Brake Rotor Inspecting and Machining
INSPECTING AND REFINISHING BRAKE ROTORSIn manufacturing the brake rotor, tolerances of the braking surfaces for flatness, parallelism, and lateral runout are held very close. The maintenance of close tolerances on the shape of the braking surfaces is necessary to prevent brake roughness and brake noise.
In addition to these tolerances, the surface finish must be held to a specified range. The control of the braking surface finish is necessary to avoid pulls and erratic performance and to extend lining life.
When performing routine brake maintenance, rotors should not be refinished, unless there is a brake pulsation caused by the rotors or the rotors are excessively scored.
Scoring of the rotor surfaces not exceeding 1.5 mm (0.060 inch) in depth, which may result from normal use, is not detrimental to brake operation.
THICKNESS VARIATION CHECK
Thickness variation can be checked by measuring the thickness of the rotor at four or more points around the circumference of the rotor. All measurements Must be made at the same distance in from the edge of the rotor. Use a micrometer graduated in 0.002 mm (0.002 mm).
A rotor that varies in thickness by more than 0.0 13 mm (0.0005 inch) can cause pedal pulsation and/or front end vibration during brake applications. A rotor that does not meet these specifications should be refinished to specifications or replaced.
LATERAL RUNOUT CHECK
1. Remove road wheel and install two wheel nuts on opposite studs.
2. Fasten a dial indicator graduated in ten-thousandths of an inch (0.0025 mm 10.0001 inch) to steering knuckle so the indictor stylus contacts the rotor about 10 mm (0.40 inch) from rotor edge.
3. Zero the dial indicator.
4. Move rotor one complete revolution and observe Total Indicated Runout (TIR).
Maximum Combined Hub, Bearing and Rotor Lateral Runout: 0.035 mm (0.0013 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 boll 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 0.013 mm (0.0005 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 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 the rotor tolerances 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 refinish dimension cast into them. Their dimension is the minimum refinished dimension and allows for additional wear. Do not use a brake rotor that does not meet the specifications as shown in the specifications.
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 (tips, bits). Dull or worn inserts leave it Pool-surface finish which will affect initial braking performance.
Make sure brake lathe is clean and free of debris before turning rotors. Remove metal filings from the mating surface between lathe and cutting assembly. Remove filings from behind tool bit holders.
Some brake lathes (Accu-Turn or equivalent) can refinish a rotor's surface with one cut, regardless of the depth. HOWEVER, ROTOR MUST NOT VIBRATE DURING REFINISHING OPERATION. Use the vibration dampening devices provided with the lathe.
Manufacturers of brake lathes that cannot control rotor vibration during deep cuts recommend several cuts to achieve desired finish. Following the instructions provided with the lathe will help ensure high-quality machining. Again, always use the vibration dampening devices provided of lathe.
Regardless of brake lathe used, a shallow finish Cut Will not yield 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.
IMPORTANT: 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 on brake lathe, sand each side of rotor for a minimum of 90 seconds with 150 grit sandpaper Mounted on a sanding block. Use moderate pressure. After sanding, clean 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.
CAUTION: 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.