Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Mechanical - Hydraulic: Disc: Description
All BMW E32 models are equipped with power-assisted four-wheel disc brakes with integral anti-lock brakes (ABS). A brake booster power-assists a dual-circuit master cylinder. Two types of brake assist systems are used depending on model and model year. Hydraulic boost systems use fluid from the power steering pump. A heavy duty dual diaphragm vacuum booster is used on 740i/iL models. See BRAKE BOOSTER SYSTEMS table.
The pressure controlled power flow regulator taps a slight delivery flow from the operating circuit of power steering for the hydraulic brake booster, and charges the hydraulic reservoir in a pressure range without impairing the function of power steering. The hydraulic oil volume stored under pressure is available for the booster to support the operating force and is called by operating the brake master cylinder. If the power steering pump fails, sufficient reserve pressure will be stored in the hydraulic reservoir to be able to execute several braking actions with full brake boosting support. After consumption of this reserve pressure, the brakes can still be applied, but without boost and therefore with considerably more force on the brake pedal.
A dual-chamber master cylinder pressurizes 2 separate hydraulic circuits. Front circuit actuates left front and right rear brakes, and rear circuit actuates right front and left rear brakes. All models are equipped with single piston front and rear calipers.
Front and rear rotors are mounted to wheel hubs. Front rotors are vented and rear rotors are vented or solid. Left front and right rear brake pads contain wear sensors which will illuminate light in instrument panel when pads need replacement. Cable actuated parking brake is a dual-drum system integrated with rear brake rotors.
Automatic Stability Control (ASC) or Automatic Stability Control + Traction (ASC+T) system is equipped on 1990 and later vehicles. Check for an ASC switch mounted in center console. In addition to the normal ABS function, the traction control system controls engine throttle and timing to reduce engine torque to help maintain vehicle stability. On later models equipped with ASC+T, an additional hydraulic pump is used to actuate rear brakes when rear drive wheels are spinning faster than the front wheels. ASC+T hydraulic control pump is mounted next to left front strut tower in engine compartment.
The parking brake is a dual drum system integrated into the rear wheel brake rotors. Parking brake shoe replacement is not normally required, but periodic adjustment of the shoes may be necessary from time to time to compensate for wear. The parking brake should also be adjusted any time the cable, the rear brake discs or the parking brake shoes are replaced.
| Application | Production To 3/88 | Production After 3/88 |
|---|---|---|
| 735i/iL | Hydraulic Booster | Vacuum Booster |
| 740i/iL | Vacuum Booster | Vacuum Booster |
| 750iL | Hydraulic Booster | Hydraulic Booster |
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.