SERVICE PROCEDURES
CHECKING BRAKING DISC FOR RUNOUT AND
THICKNESS
On vehicle, braking disc (rotor) runout is the combi-
nation of the individual runout of the hub face and the
runout of the disc. (The hub and disc are separable). To
measure runout on the vehicle, remove the wheel and
reinstall the lug nuts tightening the disc to the hub.
Mount Dial Indicator, Special Tool C-3339 with Mount-
ing Adaptor, Special Tool SP-1910 on steering arm.
Dial indicator plunger should contact disc (braking
surface) approximately one inch from edge of disc (See
Fig. 1). Check lateral runout (both sides of disc) runout
should not exceed 0.13 mm (0.005 inch).
If runout is in excess of the specification, check the
lateral runout of the hub face. Before removing disc
from hub, make a chalk mark across both the disc and
one wheel stud on the high side of runout. So you’ll
know exactly how the disc and hub was originally
mounted (Fig. 2). Remove disc from hub.
Install Dial Indicator, Special Tool C-3339 and
Mounting Adaptor, Special Tool SP-1910 on steering
knuckle. Position stem so it contacts hub face near
outer diameter. Care must be taken to position stem
outside the stud circle but inside the chamfer on the
hub rim. Clean hub surface before checking. (See
Fig. 3)
Runout should not exceed 0.08 mm (0.003 inch). If
runout exceeds this specification, hub must be re-
placed. See Suspension Group 2. If hub runout does not
exceed this specification, install disc on hub with chalk
marks two wheel studs apart (Fig. 4). Tighten nuts in
the proper sequence and torque to specifications. Fi-
nally, check runout of disc to see if runout is now within
specifications.
If runout is not within specifications. Install a new
braking disc or reface disc, being careful to remove as
little as possible from each side of disc. Remove equal
amounts from each side of disc. Do not reduce thick-
ness below minimum thickness cast into the un-
machined surface of the rotor.
Thickness variation measurements of disc should be
made in conjunction with runout. Measure thickness of
disc at 12 equal points with a micrometer at a radius
approximately
25.4
mm
(1
inch)
from
edge
Fig. 1 Checking Braking Disc for Runout
Fig. 2 Marking Braking Disc and Wheel Stud
Fig. 3 Checking Hub for Runout
.
BRAKES
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