Express 1/2 Ton Van V8-305 5.0L VIN M SFI (1998)
Brake Rotor/Disc: Service and Repair
Refinishing Brake Rotors
DESCRIPTION
You do not need to refinish the brake rotors when doing a routine brake maintenance such as replacing worn brake shoe and lining assemblies.
Refinish the rotors only in the cases of brake pulsation, hot spots, or excessive scoring.
The brake rotors have a minimum thickness dimension cast into them. This dimension is the minimum wear dimension, it is not a refinish dimension.
Do not use a brake rotor that will not meet the dimensions shown in the specifications chart after refinishing. Refer to Component Specifications in
Disc Brakes. Replace any rotors which are too thin as they will not have the proper heat transfer capabilities. Refinishing the composite rotors requires
the use of J 39144.
An accurate control of the rotor tolerances is necessary for the proper performance of the disc brakes. Use precision equipment for all of the
machining. Service the machining equipment on a regular basis following the manufacturer's recommended maintenance procedures.
When refinishing the rotors, make sure the attaching adapters, tool holders, vibration dampeners, and tool bits are in good condition. Make sure that
all cutting tools or bits are sharp and use only the replacement cutting bits recommended by the equipment manufacturer. Any dull or worn tools will
leave a poor surface finish that will affect the initial brake performance. Always use vibration dampening attachments when refinishing the braking
surfaces. The vibration dampening attachments will eliminate tool chatter in order to allow for a better surface finish. Keep the vibration dampening
attachments clean and free of nicks.
The following are the recommended procedures that achieve adequate results using two different off-vehicle drum/disc brake lathes, the Ammco
Brake Lathe and the Accu Turn Lathe (GM dealer equipment) off-vehicle brake drum and brake rotor lathes. Follow the manufacturer's instructions
and recommendations when using any other brake lathe. Refer to Brake Lathe Specifications in Disc Brakes.
REFINISHING PROCEDURE
1. Make the brake rotor surface non-directional.
2. 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 Accu Turn 433179 Non-Directional Swirl Finisher. As an alternate method, use a sanding block with
150 grit aluminum oxide sandpaper.
3. Sand each brake rotor surface using moderate pressure for at least 60 seconds.
4. With the brake rotor turning at about 150 RPM, sand each brake rotor surface using moderate pressure for at least 60 seconds.
5. Clean each brake rotor surface with denatured alcohol or a substitute cleaner after sanding.
6. 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.
7. Zero the scale and back out the tool bits.
8. Advance the cutter hand-wheel until the bits have cleared the inner edge of the brake rotor face.
9. 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.
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.
