Brake Rotor/Disc: Testing and Inspection

Each time the brakes are serviced the front and rear disc brake rotors should be checked for scoring, runout, parallelism and thickness.

Front and rear disc brake rotor scoring and runout may be checked with the front and rear disc brake rotors either on or off the vehicle. To check parallelism and thickness, the front or rear disc brake caliper must be removed.


Runout
1. Remove caliper and caliper bracket.

2. NOTE: Make sure all mating surfaces between the hub flange and the rotor are clean and free of rust or contaminants to prevent an erroneous reading.

Mount the rotor with all wheel nuts firmly tightened.
3. Make sure the axle wheel hub retainers are tight and the wheel bearings are not worn to eliminate all end play from the wheel hubs.
4. Mark a stud-to-rotor beginning index point.
5. Attach Rotunda Disc Rotor and Ball Joint Gauge 134-R0199 or equivalent to some part of the vehicle suspension so the stylus of the indicator touches the surface of the disc brake rotor approximately 25.4 mm (1 inch) from outer edge of the disc brake rotor.
6. Adjust the dial indicator to mid travel. Zero the scale on the dial indicator. Slowly turn the disc brake rotor one complete turn and note the high and low readings on the dial. The total between the high and low readings must not exceed the specified runout limit.

Rotor Runout Setup, Front:

Rear Rotor Runout:

7. NOTE: The gauge can remain mounted at the same location. Loosen the tension on the flexible gauge arm and move the dial indicator well away from the area and tighten while components are being removed or installed.

If the runout is not within specification, remove the rotor and measure the hub flange mounting face outside of the stud circle.
8. If the runout of the hub flange exceeds specification, install a new hub assembly and repeat flange face runout measurement. Reinstall the rotor and repeat the rotor runout measurement.
9. If the runout of the hub flange is within specification, reindex the rotor and repeat the measurement.
10. If the rotor still exceeds the specification, refinish or replace the rotor as required. Repeat the runout measurement and reindex the rotor if necessary.
11. Reinstall the caliper and caliper bracket.

Parallelism
Parallelism is the variation in the thickness of the disc brake rotor. If the two rubbing surfaces of the disc brake rotor are not parallel, the disc brake rotor may cause excessive brake pedal travel, a pulsating brake pedal, or noise.

Two methods can be used to check if the two faces of a disc brake rotor are parallel. A micrometer can be used to measure the disc brake rotor thickness at 12 points approximately 30 degrees apart and 25.4 mm (1 inch) from the outer edge of the disc brake rotor.

The other method is to measure the disc brake rotor on a precision lathe designed for machining disc brake rotors. Attach two dial indicators, one on each side of the disc brake rotor, so that the stylus of each indicator contacts the rubbing surface, directly opposite each other, approximately 9.5 mm (.38 inch) from the outer edge of the disc brake rotor.

Zero both indicators and rotate the disc brake rotor while watching both dials. If the total readings of both indicators exceed the specified limit for parallelism (0.0 10 mm/0.0004 inch), the disc brake rotor must be refinished or replaced.


Refinishing
Do not machine, cut, or true up new front disc brake rotor or rear disc brake rotor prior to installation on vehicle. Making a light cut on a new front disc brake rotor or rear disc brake rotor may cause excessive runout and result in brake shudder several thousand miles later. Clean oil film off a new front disc brake rotor and rear disc brake rotor with Metal Brake Parts Cleaner F5AZ-2C410-AA or equivalent.

Use Rotunda Hub Mount Brake Lathe 201-00001 or equivalent to refinish the disc brake rotor.

1. Follow the on-vehicle brake lathe manufacturer's instructions on machining procedures.

Replace the disc brake rotor when the overall thickness is at or below the specified minimum thickness shown on the disc brake rotor.


Service Limits

CAUTION: Never refinish a disc brake rotor to the minimum wear or discard thickness.

Measure the thickness of the disc brake rotor to determine if it is within the specification. Disc brake rotor minimum (discard) thickness is cast in the disc brake rotor. Disc brake rotors have a minimum thickness dimension (minimum wear thickness or discard thickness). This is not the refinishing dimension.