Rotor Refinishing

Do not refinish rotors when performing routine brake maintenance such as replacing worn rear disc brake inner and outer pads. Refinish a rotor only under the following circumstances:
1. There is a complaint of brake pulsation.
2. There is scoring greater than 1.5 mm (0.060 inch).

All rotors have a minimum thickness dimension cast into them. This dimension is the minimum wear dimension and not a refinish dimension. The minimum refinish dimension is greater than the discard dimension, Do not use a rotor that will not meet specifications. A rotor that is too thin will not have the proper heat transfer capabilities. Replace it with a new rotor.

Since accurate control of rotor tolerances is necessary for the proper performance of the rear disc brakes, the rotor should be machined only with precision equipment. Equipment should be serviced on a regular basis following the manufacturer's recommended maintenance procedure. When refinishing rotors, the attaching adapters, tool holders, vibration dampeners, and tool bits must be in good condition. Always use sharp cutting tools or bits and use only replacement cutting bits recommended by the equipment manufacturer. Dull or worn tools leave a poor surface finish which will affect brake performance and possibly cause brake chatter while machining. Vibration dampening attachments should always be used when refinishing braking surfaces. These attachments help eliminate tool chatter and will result in better surface finish. Make sure these adapters are clean and free of nicks.

On-Vehicle
Tools Required:
J 39144 On-Vehicle brake lathe or equivalent
In the cases where rotors are being refinished to correct a problem with brake pulsation, it is recommended that an on-vehicle brake lathe be used to achieve best results. Follow the equipment manufacturer's recommended specifications and procedure.

Off-Vehicle
Accuturn Brake Lathe, GM Dealer Equipment
(One-cut refinishing procedure)
Locate the deepest score and turn the tool bit micrometer knob until the tool bit bottoms out at the deepest point of the score. Zero the scale and back out the tool bit (repeat for opposite side of rotor). Advance the cutter handwheel until the bits have cleared the inner edges of the rotor face. Adjust the micrometer knobs for approximately 0.13 mm (0.005 inch) more than the first reading. This will ensure resurfacing the rotor in one cut.
Spindle Speed 105 rpm
Depth of Cut As Necessary
Tool Cross Feed 0.08 mm (0.003 inch) per rev.
Tool Bit Nose Radius 1/64
Vibration Dampener Yes
Non-Directional Finishing Yes


AMMCO BRAKE LATHE
(Two-cut refinishing procedure)
Rough Cut
Spindle Speed 150 rpm
Depth of Cut (per side) 0.15 - 0.64 mm (0.006 - 0.025 inch)
Total Cross Feed (per revolution) 0.25 mm (0.010 inch)
Vibration Damper Yes
Sand Rear Brake Rotor (Swirl Pattern) No

Finish Cut
Spindle Speed 150 rpm
Depth of Cut (per side) 0.010 - 0.015 mm (0.004 - 0.006 inch)
Total Cross Feed (per rev.) 0.05 mm max (0.02 inch)
Swirl Pattern YES

Non-Directional Finishing
It is very important that the rotor surface be made non-directional by dressing the rotor surfaces with a sanding disc tool such as Accuturn 433179 Non-Directional Swirl Finisher, Ammco 8750 Safe Swirl Disc Rotor Grinder, or equivalent, using 120 frit aluminum oxide sandpaper. Sand each rotor surface with moderate pressure for a minimum of 60 seconds. If the brake lathe is not equipped with an adequate non-directional finishing tool, an alternate method is to use a sanding block with 150 grit aluminum oxide sandpaper. With the rotor turning at the equipment manufacturer's highest recommended cutting speed, sand each rotor surface for a minimum of 60 seconds using moderate pressure. After the rotor has been sanded, clean each surface with denatured alcohol or a suitable brake cleaner. The finished rotor surface should be as close to that of a new rear brake rotor as passible. Failure to obtain the best possible finish may affect braking performance.

NOTE: Rear brake rotors should always be replaced if turning will result in a rear brake rotor that does not meet manufacturer specifications for minimum thickness. When installing new brake rotors, do not refinish the surfaces of these parts. New brake rotors have the correct level of surface finish.

Refinishing Rear Brake Rotor Parking Brake Surface
The rear brake rotor parking brake contact surface should not be refinished. If the parking brake system cannot effectively hold the vehicle and all other parking brake components are functioning properly, replace the rotor.