Chevrolet LIGHT DUTY TRUCK (SERIES 10-35) Service Manual page 428

indicator as the rotor moves.
4. Lateral runout should not be over .004" total
indicator reading.
Parallelism Check
1 . Parallelism is the measurement of 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.
2. A rotor that varies over .0005" causes pedal
vibration, as well as front end vibration during brake
applications. A rotor that does not meet these specifications
may be refinished to specifications if precision equipment
is available.
Rotor Tolerance and Surface Finish
In manufacturing the brake rotor, tolerances of the
rubbing surfaces for flatness, for parallelism and for lateral
runout are held very closely. The maintenance of these close
controls on the shape of the rubbing surfaces is necessary
to prevent brake roughness.
In addition to these tolerences, the surface finish must
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.
Light scoring of the rotor surfaces not exceeding .015"
in depth, which may result from normal use, is not
detrimental to brake operation.
Machining
Since accurate control of the rotor tolerances is
necessary for proper performance of the disc brakes,
machining of the rotor should be done only with precision
equipment.
CAUTION: All brake
minimum thickness dimension cast into
them. This dimension is the minimum
wear dimension
dimension. Do not use a brake rotor that
will not meet the specifications, as shown
below, after refinishing. Replace with
new brake rotor.
ROTOR THICKNESS
MINIMUM
AFTER REFINISHING
1.480
1.230
.980
Wheel Bolt Replacement (Disc Brakes)
1 . Remove hub and rotor assembly from vehicle.
2. Mark rotor to hub location and remove bolts
attaching hub to rotor.
3. The wheel bolts on disc brakes can be pressed out
from the outside of the hub and installed from inside the
rotor by pressing into place. No drilling or cutting is
required.
rotors have a
and not a refinish
REPLACEMENT
(DISCARD)
1.465
1.215
.965
4. Reinstall assembly and adjust wheel bearings.
DRUM BRAKE SHOE AND LINING
Service Brake
Adjustment
1 . Using a punch, knock out lanced area in brake drum.
If this is done with the drum installed on the vehicle, the
drum must be removed and all metal cleaned out of the
brake compartment. Be sure to procure a new
cover and install it in the drum after adjustment to prevent
dirt and water from getting into the brakes. Use J-6166 to
turn brake adjusting screw; expand brake shoes at each
wheel until the wheel can just be turned by hand. The drag
should be equal at all wheels.
2. Back off brake adjusting screw at each wheel 30
notches. If shoes still drag lightly on drum, back off
adjusting screw one or two additional notches. Brakes
should be free of drag when screw has been backed off
approximately 12 notches. Heavy drag at this point
indicates tight parking brake cables.
3. Install metal adjusting hole cover in brake drum.
4. Check parking brake adjustment.
Removal and Inspecting
CAUTION: See "Caution" on Page 1 of
this section.
1 . Raise vehicle on hoist. Remove wheel and brake
drum. It may be necessary to back off the brake shoe
adjustment before the brake drums can be removed. To back
off shoe adjustment, rotate shoe adjusting screw downward.
On JB , JB7 and JB equipped vehicles, it is necessary
6 8
to remove the axle shafts to remove the hub and drum
assembly; refer to Section 4B of this manual.
2. Unhook the primary and secondary shoe return
springs using large pliers.
3. Remove shoe hold down springs.
4. Lift up on actuator, unhook actuating link from
anchor pin, then remove.
5. Spread shoes to clear wheel cylinder connecting
links, remove parking brake strut and spring, disconnect
cable from parking brake lever, remove shoes from the
backing plate.
6 . Separate the brake shoes by removing adjusting-
screw and lock spring. Remove parking brake lever and
secondary brake shoe.
7. Clean all dirt out of brake drum. Inspect drums and
replace or recondition if required.
. Clean all dirt from brake assemblies and inspect for
8
any unusual condition.
9. Wheel cylinders having torn, cut, or heat-cracked
boots should be completely overhauled.
Inspection for leakage may be accomplished at the boot
center hole after removal of link pin. Fluid coatings on
piston within cylinder and on end of link pin removed from
boot are normal, as cylinder contains a porous PISTON
W H ICH IS IM PREGNATED WITH A CORROSION
IN H IB IT IN G FLUID. Fluid spilling from boot center
hole, after link pin is removed, indicates cup leakage and
necessity for completely over-hauling cylinder.
BRAKES 5-37
hole
metal
LIGHT T R U CK SER V IC E MANUAL