Checking Rotor For Thickness & Runout
NOTE:
The procedure for checking rotor runout and thickness is same for front and rear rotor. If there is a specification difference between front and rear rotor it will be designated as such in specifications of following procedure.
On-vehicle rotor runout is combination of individual runout of hub face and runout of rotor. (The hub and rotor runout readings are separable). To measure runout on vehicle use following procedure.
- Remove tire and wheel from hub. Reinstall wheel mounting nuts. Tightening rotor to hub using wheel mounting nuts. Tighten wheel mounting nuts to specified torque of 135 N.m (100 ft. lbs.). Remove disc brake caliper from caliper adapter. Thickness variation measurements of rotor should be made in conjunction with lateral runout measurements. Measure thickness of rotor at 12 circumferentially equal points with a micrometer at a radius approximately 25.4 mm (1") from outer edge of rotor, see Figure . If thickness measurements vary by more than .013 mm (.0005"), rotor should be removed and resurfaced, or a new rotor installed. If cracks or burned spots are evident, rotor must be replaced. Light scoring and/or wear is acceptable. If heavy scoring or warping is evident, rotor must be refinished or replaced. If cracks are evident in rotor, replace rotor.
- Mount Dial Indicator (Special Tool C-3339) on caliper adapter. Dial indicator plunger should contact braking surface of rotor approximately 10 mm (.393") from outer edge of rotor. See Figure . Check lateral runout on both sides of rotor. Lateral runout of rotor should not exceed .13 mm (.005").
- If lateral runout of rotor is in excess of specification, check lateral runout of hub face with rotor removed. Before removing rotor from hub, make a chalk mark across both rotor and one wheel stud on high side of runout. See Figure . This will ensure that original location of rotor in relation to hub can be retained .
- Remove brake rotor from hub. Thoroughly clean front surface of flange on hub/bearing. Install Dial Indicator, (Special Tool C-3339) on caliper adapter.NOTE: The front face of hub flange must be thoroughly cleaned before checking hub for runout.
- Position stem on dial indicator so it contacts hub face near outer diameter. See Figure . Care must be taken to position stem outside stud circle but inside chamfer on hub face. Lateral runout should not exceed .08 mm (.003"). If runout exceeds this specification, hub MARK must be replaced. If lateral runout of hub does not exceed this specification, install rotor on hub with chalk marks two wheel studs apart. See Figure . Tighten nuts in proper sequence to required torque specification. Finally, check lateral runout of rotor to see if lateral runout is now within specification. If lateral runout is not within specification on a front brake rotor, install a new brake rotor, or reface it. If refacing a front brake rotor, be careful to remove as little rotor material as possible from each side of rotor. Remove equal amounts from each side of rotor. DO NOT reduce thickness below minimum thickness marking cast into un-machined surface of rotor. See Figure . If lateral runout is not within specification on a rear brake rotor, install a new brake rotor only. Although minimum thickness marking is cast into un-machined surface of rear rotor. See Figure . Rear rotors must only be replaced.
- Install disc brake caliper on caliper adapter. Install wheel/tire on hub. Tighten wheel mounting nuts in proper sequence until all nuts are torqued to half required torque specification. Then repeat tightening sequence to full specified torque of 135 N.m (100 ft. lbs.)