Brake Rotor Assembled Lateral Runout (LRO) Measurement

Tools Required

• J 39544-KIT  Torque-Limiting Socket Set, or equivalent. See Special Tools and Equipment .
• J 41013  Rotor Resurfacing Kit. See Special Tools and Equipment .
• J 42450-A  Wheel Hub Resurfacing Kit. See Special Tools and Equipment .
• J 45101  Hub and Wheel Runout Gage. See Special Tools and Equipment .
• J 45101-100  Conical Brake Rotor Washers. See Special Tools and Equipment .

1. Matchmark the position of the brake rotor to the wheel studs if this has not been done already.
IMPORTANT: Whenever the brake rotor has been separated from the hub/axle flange, any rust or contaminants should be cleaned from the hub/axle flange and the brake rotor mating surfaces. Failure to do this may result in excessive assembled lateral runout (LRO) of the brake rotor, which could lead to brake pulsation.
2. Inspect the mating surface of the hub/axle flange and the brake rotor to ensure that there are no foreign particles, corrosion, rust, or debris remaining. If the wheel hub/axle flange and/or if the brake rotor mating surfaces exhibit these conditions, perform the following steps:
   1. Remove the brake rotor from the vehicle. Refer to Brake Rotor Replacement - Front  and/or Brake Rotor Replacement - Rear .
   2. Using the J 42450-A  , thoroughly clean any rust or corrosion from the mating surface of the hub/axle flange. See Special Tools and Equipment .
   3. Using the J 41013  , thoroughly clean any rust or corrosion from the mating surface of the brake rotor. See Special Tools and Equipment .
   4. Clean the friction surfaces of the brake rotor with denatured alcohol, or an equivalent approved brake cleaner.
3. Install the rotor to the hub/axle flange using the matchmark made prior to removal.
Fig 1: Identifying J 45101-100 & Lug Nut
Courtesy of GENERAL MOTORS CORP.
4. Hold the rotor firmly in place against the hub/axle flange and install one of the J 45101-100  (1), and one lug nut (2) onto the upper-most wheel stud. See Special Tools and Equipment .
5. Continue to hold the rotor secure and tighten the lug nut firmly by hand.
Fig 2: Installing All J 45101-100s & Lug Nuts
Courtesy of GENERAL MOTORS CORP.
6. Install the remaining J 45101-100  and lug nuts onto the wheel studs and tighten the nuts firmly by hand in a star-pattern. See Special Tools and Equipment .
7. Using the J 39544-KIT  , or equivalent, tighten the lug nuts in a star-pattern to specification, in order to properly secure the rotor. See Special Tools and Equipment . Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
8. If the brake rotor has been REFINISHED or REPLACED with a new rotor, proceed to step 14.
9. If the brake rotor meets the following criteria, proceed to step 10.
   • The rotor is within specifications and is being REUSED
   • The rotor has NOT been refinished
   • The rotor does NOT exhibit thickness variation exceeding the maximum allowable level
Fig 3: Mounting Dial Indicator To Measure Lateral Runout
Courtesy of GENERAL MOTORS CORP.
10. Mount a dial indicator, J 45101  , or equivalent, to the steering knuckle and position the indicator button so it contacts the brake rotor friction surface at a 90 degree angle, approximately 13 mm (0. See Special Tools and Equipment .5 in) from the outer edge of the rotor.
11. Measure and record the assembled LRO of the brake rotor.
    1. Rotate the rotor until the lowest reading is displayed on the indicator dial, then set the dial to zero.
    2. Rotate the rotor until the highest reading is displayed on the dial.
    3. Mark the location of the high spot relative to the nearest wheel stud, or studs.
    4. Measure and record the amount of LRO.
12. Compare the brake rotor assembled LRO to the following specification:

    Specification: 

    • Front brake rotor maximum allowable assembled lateral runout: 0.05 mm (0.002 in)
    • Rear brake rotor maximum allowable assembled lateral runout: 0.05 mm (0.002 in)

13. If the brake rotor assembled LRO is within specifications, proceed to step 18.

    If the brake rotor assembled LRO exceeds the specification, refinish the rotor to ensure true parallelism, refer to Brake Rotor Refinishing . After refinishing the rotor, proceed to step 14.

Fig 4: Mounting Dial Indicator To Measure Lateral Runout
Courtesy of GENERAL MOTORS CORP.
14. Mount a dial indicator, J 45101  , or equivalent, to the steering knuckle and position the indicator button so it contacts the brake rotor friction surface at a 90 degree angle, approximately 13 mm (0. See Special Tools and Equipment .5 in) from the outer edge of the rotor.
15. Measure and record the assembled LRO of the brake rotor.
    1. Rotate the rotor until the lowest reading is displayed on the indicator dial, then set the dial to zero.
    2. Rotate the rotor until the highest reading is displayed on the dial.
    3. Mark the location of the high spot relative to the nearest wheel stud, or studs.
    4. Measure and record the amount of LRO.
16. Compare the brake rotor assembled LRO to the following specification:

    Specification: 

    • Front brake rotor maximum allowable assembled lateral runout: 0.05 mm (0.002 in)
    • Rear brake rotor maximum allowable assembled lateral runout: 0.05 mm (0.002 in)

17. If the brake rotor assembled LRO measurement exceeds the specification, bring the LRO to within specifications. Refer to Brake Rotor Assembled Lateral Runout (LRO) Correction .
18. If the brake rotor assembled LRO measurement is within specification, install the brake caliper and depress the brake pedal several times to secure the rotor in place before removing the J 45101-100  and the lug nuts. See Special Tools and Equipment .