Brake Rotor
OVERVIEWCAUTION: The rear brake rotor used on this vehicle cannot be machined. If when diagnosing the rear rotor for thickness variation and runout it is found not to meet the required specifications, the rotor must be replaced. No attempt should ever be made to machine the rear brake rotor.
Any servicing of the rotor requires extreme care to maintain the rotor to within service tolerances to ensure proper brake action.
The rear brake rotor is made of aluminum silica carbide alloy and must not be machined. The rear brake rotor has two slits cut into the braking surface. They are there to isolate rear brake noise. These should be inspected to make sure they are clear of debris.
Before refinishing or refacing a front brake rotor, the rotor should be checked and inspected for the following conditions:
Braking surface scoring, rust, impregnation of lining material and worn ridges.
Excessive rotor lateral runout or wobble.
Thickness variation in braking surface of the rotor (Parallelism).
Dishing or distortion in braking surface of the rotor (Flatness).
If a vehicle has not been driven for a period of time, the rotors will rust in the area not covered by the brake lining and cause noise and chatter when the brakes are applied.
Excessive wear and scoring of the rotor can cause temporary improper lining contact if ridges are not removed from braking surface of rotor before installation of new brake shoes.
Some discoloration and/or wear of the rotor surface is normal and does not require resurfacing when linings are replaced.
Excessive runout or wobble in a rotor can increase pedal travel due to piston knock-back. This will also increase guide pin bushing wear due to the tendency of the caliper to follow rotor wobble.
Thickness variation in a rotor can also result in pedal pulsation, chatter and surge due to variation in brake output. This can also be caused by excessive runout in the rotor and/or the hub.
Dishing or distortion can be caused by extreme heat and abuse of the brakes.
CHECKING ROTOR FOR THICKNESS AND RUNOUT
NOTE: The procedure for checking rotor runout and thickness is the same for the front and rear rotor. If there is a specification difference between the front and rear rotor it will be designated as such in the specifications of the following procedure.
On-vehicle rotor runout is the combination of the individual runout of the hub face and the runout of the rotor. (The hub and rotor runout readings are separable). To measure runout on the vehicle use the following procedure.
1. Remove the tire and wheel from the hub.
2. Reinstall the wheel mounting nuts. Tightening the rotor to the hub using the wheel mounting nuts. Tighten the wheel mounting nuts to the specified torque of 135 Nm (100 ft. lbs.)
3. Remove the disc brake caliper from the caliper adapter. Refer to Disc Brake System, Brake Caliper, Service and Repair, (Front) Removal And Installation for the procedure if required.
Thickness variation measurements of the rotor should be made in conjunction with the lateral runout measurements. Measure the thickness of the rotor at 12 circumferentially equal points with a micrometer at a radius approximately 25.4 mm (1 inch) from outer edge of rotor. If thickness measurements vary by more than 0.013 mm (0.0005 inch), 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, the rotor must be refinished or replaced (See Refinishing/Refacing Rotor). If cracks are evident in the rotor, replace the rotor.
4. Mount Dial Indicator, Special Tool C-3339 on the caliper adapter.
5. Dial indicator plunger should contact braking surface of rotor approximately 10 mm (0.393 inch) from outer edge of rotor.
6. Check lateral runout on both sides of the rotor. Lateral runout of the rotor should not exceed 0.13 mm (0.005 inch).
7. If lateral runout of the rotor is in excess of the specification, check the lateral runout of the hub face with the rotor removed. Before removing rotor from hub, make a chalk mark across both the rotor and one wheel stud on the high side of the runout. This will ensure that the original location of the rotor in relation to the hub can be retained.
8. Remove the brake rotor from the hub.
9. Thoroughly clean the front surface of the flange on the hub/bearing.
10. Install Dial Indicator, Special Tool C-3339 on the caliper adapter.
NOTE: The front face of the hub flange must be thoroughly cleaned before checking hub for runout.
11. Position stem on dial indicator so it contacts hub face near outer diameter. Care must be taken to position stem outside the stud circle but inside the chamfer on the hub face.
Lateral runout should not exceed 0.08 mm (0.003 inch). If runout exceeds this specification, the hub must be replaced. See Steering and Suspension, Suspension, Wheel Hub, Service and Repair. If lateral runout of the hub does not exceed this specification, install rotor on hub with chalk marks two wheel studs apart. Tighten nuts in the proper sequence to the 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 the 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 the un-machined surface of the rotor.
If lateral runout is not within specification on a rear brake rotor, install a new brake rotor only. Although the minimum thickness marking is cast into the un-machined surface of the rear rotor, rear rotors must only be replaced.
12. Install disc brake caliper on caliper adapter.
13. Install the wheel/tire on the hub.
14. Tighten the wheel mounting nuts in the proper sequence until all nuts are torqued to half the required torque specification. Then repeat the tightening sequence to the full specified torque of 135 Nm (100 ft. lbs.)