Rebuilt / Remanufactured power brake booster master vacuum unit for a 1973-1978 Datsun 240Z, 260Z, or 280Z. For coupe models only. An excessively firm brake pedal is a common sign of a bad Brake Master Vac unit. These units usually fail when internal diaphragm is torn and/or deteriorates over time. We also recommend checking your brake check valve and master vac hoses, as they can contribute to braking issues as well.