Turning Rotors off the Vehicle
After the rotor is removed from the vehicle, bring it to
the brake lathe. If the rotor is an integral type, remove the
grease seal and inner bearing and clean all grease from the
interior of the hub. Check the brake lathe arbor and rotor
adapters for dirt and metal, and clean as needed. Make
sure the cutters are sharp and tightly attached. Inspect the
lathe and be certain that all other parts, including shields,
are solidly attached and in good working condition.
Install the rotor on the brake lathe using the proper
adapters, Figure 13-29A. Consult the lathe makers manual
if you have any doubts as to how this should be done. If
you have not checked the rotor’s thickness or have any
questions as to the thickness, check the rotor with a
micrometer, Figure 13-29B. Then install the silencer band,
Figure 13-29C, on the outer edge of the rotor.
The silencer band reduces noise, but more impor-
tantly, eliminates vibration in the rotor as it is being cut.
Vibration will cause tool chatter (a rapid bouncing of the
tool against the rotor surface) as the bit cuts. This will pro-
duce a rough “wood grain” surface on the rotor. The rotor
will need to be recut, unnecessarily removing metal. If you
forget to install the band, the rotor will chatter as soon as
the bits start cutting. Turn the lathe off immediately and
install the silencer band. Then begin the cut again.
Start the brake lathe and check that the rotor is turn-
ing smoothly. Then turn the feed dials of each cutter until
they are near the rotor surface. Be sure the cutters are
directly across from each other. Slowly turn the cutter
assembly until the cutters are in approximately the center
of the rotor braking surface. Then slowly turn one cutter
feed dial until the cutter tip just touches the rotor surface.
Hold the feed dial and turn the numbered collar to zero,
Figure 13-30. Repeat this operation for the other cutter.
Move the cutters to the innermost part of the rotor; do
not ground the tip in the corner between the rotor hub and
braking surface. Then adjust the cut and feed speed. A cut
made to remove a great deal of metal, with the speed set
relatively high is a rough cut. A cut made to remove a
small amount of metal at slow feed speeds is a finish cut.
The amount and speed of cutting will be governed by
the total amount to be removed and the finish desired,
Figure 13-30. If the rotor is deeply grooved, a great deal of
metal must be removed to obtain a smooth finish on the
rotor. In this case, it will be necessary to make several
rough cuts before making the finish cut. If the rotor is only
lightly damaged, or just requires that a shiny surface be
removed, it may be refinished by a single finish cut.
To make a rough cut, set the cutters to the maximum
cutting depth and set the speed to a relatively fast setting.
As a general rule, take no more than .006” (.152 mm) from
each side on any single cut. Check the collars on the lathe
cutters to determine whether they are scribed in thou-
sandths of an inch or in millimeters.
After cutting depth and feed speed are established,
engage the feed lever and watch the rotor as it cuts. Allow
the cutting blades to cut the entire braking surface and exit
the outer edge of the rotor. Then disengage the feed lever
and inspect both rotor surfaces. If the first cut left grooves
or shiny spots, repeat the rough cut as needed. After all
damaged areas are removed, make a finish cut.
222 Auto Brakes
Figure 13-28. Rotor removal. A—Some rotors are attached to
the hub with screw fasteners. B—Integral rotors house the
Note: Some front-wheel drive rotors
require the use of a special hub adapter,
which has lugs, much like the vehicle’s
wheel hub. Check the service manual.
Caution: Remove only enough metal to clean
up imperfections. Careless cutting may
make an otherwise machinable rotor too thin
and it will require replacement. If the imperfections
are too deep, replace the rotor. Cutting too much at
once can also cause the tips to wear prematurely or