Brake Rotor Assembled Lateral Runout (LRO) Measurement
LATERAL RUNOUT CHECK1. Remove road wheel and install two wheel nuts 180 degrees apart to retain rotor.
2. Fasten a dial indicator graduated in ten-thousandths of an inch (0.0001 inch [0.002 mm]) to the steering knuckle so that the indictor stylus contacts the rotor about 10 mm (0.40 inch) from the rotor edge.
3. Zero the dial indicator.
4. Move the rotor one complete revolution and observe Total Indicated Runout (TIR).
Maximum Combined Hub, Bearing, and Rotor Lateral Runout: 0.060 mm (0.0024 inch)
Lateral runout of the rotor, if excessive, can often be improved by cleaning dirt and rust from hub and rotor mating surfaces, and/or indexing the rotor on the hub one or two bolt positions from the original position. If the lateral runout cannot be corrected by indexing the rotor, check the hub and bearing assembly for excessive lateral runout. If the hub and bearing assembly lateral runout exceeds 0.040 mm (0.0016 inch), replace the hub and bearing assembly. If lateral hub and bearing runout is within specifications, refinish or replace the rotor as necessary. If installing a new rotor, inspect the inside hub mating surface. Runs in the paint should be sanded off prior to installing a new rotor.
REPLACING BRAKE ROTORS
When installing new brake rotors, do not refinish the surfaces as these parts are at the correct level of surface finish.
REFINISHING BRAKE ROTORS
Accurate control of rotor tolerance is necessary for proper performance of the disc brakes. Machining of rotors should be done only with precision equipment.
All brake rotors have a minimum thickness dimension cast into them. This dimension is the minimum wear dimension and not a refinish dimension. Do not use a brake rotor that does not meet the specifications as shown in the specifications at the beginning of this section.
If rotors are removed, remove rust and scale from the rotor/hub and rotor/wheel mating surfaces. Failure to do so can cause excessive lateral runout when the rotor is mounted on the brake lathe or when the rotor is installed to the hub.
When refinishing rotors, always use sharp cutting inserts (bits, tips). Dull or worn inserts leave a poor surface finish, which will affect braking performance. Make sure the brake lathe is clean and free of debris before turning rotors. Remove metal filings from the mating surface between the lathe and the cutting assembly. Remove filings from behind the tool bit holders.
Some brake lathes (Accu-turn or equivalent) can refinish a rotor's surface with one cut, regardless of the depth. However, the rotor must not vibrate during the refinishing operation. Use the vibration damping devices provided with the lathe.
Manufacturers of brake lathes that cannot control rotor vibration during deep cuts recommend several cuts to achieve the desired finish. Following the instructions provided with the lathe will help ensure high-quality machining. Again, always use the vibration dampening devices provided with the lathe.
Regardless of the brake lathe used, a shallow finish cut will not yield the best surface finish. A shallow cut of 0.051 mm (0.002 inch) "smears" the rotor's surface, creating a rougher-than-desired finish. Cutting at least 0.127 mm (0.005 inch) (per side) will leave a smoother surface, resulting in better brake performance.
Make sure to use the proper cutting inserts. Use the cutting inserts recommended by the brake lathe's manufacturer. Check the cutting inserts' condition regularly. Replace them at the first sign of inferior refinishing. Following all the lathe's machining instructions will facilitate acquiring the desired surface finish.
All brake lathes use a single-point cutting tool. This tool will not yield the necessary surface finish. A secondary finishing operation must be performed. To obtain the necessary finish, follow this procedure: With the rotor turning in the brake lathe, sand each side of the rotor for a minimum of 90 seconds with 150 grit sand paper mounted on a sanding block. Use moderate pressure. After sanding, clean the rotor thoroughly. Use Saturn Brake Cleaner P/N 21007432 (or equivalent).
CAUTION:THE SURFACE FINISH QUALITY OF A MACHINED ROTOR SHOULD BE AS HIGH AS A NEW ROTOR. FAILURE TO OBTAIN THIS BEST POSSIBLE ROTOR SURFACE FINISH WILL NEGATIVELY AFFECT BRAKING PERFORMANCE. ROTORS OR DRUMS SHOULD ALWAYS BE REPLACED IF MACHINING RESULTS IN A ROTOR OR DRUM THAT DOES NOT MEET THE MANUFACTURER'S SPECIFICATIONS FOR MINIMUM ROTOR THICKNESS OR MAXIMUM DRUM DIAMETER.