Brake Rotor Assembled Lateral Runout (LRO) Measurement

Tools Required

• J 41013  Rotor Resurfacing Kit. See Special Tools .
• J 42450-A  Wheel Hub Resurfacing Kit. See Special Tools .
• J 45101  Hub and Wheel Runout Gage. See Special Tools .
• J 45101-100  Conical Brake Rotor Washers. See Special Tools .

1. Measure the brake rotor thickness. Refer to Brake Rotor Thickness Measurement .
2. Measure the brake rotor thickness variation. Refer to Brake Rotor Thickness Variation Measurement .
Fig 1: View of Brake Rotor, Wheel Stud, and Hub
Courtesy of GENERAL MOTORS CORP.
IMPORTANT: The brake rotor is indexed to the hub during production in order to minimize LRO.
3. If match marks are not evident, use paint in order to mark the relative position of the following components:
   • The brake rotor (1)
   • A wheel stud (2)
   • The hub (3)
4. Remove the brake rotor from the vehicle. Refer to Brake Rotor Replacement - Front  or to Brake Rotor Replacement - Rear  as applicable.
IMPORTANT: Rust or contaminants on the hub flange or on the brake rotor mating surfaces may cause excessive LRO of the brake rotor, which could lead to brake pulsation.
5. Inspect the mating surface of the hub flange and the brake rotor. If rust or foreign particles are on the hub flange or the brake rotor mating surfaces, perform the following steps:
   1. Use the J 42450-A  , or equivalent, in order to thoroughly clean any rust or contaminants from the mating surface of the hub flange. See Special Tools .
   2. Use the J 41013  , or equivalent, in order to thoroughly clean any rust or contaminants from the mating surface of the brake rotor. See Special Tools .
   3. Clean the friction surfaces of the brake rotor with denatured alcohol or an equivalent brake cleaner.
6. Align the paint marks and install the rotor to the hub flange.
Fig 2: Identifying J 45101-100 & Lug Nut
Courtesy of GENERAL MOTORS CORP.
7. Hold the rotor firmly in place against the hub flange. Install one of the J 45101-100  and one wheel nut (2) onto the upper-most wheel stud. See Special Tools .
8. Continue to hold the rotor secure and tighten the wheel nut firmly by hand.
Fig 3: Installing All J 45101-100s & Lug Nuts
Courtesy of GENERAL MOTORS CORP.
9. Install the remaining J 45101-100  and the wheel nuts onto the wheel studs and tighten the nuts firmly by hand in a star pattern. See Special Tools .
NOTE: Refer to Fastener Notice in Cautions and Notices.
10. Tighten the wheel nuts in a star pattern in order to retain the rotor to the hub. Refer to Fastener Tightening Specifications in Tires and Wheels.
Fig 4: Mounting Dial Indicator To Measure Lateral Runout
Courtesy of GENERAL MOTORS CORP.
11. Perform the following steps in order to measure and record the assembled LRO of the brake rotor.
    1. Install the J 45101  , or equivalent. See Special Tools . Position the indicator button so it contacts the brake rotor friction surface 10 mm (0.39 in) from the outer edge of the rotor.
    2. Verify the indicator is at a 90 degree angle to the brake rotor.
    3. Rotate the rotor until the indicator dial displays the lowest reading.
    4. Set the dial to zero.
    5. Rotate the rotor until the indicator dial displays the highest reading.
    6. Mark the location of the high spot relative to the nearest wheel stud or studs.
    7. Measure and record the amount of LRO.
12. Compare the LRO to the following specification:

    Specification: 

    • Front brake rotor maximum allowable LRO: 0.05 mm (0.002 in)
    • Rear brake rotor maximum allowable LRO: 0.08 mm (0.003 in)

13. If the LRO measurement is within the specification, complete the following steps:
    1. Remove the J 45101  . See Special Tools .
    2. Install the brake caliper and the brake pads. Refer to Brake Pads Replacement - Front  or to Brake Pads Replacement - Rear  as applicable.
    3. With the engine OFF, gradually apply and release the brake pedal several times in order to position the caliper pistons.
    4. Remove the wheel nuts.
    5. Remove the J 45101-100  . See Special Tools .
    6. Install the tire and wheel assemblies. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
14. If the LRO measurement EXCEEDS the specification and you REFINISHED or REPLACED the rotor, adjust the LRO. Refer to Brake Rotor Assembled Lateral Runout (LRO) Correction .
15. If the LRO measurement EXCEEDS the specification and you DID NOT refinish or replace the rotor, refinish the rotor in order to attain true parallelism. Refer to Brake Rotor Refinishing .
16. Measure the LRO in order to verify the rotor is within the specification.