Chevrolet Light Duty Truck 1973, Service Manual

Page: 301 / 979

BRAKES 5 -3 5
M U ST NOT BE C IR C U M F E R E N T IA L
(D IR EC TIO N A L)
The disc in Figure 65 has a preferred non-
directional finish that is achieved with a flat
sanding disc.
3.
BOTH SU RFA CES M UST BE FLA T W ITHIN .002
T.I.R.
This specification must be met to prevent surface
taper that could wear shoes on an angle (fig.
66
).
4.
M UST BE P A R A LLEL W ITH EACH O THER W ITHIN
.003 T.I.R. WHEN C H E C K E D RADIALLY.
Disc surfaces, which are not parallel, can cause
shoes to wear on an angle (fig. 67).
5.
WHEN MOUNTED ON BEA RIN G C U PS, LA TER A L
RUN-OUT M UST NOT E X C E ED .005 T.I.R. AND
M AXIM UM RATE OF C H A N G E M U ST NOT
EX C EED .001 IN 30 4
Proper lateral runout will prevent disc "wobble"
that could knock the piston back into the caliper
bore causing increased pedal travel.
To check lateral runout, tighten the wheel
Fig. 65 -Disc Non-Directional Finish
bearing adjusting nut until all of the play is out
of the bearing. It should be just loose enough to
allow the wheel to turn. Mark the disc with chalk
every 30° (fig.
68
). Fasten a dial indicator to
some portion of the suspension so that the point
of the stylus contacts the rotor face approx­
imately one inch from the rotor edge. Set the
dial at zero and move the rotor one complete
rotation, checking the indicator as the rotor
moves. After checking the runout, readjust the
wheel bearing (See Section 3).
6
.
TO TA L C IR C U M FE R E N T IA L T H IC K N E S S VARIA­
TION AT ANY RAD IUS M UST NOT E X C E ED .0005
IN 360,
Excessive disc thickness variation will cause
brake pedal pulsation.
To check for parallelism, measure the thickness
of the rotor at four or more points around the
circumference of the rotor. All measurements
must be made at the same distance in from the
edge of the rotor.
Place indicators opposite each other and set to
Fig. 6 8 -Checking Lateral Run-Out
MARK DISC
WITH CHALK
EVERY 30°
MAXIMUM
RUN OUT .005
WITH MAXIMUM
OF .001 IN 30°
LIGHT DUTY TRUCK SERVICE MANUAL