GMC 4000 Series Service Manual page 200

plug. This can be done with a file, taking care to
not create a "flat spot" on the lining. (An alternate
method is to block adjuster lever in extended posi­
tion and grind plug with lining.) If fully extended
plug is more than 0.005" BELOW lining surface,
replace with new plug.
BRAKE SHOE INSTALLATION
1. Place brake shoes over hold-down pins on
backing place and install a flat washer, an anti­
rattle washer, a flat washer, and a C-washer (in
that order) on each pin. Note that each shoe has a
"heel" and "toe." The "heel" fits in the anchor slot
of wheel cylinder, the "toe" fits in the piston end
of wheel cylinder.
2. After installing both shoes on backing plate,
install return springs. To install each spring,
place spring end with short hook in "toe" of shoe,
then using brake spring p liers, stretch spring and
secure long hook end in ,T heel" of opposite shoe.
3. Center each shoe, before installing drum,
by sliding shoe up or down in its anchor slot until
the leading and trailing edges of the lining are equi­
distant from the inner curl of the brake mounting
plate.
4. Back off manual adjustment cam.
5. Install hub and brake drum as directed in
"FRONT HUBS AND BEARINGS" (SEC. 3D) in this
manual.
INITIAL MANUAL LINING ADJUSTMENT
1. Rotate adjuster cam stud in the direction
of forward drum rotation. Tighten adjustment until
the lining drags on the brake drum.
2. Back off the adjuster cam stud while ro­
tating drum forward, until drag is just relieved.
3. Adjust the second manual shoe adjuster
cam stud in the same manner, forward to tighten
and reverse to relieve drag, and permit automatic
adjustment to take over.
TYPE "FR-3" REAR BRAKE
(Refer to Figure 35)
Each brake is equipped with two double-end
wheel cylinders which apply hydraulic pressure
to both the toe and the heel of two identical, self-
centering shoes. The shoes anchor at either toe
or heel, depending upon the direction of drum ro­
tation. Brake anchor supports and backing plate
are bolted to the axle housing flange. The supports
have removable slotted anchor pins at the shoe
heels, and adjusting screw s at the shoe toes. Ad­
justing screw s act as anchors in the reverse direc­
tion of rotation. Each adjusting screw is threaded
into or out of its support by means of an adjusting
wheel. Adjusting wheels are accessible through
adjusting slots in the backing plate.
G M C S E R V I C E M A N U A L
2 Upper Wheel Cylinder
4 Return Spring (Short)
6 Guide Bolt
7 Guide Bolt Nut Lock
BRAKE SHOE REMOVAL
drum assembly as directed in "REAR HUBS AND
BEARINGS" (SEC. 4C) of this manual.
in cylinders.
remove brake shoe return springs.
from brake shoe guide bolts, then remove brake
shoe assem blies.
lock springs to anchor supports. Thread each ad­
justing screw from the shoe side of its anchor
support by turning adjusting wheels, then lift ad­
justing wheels out of slots in anchor supports.
CLEANING AND INSPECTION
drum for roughness, scoring, or out-of-round.
Recondition or replace drum as necessary. Refer
to "Brake Drums" in this section.
adjusting screw openings in anchor supports.
directed in "REAR HUBS AND BEARINGS" (SEC.
4C) of this manual.
HYDRAULIC BRAKES
1 Wheel Cylinder Heat
Shield
3 Anchor Pin
10 Adjusting Wheel
5 Guide Washer
11 Adjusting Wheel
12 Lower Wheel
Wire
13 Backing Plate
Figure 3 5 — Type "FR-3" Rear Brake Assem bly
1. Jack up axle and remove hub and brake
2. Install wheel cylinder clamps to hold piston
3. Using special brake spring tool (J-8049),
4. Remove lock w ires, nuts, and washers
5. Remove screw s attaching adjusting wheel
1. Clean all dirt out of brake drum. Inspect
2. Clean all dirt out of anchor pin holes and
3. Inspect wheel bearings and oil seals as
4. Inspect brake shoe return springs. If broken,
Sec. 5A
Page 193
8 Brake Shoe and
Lining Assembly
9 Return Spring (Long)
Lock Spring
Cylinder
TPM-9116