2-6
GROUP 2 - Brakes
last. Depress the brake pedal slowly
to build line pressure until the pres-
sure differential valve is moved to a
centralized position and the brake
warning light goes out; then, immedi-
ately tighten the outlet port tube nut.
2.
Check the fluid level in the mas-
ter cylinder reservoirs and fill them to
within 1/4 to 1/2 inch of the top with
the specified brake fluid, if necessary.
3.
Turn the ignition switch to the
OFF position.
4.
Before driving the vehicle, check
the operation of the brakes and be sure
that a firm pedal is obtained.
CLEANING AND INSPECTION
DISC BRAKES
1.
Remove the wheel and tire
and the shoe and lining assemblies
as outlined in Part 2-2, Section 2.
2.
Make thickness measurements
with a micrometer across the thinnest
section of the shoe and lining. If the
assembly has worn to a thickness of
0.230-inch (shoe and lining together)
or 0.030-inch (lining material only)
at any one of three meauring locations
or if lining shows evidence of brake
fluid contamination, replace all (4)
shoe and lining assemblies on both
front wheels.
3.
Check the caliper to spindle at-
taching bolts torque. Torque them to
specification, if required.
4.
To check rotor runout, first
eliminate the wheel bearing end play
by tightening the adjusting nut. After
tightening the nut, check to see that
the rotor can still be rotated.
5.
Clamp a dial indicator to the
caliper housing so that the stylus
contact the rotor at a point approxi-
mately 1 inch from the outer edge.
Rotate the rotor and take an indica-
tor reading. If the reading exceeds
0.002 inch total lateral runout on the
indicator, replace or resurface the disc
brake rotor. The following require-
ment must be met when resurfacing
disc brake rotors:
Rotunda Disc Brake Attachment
FRE-2249-2 is the only approved tool
to be used to refinish the disc brake
rotors.
The step-by-step resurfacing
procedure provided with the tool
must be adhered to.
The finished braking surface of the
rotor must be flat and parallel within
0.0007 inch; lateral runout must not
exceed 0.002 inch total indicator
reading, and the surface finish of the
braking surface are to be 85/15
micro inches. The minimum limiting
dimension (Fig. 8) from the inboard
bearing cup to the inboard rotor face
(dimension B) and the outboard rotor
surface and the inboard bearing cup
(dimension A), must be observed
when removing material from the
rotor braking surfaces.
When the runout check is finished
HI
532-A
FIG.
8—Disc
Brake Rotor Service
Limits.
be sure to adjust the bearings as out-
lined in Group 3, in order to prevent
bearing failure.
6. Check the rotor for scoring.
Minor scores can be removed with a
fine emery cloth. If the rotor is ex-
cessively scored, refinish it as outlined
in step 5 or replace the rotor, if re-
quired.
7.
Visually check the caliper if
excess leakage is evident, it should be
replaced. Slight leakage around the
piston or a seized piston indicates
the need for removal and disas-
sembly.
8. If upon disassembly the caliper
if found to be distorted or damaged,
or if the cylinder bores is scored or
excessively worn, replace the assem-
bly.
9. Check the brake hoses for signs
of cracking, leaks or abrasion. Re-
place them if necessary.
DRUM BRAKES
1.
Remove the wheel from the
drum, and remove the drum as out-
lined in Part 2-2, Section 2.
2.
Brush all dust from the backing
plates and interior of the brake
drums.
3.
Inspect the brake shoes for ex-
cessive lining wear or show damage.
If the lining is worn within 1/32 inch
of the rivet heads or if the shoes are
damaged, they must be replaced. Re-
place any lining that had been con-
taminated with oil, grease or brake
fluid. Replace lining in axle sets.
Prior to replacement of lining, the
drum diameter should be checked to
determine if oversize linings must be
installed.
4.
Check the condition of brake
shoes,
retacting springs, hold-down
springs, and drum for signs of over-
heating. If the shoes have a slight
blue coloring, indicating overheating,
replacement of the retracting and
hold-down springs is strongly recom-
mended. Overheated springs lose their
pull and could cause the new lining
to wear prematurely, if they are not
replaced.
5. If the vehicle has 30,000 or more
miles of operation on the brake lin-
ings or signs of overheating are pres-
ent when relining brakes, the wheel
cylinders should be disassembled and
inspected for wear and entrance of
dirt into the cylinder. The cylinder
cups should be replaced., thus avoid-
ing future problems.
6. Inspect all other brake parts and
replace any that are worn or dam-
aged.
7.
Inspect the brake drum and, if
necessary, refinish. Refer to Part 2-2,
Section 4 for refinishing.
BOOSTER UNIT
Check the booster operation as
noted in Part 2-1, Section 1, Power
Brake Functional Test. If the brake
booster is damaged or defective, re-
place it with a new booster. The
brake booster is serviced only as an
assembly.
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