Brake Rotor/Disc: Testing and Inspection

Inspection
In the manufacturing of the brake rotor, all the tolerances regarding surface finish, parallelism and lateral runout are held very closely. Maintaining these tolerances provides the surface necessary to assure smooth brake operation.

Lateral Runout
Lateral runout is the movement of the rotor from side to side as it rotates on the spindle. This could also be referred to as "rotor wobble".
This movement causes the piston to be knocked back into its bore. This results in additional pedal travel and a vibration during braking.

Checking Lateral Runout
1. Adjust the wheel bearing correctly.

Checking Lateral Runout:

2. Attach the dial indicator accordingly so that the stem contacts the rotor surface to approximately 29 mm (1.14 inch) from the rotor edge.
3. Rotate the rotor one complete turn and inspect for signs of lateral runout. Lateral runout should not exceed 0.13 mm (0.005 inch).
Maximum runout: 0.13 mm (0.005 inch)

Parallelism

Measuring Thickness Of Rotor:

Parallelism is the measurement of thickness of the rotor at four or more points around the circumference of the rotor. All measurement must be made at 29 mm (1.14 inch) from the edge of the rotor.
The rotor thickness must not vary more than 0.010 mm (0.0004 inch) from point to point.
Maximum runout: 0.010 mm (0.0004 inch)

Replacing Brake Rotors
When installing new brake rotors, do not refinish the surfaces. These parts are at the correct level of surface finish.

Refinishing Brake Rotors





Accurate control of the rotor tolerances is necessary for proper performance of the disc brakes. Machining of the rotor should be done only with precision equipment. All brake rotors have a minimum thickness dimension cast into them. This dimension is the minimum wear dimension and not a refinish dimension.
The minimum wear dimension is 24.60 mm (0.969 inch).
The minimum refinish dimension is 24.97 mm (0.983 inch).
When refinishing rotors, always use sharp cutting tools or bits. Dull or worn tools leave a poor surface finish which will affect initial braking performance. Vibration dampening attachments should always be used when refinishing braking surfaces. These attachments eliminate tool chatter and will result in better surface finish.
After refinishing, replace any rotor that does not meet the minimum thickness of 24.97 mm (0.983 inch). Do not use a brake rotor that exceeds the manufacturers specifications.
Minimum wear dimension: 24.60 mm (0.969 inch)
Refinish dimension: 24.97 mm (0.983 inch)