Refinishing Rotors
Do not refinish brake rotors when doing routine maintenance, such as
replacing worn disc brake pads. Refinish a rotor only under the following
circumstances:
- There is a complaint of brake pulsation.
- There is scoring greater than 1.5 mm (0.060 in)
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, after refinishing, will not meet the specifications
shown on the rotor. Always replace it with a new rotor.
Accurate control of rotor tolerance is necessary for proper performance
of the disc brakes. Machining of the rotor should be done only with precision
equipment. Machining equipment should be serviced on a regular basis following
the manufacturer's recommended maintenance procedures.
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
braking performance.
Vibration dampening attachments should always be used when refinishing
braking surfaces. These attachments eliminate tool chatter and will result
in better surface finish. Make sure these adapters are clean and free of
nicks.
Brake Lathe
It is recommended that an on-vehicle brake lathe be used in cases where
rotors are being refinished to correct a problem with brake pulsation. Follow
the equipment manufacturer's recommended specifications and procedures.
The following are two recommended procedures for using two different
off-vehicle drum/disc brake lathes (if any other lathe is used, follow that
lathe's instructions and recommendations.)
When using the AMMCO Brake Lathe:
| • | Depth of Cut (per side): |
| - | Rough cut, 0.1524--0.6350 mm (0.006--0.025 in). |
| - | Finish cut, 0.1016--0.1524 mm (0.004--0.006 in). |
| - | Rough cut, 0.254 mm (0.010 in). |
| - | Finish cut, 0.0508 mm (0.002 in). |
When using the ACCU*TURN® Brake Lathe, GM Dealer Equipment (one-cut
refinishing procedure), locate the deepest score and turn the rotor 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 the opposite side of the
rotor). Advance the cutter handwheel until the bits have cleared the inner
edge of the rotor face. Adjust the micrometer knobs for about 0.127 mm
(0.005 inch) more than the first reading. This will ensure resurfacing
of the rotor in one cut.
| • | Spindle Speed: 105 rpm. |
| • | Depth of Cut: As necessary. |
| • | Cross Feed (per rev): 0.0762 mm (0.003 in). |
| • | Tool Bit Nose Radius: 1/64. |
It is very important that the rotor surface be made non-directional
by dressing the rotor surfaces with a sanding disc tool, such as an AMMCO
Model 8750 Safe Swirl Disc Rotor Grinder, Accuturn 433179 Non-directional
Swirl Finisher, or equivalent, using a 120 grit 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 as possible to that of
a new rotor. Failure to obtain the best possible rotor finish may affect braking
performance.
After replacing pads and/or refinishing rotors, break in or burnish
the new braking surfaces. This can be done by making 20 stops from 48 km/h
(30 mph), using medium to firm pedal pressure. Take care to not overheat
the brakes.
