Front Brake Disc — Checking, Removing and Installing (BMW 3 Series E46)

Note 1: Please read the note at the beginning before you begin paragraph 4 about the dangers of asbestos dust.

Note 2: If one of the discs needs to be replaced, replace BOTH discs at the same time to ensure even and consistent braking. Replace the brake pads as well.

Examination

1. Apply the parking brake, then raise the front of the vehicle and support it on stands (see "Lifting and installing the car on supports"). Remove the corresponding front wheel.

2. Slowly turn the disc and inspect its surfaces on both sides. To better examine the inner surface, remove the brake pads (see paragraph 4). Small scratches are allowed on the surfaces of the disc that contact the pads. If there are deep scratches, burrs, or cracks, the disc must be replaced.

3. The periphery of the disc may have a border of rust and dust from wear of the pads. If necessary, all this can be scraped off. If such a border is formed due to excessive wear of the disc by the pad, the thickness of the disc must be measured with a micrometer (Fig. 6.3). Measure the thickness of the disc in several places along the inner and outer sliding radius of the pad. If in one of the places the thickness of the disc is at the limit (regulated by the "Technical Data" or below it), the disc must be replaced.



4. If you are not sure about the flatness of the disc, check the end runout. Measure the disc runout with a dial indicator attached to some fixed part, slowly turning the disc. Alternatively, measure the gap between the disc and some fixed part, such as the caliper support bracket, using flat feeler gauges. If the disc runout is at the limit (regulated Technical data or higher), then the disc most likely requires replacement, although first you need to make sure that the hub bearing support is in good condition (see chapter 10). If there is excessive runout, the disc must be replaced.



5. Inspect the disc for cracks, especially in the area of the wheel bolt holes, and for wear or damage. Replace the disc if necessary.

Removal

6. Remove the two bolts securing the caliper support bracket to the steering knuckle. Then remove the caliper. Use wire or twine to tie the caliper to the front suspension strut, being careful not to pull on the brake hose.

7. Mark the position of the disc relative to the hub, then unscrew the screw securing the disc to the hub and remove the disc (fig. 6.7, a, b). If the disc does not come off, tap it from the back with a plastic hammer.

Installation

8. Installation is performed in the reverse order of removal. When assembling, pay attention to the following.

• a) Clean the mating surfaces of the disc and hub from dirt.
• b) Align the marks made before removal, then screw in and tighten the disc mounting screw to the required torque.
• c) Before installing a new disc, clean the disc from the preservative with a suitable solvent.
• d) Place the caliper on the disc. Make sure that the pads are in the correct position relative to the disc. Tighten the caliper mounting bolts to the specified torque.
• d) Install the wheels, lower the car to the ground and tighten the wheel mounting bolts to the required torque. When finished, press the brake pedal several times to ensure that the pads fit the disc.