Attention: Those discs that have grooves, scuffs, are completely worn out or warped, must be replaced or machined.
Before measuring disc axial runout, make sure that the front wheel bearing runout is within the manufacturer's specification.
Raise and secure the vehicle on stands. When lifting only the front of the vehicle, apply the parking brake and block the rear wheels.
Remove the wheel.
Remove the brake caliper and fasten it to a wire outside the working area. Do not disconnect the brake hose, but do not let the caliper hang from the hose. For more details, see Replacement of brake discs.
If the disc is easily removed from the hub, install the bolts and tighten them a little more than by hand. Make sure that the tightening torque for all nuts is approximately the same.
Install a dial indicator with a magnetic or universal holder on the car body so that the indicator needle touches the side surface of the disc at a distance of about 13 mm from its outer edge.
Set the indicator to «zero». Rotate the dial one full turn and record the maximum axial runout reading. Compare the value obtained with the value indicated for your vehicle.
• If the amount of axial runout exceeds the limit, the disc may need to be reinstalled. If the disc comes off easily enough, remove it, clean the contact surfaces of the disc and hub, and reinstall the disc, but in a new position. Measure the runout again. If this time the runout is within specifications, then the problem is solved. If not, replace or grind the disc.
The thickness of the disc significantly affects its ability to withstand heat and provide adequate deceleration force. Each disc has a minimum thickness allowed by the manufacturer.
The marking indicating the minimum allowable thickness is indicated on the brake disc itself.
In this case, it is 19.8 mm.
This minimum thickness must not exceed the limits specified in the specifications. A disc that is thinner than necessary may crack during braking.
If at least some part of the disc is less than the minimum thickness, it must be replaced.
Thickness and change in thickness can be measured with a micrometer. All measurements must be taken at some distance from the edge of the disc, since the box has a shoulder. Take measurements at four points symmetrically located on the disc circumference, and write down the measurement results. Compare them with the minimum values given in the specifications. Disc thickness unevenness of more than 0.025 mm may cause brake pedal vibration and/or vibration at the front of the vehicle during braking. A disc that does not meet the specifications for thickness or thickness unevenness must be replaced.
The new disc has a smooth, flat surface that quickly changes during operation. Sometimes very thin concentric grooves appear and develop on the surface of the disc (similar to soundtracks on music records), which are formed as a result of exposure to dust and small solid particles that enter the disc from the brake linings. This slight roughness is quite normal, but if any of the grooves are so deep that a fingernail can catch on them, the disc should be replaced.
If tarnishing, discoloration of the metal, severe rust or even chipping appear, the disc should be replaced. If something is in doubt during inspection, replace the disc. The front brakes are a very important system and must be 100% efficient.
At the same time as the disc, the brake linings should be replaced, as their surface must be perfect. Since the brake pads are replaced as a set (on both wheels), respectively, both disks must be replaced, even if only one is damaged.