Surface Tolerance And Finish; Rotor Service; Lateral Runout Check; Parallelism Check - Pontiac Grand Prix Service Manual

DISC BRAKES 5E-7
REPLACE
1. Install new bearings or seal as necessary.
2. Install hub and rotor assembly on spindle. See
Section 3 for proper Wheel Bearing Adjustment
Procedure.
3. Install caliper assembly and torque mounting bolts
to 35 Ib. ft. (See Caliper
-
Install).
4. Install wheel and tire assemblies, and torque lug
nuts to 75 lb. .ft. (Pontiac), and 70 Ib. ft. (Tempest,
Grand Prix, and Firebird).
5. Depress brake pedal several times to seat linings on
rotor.
CA UTZOPI: Do not move car until a firm brake pedal
is
obtained.
ROTOR SERVICE
LATERAL RUNOUT CHECK
(CHECK ROTORS ONLY WHEN A SPECIFIC
COMPLAINT POINTS TOWARD A PROBLEM IN
THIS AREA.)
Lateral runout is the movement of the rotor from side
to side as it rotates. This could be described as "rotor
wobble".
The movement of .the rotor from side to side in the
lateral plane causes the brake shoe and lining and
pistons to be knocked back into their bores. This
results in additional pedal travel required and a
vibratiorl during the braking action.
To check lateral runout (Fig. 5E-15) first adjust the
wheel bearings until all of the end play is eliminated.
Fasten a dial indicator to some portion of the
suspension so the stylus contacts the rotor face
approximately one inch from the rotor edge. Set the
dial at zero. Move. the rotor one complete rotation,
checking the indicator as the rotor moves.
For lateral runout specifications see
-
SPECIFICA-
TIONS.
PARALLELISM CHECK
rotor. Measurements must be made at the same
distance from the edge of the rotor and an indicator
which reads .0001" must be used.
A rotor that varies beyond the recommended specifica-
tions (see
-
SPECIFICATIONS) causes pedal vibra-
tion, as well as front end vibration during brake
applications. A rotor that does not meet the specifica-
tions must be discarded and replaced with a new rotor.
Field equipment cannot machine the rotor to specifica-
tion.
SURFACE TOLERANCE AND FINISH
In manufacturing the brake rotor, tolerances of the
rubbing surfaces for flatness, for parallelism and for
lateral runout are held very close. The maintenance of
these close controls on the shape of the rubbing
surfaces is necessary to prevent brake roughness.
In addition to these tolerances the surface finish &st
be held to a specified range. The control of the
rubbing surface finish is necessary
to
avoid pulls and
erratic performance and to extend lining life.
The rotor tolerances are.listed in the Specification
Section.
Parallelism is the measurement of the thickness of the
rotor at any point around the circumference of the
I
J
Fig. 5E-14 Seating Boot