[ecomodded]

I have found some good info on brake boosters today, it seems some newer cars use hydraulic pressure generated by the power steering pump rather than engine vacuum to provide the power assistance.
Most of the gasoline cars brake boosters use the engine vacuum with the assistance of a rubber hose that comes from the intake manifold.
On diesels, the 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.
The pump is driven mechanically through either a gear drive or a port on the rear of the mounting flange.