fuel injection system instead of a carburettor does not create enough pressure and also needs a vacuum pump.

The diesel vacuum pump is a small component that weights around two pounds. The mounting flange and cover are made from diecast aluminum or steel. They are sealed together with a gasket and several bolts to form an airtight unit. The top of the pump is disc-shaped and measures several inches in diameter. There is a large air inlet for connecting the vacuum hose from the brake booster, and an exhaust port on the rear of the flange. A small oil inlet may also be present for adding engine oil to the pump. The pump is driven mechanically through either a gear drive or a port on the rear of the mounting flange.

An unusual increase in the force required to operate the brake pedal may indicate that the diesel vacuum pump has developed a fault. To test if the pump is still generating suction pressure, remove the end of the vacuum hose from the pump and start the engine. Place a thumb or flat object against the inlet valve of the pump and check if there is sufficient suction. If the pump is not the problem, there may be a leak in the vacuum hose or brake booster, or the master brake cylinder may even need to be replaced.

A new diesel vacuum pump can be purchased from stores that sell aftermarket car parts. New pumps are expensive and can cost several hundred dollars, but rebuild kits for some pumps are also available which are much less expensive. These kits include a new diaphragm and seals, as these are the parts that are most likely to fail. Rebuilding a pump can take some time and this should be considered when deciding whether to repair an old pump or buy a new one.

There Is 1 Response So Far. »

  1. Who can rebuild a vacuum pump. I live in pa. I have 2005 jeep liberty sport diesel. I am pretty sure the vacuum pump is leaking, as my pedal keeps fading to the floor.

    The new pump costs 350 dollars. A rebuild should be a less.