Brakes

Brakes

Both the 528i and the 540i come with the ASC/5 system as standard equipment.

The 528i/540i (E39) continues to use the "Black/White" hydraulic circuit layout. Aluminum components are also used in the brake system where possible to reduce the unsprung weight of the vehicle.

The brake lining thickness can be checked without wheel removal on all models except M5 (E39) using a similar depth type gauge.






The E39 brake calipers have a special notch integrated into the casting that allows a special tool (P/N 341 260) to be inserted to check the thickness of the brake pad material. This procedure can be done with the wheel on as shown.

Brake Booster Vacuum Supply






A 10" vacuum booster is used for the power assist. A new vacuum supply system is introduced on the 540i. This system will also be used on all M62 equipped vehicles (740i and 840Ci).

The system components include:

- Twin vacuum supply check valve
- Vacuum amplifier (venturi effect)
- Molded idle control valve air supply hose with "T" fitting.
- Various hoses and tubing.

Operation
The system is designed to provide an uninterrupted, consistent vacuum supply to the brake booster under all engine operating conditions. The system provides an alternate amplified vacuum supply for these conditions.

The manifold vacuum and ported vacuum from the idle control valve circuit are combined and amplified in the vacuum amplifier located at the front of the engine. The stronger vacuum source is provided by the check valve and to the booster.