GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Astro - 4WD 🢒 Brakes 🢒 Hydraulic Brakes 🢒 Brake Rotor Refinishing

Tools Required

J 37704 Disc Brake Lathe

       Important: It is not necessary to refinish the brake rotors when replacing the brake shoe and the lining pads assemblies.

    • Refinish the brake rotors only under the following conditions:
       - The brakes are pulsating.
       - The brake rotor has hot spots.
       - The brake rotor is scored greater than 1.5 mm (0.060 in).
       - The brake rotor is beyond specifications.
    • The brake rotors have a minimum thickness cast into them. This is the minimum wear dimension and not a refinish dimension. Replace a brake rotor that will not meet the specified dimensions after refinishing. Refer to Component Specifications . A rotor that is too thin will not have the proper heat transfer capabilities.
    • The proper performance of disc brakes requires accurate control of rotor tolerances.
    • Use only precision equipment in machining.
    • Regularly service the machine equipment, using the manufacturer's recommended procedures for maintenance.
    • When refinishing rotors, do the following:
       - Make sure that all tools, adapters, holders, vibration dampeners, and tool bits are in good condition.
       - Use sharp cutting tools and tool bits. Dull or worn tools leave a poor surface finish that affects initial brake performance.
       - Use replacement cutting tool bits the equipment manufacturer recommends.
       - Use only vibration-dampening attachments while refinishing brake surfaces. These eliminate tool chatter, thereby promoting a better finish.
       - Make sure the adapters are clean and free of nicks.
    • The Ammco Brake Lathe and the Accuturn Brake Lathe (GM dealer equipment) are recommended off-vehicle brake rotor and drum lathes that achieve good results. Follow the manufacturer's recommendations and instructions for initial setup and cutting procedures when using any brake lathe.
    • Make the brake rotor surface non-directional.
       - Dress the brake rotor surfaces with a sanding disc power tool using 120 grit aluminum oxide sandpaper. Use a tool such as the Ammco 8350 or 8750 Safe Swirl Brake Rotor Grinder, or the Accuturn 433179 Non-Directional Swirl Finisher.
       - As an alternate method, use a sanding block with 150 grit aluminum oxide sandpaper.
       - Sand each brake rotor surface using moderate pressure for at least 60 seconds.
       - With the brake rotor turning at about 150 RPM, sand each brake rotor surface using moderate pressure for at least 60 seconds.
       - Clean each brake rotor surface with denatured alcohol or a substitute cleaner after sanding.

Refinishing Procedure
  1. Locate the deepest score in the brake rotor. Turn the rotor micrometer knobs until the tool bit bottoms out at the deepest point of the score.
  2. Zero the scale and back out the tool bits.
  3. Advance the cutter hand-wheel until the bits have cleared the inner edge of the brake rotor face.
  4. Adjust the micrometer knobs about 0.0127 mm (0.005 in) more than the first reading. This will ensure clearing the brake rotor in one cut.
  5. The finished brake rotor surface should be as close to that of a new brake rotor as possible. Failure to obtain the best possible brake rotor finish can affect initial braking performance.