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5-38
.
1977 PONTIAC SERVICE MANUAL
If the brake linings are slightly worn and the drum is
grooved, the drum should be polished with fin emery cloth
but should not be turned. At this stage, eliminating all
grooves in drum and smoothing the ridges on lining would
necessitate removal of too much metal and lining, while if left
alone, the grooves and ridges match and satisfactory service
can be obtained. If brake linings are to be replaced, a grooved
drum should be turned for use with oversize linings. A
grooved drum, if used with new lining, will not only wear the
lining, but will make it difficult, if not impossible to obtain
efficient brake performance.
Out-Of-Round or Tapered Drum
An out-of-round drum makes accurate brake shoe
adjustment impossible and is likely to cause excessive wear
of other parts of brake mechanism due to its eccentric action.
An out-of-round drum can also cause severe and irregular tire
tread wear as well as a pulsating brake pedal. When the
braking surface of a brake drum exceeds the factory
specification limits in taper (and/or) being out-of-round, the
drum should be turned to true up the braking surface. Out-of-
round as well as taper and wear can be accurately measured
with an inside micrometer fitted with proper extension rods.
When measuring a drum for out-of-round, taper and
wear, take measurements at the open and closed edges of
machined surface and at right angles to each other.
Turning Brake Drums
If a drum is to be turned, only enough metal should be
removed to obtain a true, smooth braking surface. If a drum
does not clean-up when turned to a maximum diameter as
shown in the general specification, it must be replaced.
Removal of more metal will affect dissipation of heat and may
cause distortion of the drum.
All brake drums have a maximum diameter cast into
them. This diameter is the maximum wear diameter and not
a refinish diameter. D o no refinish a brake drum that will not
meet the specifications, as shown below, after refinishing.
Brake Drum Balance
During manufacture, brake drums are balanced within
three ounce inches. These weights must not be removed.
After drums are turned, or if difficulty is experienced in
maintaining proper wheel balance, it is recommended that
brake drums be checked for balance. Brake drums may be
checked for balance on most off-the-car balancers.
D R U M DIAMETERS
9.500" Drum
Maximum Rebore
...................................................
9.560"
Discard
................................................................
9.590"
1 1.000" Drum
Maximum Rebore
.................................................
1 1.060"
Discard
................................................................
1 1 .090"
WHEEL BOLT REMOVAL A N D
INSTALLATION
Drum Brakes
1. Remove hub and drum assembly from car
2. Secure hub and drum assembly in a vise and mark
center of the bolt head with a center punch. Drill 1/8" pilot
hole in head of bolt; redrill head using a 9/16" bit. Cut off
any remaining portion of bolthead using a chisel and then
drive out boltwith drift. See Fig. 5-59.
-
TO REMOVE BOLT
SHOULDER RESULTING
DRILL OFF BOLT
FROM SWAGING
HEAD
6
DRIVE
PERATION DURING
OUT BOLT IN
MANUFACTURE
DIRECTION
OF ARROW
*
WHEEL BOLT
1
pJJ: ; ; E : : " u:
4232
Fig.
5-59 Bolt
Pressed
Into
Place
3. Press new wheel bolt into place in drum and reinstall
assembly onto car.
4. Refer to Group 3 for correct wheel bearing
adjustment.
WHEEL CYLINDER OVERHAUL
Removal of Brake Wheel Cylinder
1. Remove wheel, drum and brake shoes. Be careful not
to get grease or dirt on brake lining.
2. Remove wheel cylinder from backing plate.
Disassembly of Brake Wheel Cylinder
1. Inspect cylinder bore for scoring or corrosion. It is
best to replace corroded cylinder.
2. Polish any discolored or stained area with crocus cloth
by revolving cylinder on cloth supported by a finger.
3. Rinse cylinder in clean brake fluid.
4. Shake excessive rinsing fluid from cylinder. D o not
use a rag to dry cylinder, as lint from the rag cannot be kept
from cylinder base surfaces.
Assembly of Brake Wheel Cylinder
1. Lubricate cylinder bore and counterbore with clean
brake fluid and insert spring-expander assembly.
2. Install new cups. (Be sure cups are lint and dirt free).
Do not lubricate cups prior to assembly.
3. Install new Durex pistons.
4. Press new boots into cylinder counterbores by hand.
D o not lubricate boots prior to assembly.
Installation of Brake Wheel Cylinder
1. Install wheel cylinder on brake backing plate and
connect brake pipe or hose. Torque rear wheel brake pipe to
wheel cylinder to 100 lb. in.
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