BMW part number 34331156579 is a Brake Booster Non-Return Check Valve. It is easily recognizable because it features a 90-degree right-angle white plastic elbow on one side that pushes directly into the rubber sealing grommet on the face of the brake booster capsule, while the other side connects to the intake manifold vacuum hose.
1. The Booster Inlet Side (Push-In Elbow) - Outer Diameter (OD): 14 mm....This side features a smooth, unbarbed plastic nipple tip. It is designed to slide directly inside the heavy rubber sealing grommet embedded in the sheet-metal wall of the power brake booster servo canister.
2. The Engine Outlet Side (Hose Barb) - Outer Diameter (OD): 12 mm....This side features a straight, ridged barb. It slides inside the primary flexible vacuum line running to the engine intake manifold and is clamped securely to prevent vacuum leakage.
(Note: The actual internal passage bore diameter through the center core of the plastic valve itself measures roughly 8 mm to optimize the airflow rate pulled by the engine's intake stroke).
It fits the following US years, models, and specific engine options:
BMW 3 Series (E30 Chassis)
- 1984–1985 BMW 318i (1.8L Inline-4, M10 engine)
- 1991–1992 BMW 318i / 318is / 318i Convertible (1.8L Inline-4, M42 engine)
- 1984–1987 BMW 325e / 325es (2.7L Inline-6, M20 "Eta" engine)
- 1987–1991 BMW 325i / 325is (2.5L Inline-6, M20 engine — Coupe and Sedan)
- 1987–1993 BMW 325i Convertible (2.5L Inline-6, M20 engine)
BMW 5 Series (E28 Chassis)
- 1987–1988 BMW 528e (2.7L Inline-6, M20 "Super Eta" engine)
