Note: Before you begin, please read the warning at the beginning of this manual regarding the dangers and hazards of asbestos dust paragraph 4.
Inspection
Note: If either disc requires replacement, replace both discs at the same time. This will ensure consistent and consistent braking. New brake pads should also be installed.
1. Fully apply the parking brake. Raise the front of the vehicle and support it securely (see "Lifting and installing the car on supports"). Remove the corresponding front wheel.
2. Rotate the brake disc slowly so that both surfaces of the disc can be checked. If you want to get better access to the inner surface, remove the brake pads. Light scratches in the contact area with the brake pads are normal, but if serious scratches are found, the disc should be replaced.
3. There is nothing unusual about a strip of rust or dust from the brake pads around the perimeter of the disc; if necessary, these traces can be cleaned up. However, if due to increased wear a certain step has formed in the contact area with the brake pads, the thickness of the disc should be measured using a micrometer (figure 6.3). Measurements should be taken at several locations around the disc circumference, on the inner and outer diameters of the pad contact area. If the disc thickness at any point reaches the minimum specified value or is less, the disc should be replaced.
Figure 6.3. Measure the disc thickness with a micrometer
4. If you think the disc is warped, you can check its runout by following the steps below. Either use a dial indicator, which should be attached to any convenient fixed point, and slowly rotate the disc relative to it, or use a feeler gauge to measure the gap between the disc and a fixed element such as a brake caliper support bracket at several places around the circumference of the disc. If the results obtained correspond to or exceed the limit value, the disc has increased deformation and should be replaced. However, first it is worth checking the condition of the hub bearing (see chapter 1A or 1B and/or 10). Also try removing the disc and reinstalling it, after rotating it 180° relative to the hub. If the runout is still excessive, the disc should be replaced.
Figure 6.4. Checking the disc runout using a dial indicator
5. Check the disc for cracks (especially in the area of the holes for the wheel mounting bolts) and any other signs of wear or damage. Replace it if necessary.
Removal
6. Remove the brake pads as described in paragraph 4.
7. Remove the two bolts securing the brake caliper support bracket to the steering knuckle (figure 6.7). Remove the support bracket together with the caliper from the disc and steering knuckle and tie the assembly to the front spring to prevent deformation of the brake hose.
Figure 6.7. Front caliper support bracket mounting bolts (marked with arrows)
8. Use chalk or paint to mark the relative positions of the disc and hub. Then unscrew all the screws securing the disc to the hub and remove the disc (figure 6.8, a, b). If the disc does not come off, lightly tap the back of the disc with a plastic hammer to loosen it from the hub.
Figure 6.8, a. Remove two screws...
Figure 6.8, b....and remove the front brake disc
Installation
9. Installation is carried out in the reverse order of removal, taking into account the following points:
- a) Make sure the mating surfaces of the disc and hub are clean and flat.
- b) When installing the disc on the hub, align the marks made during removal and securely tighten the disc mounting screws.
- c) If a new disc has been installed, remove the preservative coating from the disc using a suitable solvent before installing the caliper.
- d) Apply a suitable thread locking compound to the threads of the caliper support bracket mounting bolts and tighten the bolts to the specified torque.
- d) Install the wheel, lower the vehicle and tighten the wheel bolts to the specified torque. Finally, depress the brake pedal several times to restore normal (without vacuum amplification effect) pedal pressure.