If there are burrs, deep scratches and other defects on the working surface of the disc that increase pad wear and reduce braking efficiency, as well as in the case of increased lateral runout of the disc that causes vibrations during braking, replace the disc. In specialized workshops, such a disc can be turned and ground on both sides to the same depth, but after processing, the thickness of the disc must not be less than the minimum permissible (23.2 mm).
The minimum permissible thickness of the brake disc of the front brake mechanism when worn is 23.0 mm. If the thickness of one of the discs is less than the specified value, replace both discs. When replacing the brake discs, be sure to replace the brake pads with a new set.
1. Remove the wheel from the side of the disc being replaced.
2. Remove the caliper (see Replacing the front wheel brake caliper), without disconnecting the brake hose, and secure it with wire to the front suspension spring. Do not allow the hose to twist or stretch.
Note: To be able to secure the caliper with wire to the front suspension spring, remove the brake hose retainer from the bracket slot on the shock absorber strut before removing the caliper.
3. Remove the guide from the steering knuckle (see Replacing the front wheel brake caliper).
4. Unscrew the bolt securing the disc to the hub…
5. ...and remove the disk.
6. Similarly, remove the brake disc of the brake mechanism of the other front wheel.
7. Install the parts in the reverse order of removal.
Note. The Opel Astra J can be equipped with wheels of two sizes: 155 and 166 inches. Due to this, some brake mechanism parts installed on different vehicle configurations have different sizes. In particular, the diameters of the brake discs of the front wheel brake mechanisms are 276 and 300 mm for installation with wheels of 15 and 16 inches, respectively. Take this into account when purchasing new brake discs.
Note: Before installing the disc, thoroughly clean the mating surfaces of the hub and disc from rust and scale, since even the smallest particle clamped between the mating surfaces will cause disc beating and vibrations during braking.
Note: If you are installing the same disc, use a file to remove the ridges on the working surfaces of the disc that have formed on both sides as a result of disc wear.
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