To inspect the brake disc, first apply the handbrake, loosen the relevant wheel nuts, jack up the front of the car, and support it on axle stands before removing the front wheel. Next, detach the front brake caliper from the disc without disconnecting the flexible hose, supporting the caliper on an axle stand or suspending it with wire to avoid straining the hose. Temporarily refit two wheel nuts to diagonally-opposite studs with the flat sides against the disc and tighten them progressively to hold the disc firmly. Scrape any corrosion from the disc, rotate it, and examine for deep scoring, grooving, or cracks, measuring the thickness in several places with a micrometer, ensuring it meets the minimum thickness stamped on the hub. Light wear is normal, but excessive wear requires removal for regrinding or replacement, maintaining the minimum thickness if regrinding is done. Check the disc run-out using a dial gauge or flat metal block and feeler gauges, ensuring it does not exceed the specified limit by fixing the measuring equipment and rotating the disc to note variations. If the run-out is excessive, measure the disc thickness at eight positions marked 45° apart, and if the variation exceeds the specified amount, the disc should be replaced. The hub face run-out can also be checked by removing the disc, fixing the measuring equipment, and rotating the hub to ensure the run-out is within limits; excessive run-out may require hub bearing replacement before rechecking the disc run-out. For removal, with the wheel and caliper off, take out the temporarily refitted wheel nuts, mark the disc in relation to the hub if it will be refitted, and remove the washer or retaining clip(s) before withdrawing the disc over the wheel studs. When refitting, ensure the disc and hub mating surfaces are clean, locate the disc on the wheel studs aligning any previously made marks if reusing the original disc, then reattach the washer or retaining clip(s) as applicable, followed by the brake caliper and carrier bracket. Finally, reattach the wheel, lower the car, tighten the wheel nuts to the specified torque, and test the brakes carefully before returning the car to normal service.
