BMW 7 Series: Checking Brake Discs

Necessary preliminary tasks

• Remove WHEELS.

Checking thickness difference:

• Measure thickness difference within brake surfaces at 8 point (spread over the circumference) with a micrometer gauge
• Compare measurement result with setpoint value.

Fig. 6: Measuring Thickness Difference Within Brake Surfaces Using Micrometer Gauge

Check minimum brake disc thickness:

• Position special tool 34 1 280 at three measuring points in area (1) and measure.
• Compare measurement result and lowest value with setpoint value.

Fig. 7: Checking Brake Disc Thickness

CHECKING THICKNESS OF BRAKE PAD

Notes

NOTE: The thickness of the outer brake pads can be determined without removing the wheels.

If necessary, move car until opening for brake pad wear indicator (brake pad) can be seen through rim styling.

Insert special tool 34 1 260 rim into opening for brake pad wear indicator.

Press special tool onto brake pad. Slide ring (1) in direction of arrow up to stop and read off measured value.

NOTE:

1. Brake disc
2. Brake pad with backplate

Safe limit for lining wear, front brake.

Safe limit for lining wear, rear brake.

Fig. 8: Inserting Special Tool (34 1 260) Rim Into Opening For Brake Pad Wear Indicator

General Information

The brake system is one of the most important safety systems on any vehicle. It is therefore essential to act with utmost care when performing repair work on the brake system and to follow the instructions below.

General

• Ensure cleanliness and use only fluff-free cleaning cloths.
• Wash away or vacuum up brake dust, do not clear it away using compressed air. This dust is a health hazard.
• Do not under any circumstances allow any oil or grease to get into the brake system. This would result in a complete malfunction of the brake system.
• When cleaning brake components with brake cleaner, make sure that no brake cleaner gets into the brake system.
• Even the most minute traces of brake cleaner must be avoided.

Brake fluid

• Replace brake fluid at least every two years.
• Important: Never reuse drained off brake fluid.
• Use only BMW-approved brake fluid. See BRAKE SYSTEM - OPERATING FLUIDS.
• Dispose of brake fluid in approved appliances only, refer to BMW Service Workshop Equipment Planning documentation.
• Do not allow brake fluid to drain into drain pipes, into the outside environment or into unsuitable facilities. This would create the risk of groundwater contamination since brake fluid is classed as a fluid that is hazardous to water.
• Do not allow brake fluid to come into contact with paintwork as this will destroy the paint.
• Brake fluid must not be allowed to remain on bare skin too long in order to avoid skin problems. Wash skin coated with brake fluid with water and soap.
• If brake fluid makes contact with eyes, immediately flush with large quantity of clean water and visit eye doctor.

Wheel brakes

• Brake pads:
  Brake pads must be replaced when the remaining brake pad thickness is reached.

  Brake pads must always be replaced on both sides of any axle.

  The friction surfaces of the brake pads must not come into contact with oil or grease. The brake pads must be replaced if they are dirt contamination by such substances.

  In the case of rotation-dependent brake pads, make sure the arrow marking points in the direction of rotation of the brake disc for when the vehicle is moving forward. Brake pads with left/right markings must be fitted on the relevant side of the vehicle.

  One-sided angled areas on the brake pads must be located on the disc contact side of the brake caliper for when the vehicle is moving forward.

• Brake discs:
  Brake discs must not be scored or cracked. Furthermore, minimum brake disc thickness disc runout, parallelism and surface roughness of the friction surfaces must not exceed or drop below the permitted values.

  Always strip preservative off new parts before installation. With the rear brake discs, also strip preservative off brake drum on parking brake.

• Always strip preservative off new parts before installation.
• Brake calipers:
  Only approved glycol-based assembly pastes may be used for repairs on brake calipers.

  All moving components on the brake caliper must move freely: note grease specifications.

  Use only BMW-approved lubricants to grease the brake caliper guides.

Brake lines, brake hoses

• Brake lines and brake hoses must be correctly routed and must not abut with body or components in a way which would cause chafing.
• To prevent damage, release and tighten brake line couplings with a special brake line wrench only.
• The system must be bled each time any brake lines have been detached.
• All connection points must be checked for leaks.
• Only tighten down brake hoses on the front axle when wheels are in straight-ahead position.
• Close off open connections of brake lines and individual components to prevent dirt from getting into the brake system.
• Observe tightening torque when tightening down brake line couplings.

Traction control system

The traction control system is basically maintenance-free. However, be sure to adhere to the following:

• When carrying out welding work with electric welding equipment, be sure to disconnect the plug from the electronic control unit (ignition turned off).
• During painting work, the control unit may be subjected for brief periods to max. 95ºC and for long periods (approx. 2 hours) to max. 85ºC.
• Terminals must be completely tight on end poles of battery.
• The brake lines on the hydraulic unit must not be mixed up; if necessary, mark them prior to disassembly.
• On completion of repair work, carry out mix-up test with the DIS diagnosis system.

GENERAL INFORMATION ON BRAKING IN NEW BRAKE DISCS/BRAKE PADS

IMPORTANT: After completing work:

• Carry out function check on brake test stand to ensure that the brakes complies with legal requirements.
• Carry out test braking while driving at low speed; the effectiveness of the brakes may be reduced during the initial braking operations.
• Exaggerated drastic and continuous braking operations for faster braking in are not permitted.
• Advise the customer not to perform any wilful drastic braking in the first 200 km after brake replacement.
• Attach mirror tag to interior rearview mirror.

PARKING BRAKE FUNCTION CHECK

• Connect BMW diagnosis system.
• Carry out vehicle test
• Call up "Workshop braking-in" service function.
• Start braking-in program.
• (Parking brake indicator lamp in instrument cluster flashes at low frequency)
• Drive vehicle onto brake analyzer and pull parking brake button once.
• Parking brake is applied at approx. 15 km/h with reduced force.
• (Parking brake indicator lamp in instrument cluster flashes at high frequency)
• Braking-in procedure takes 3 minutes.
• Braking-in procedure can be terminated by pressing the parking brake button.
• Delete fault memory.

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