GMC 4000 Series Service Manual page 196

1 Shoe Guide Plate
2 Anchor Pin
3 Wheel C ylinder
4 P rim ary Shoe Return
Spring
5 Brake Backing Plate
6 Prim ary Brake Shoe
and Lining
7 Hold-Down W asher
8 Hold-Down Pin
9 C onnecting Spring
10 Adjusting Nut
11 A djusting Screw
Figure 2 7 — Duo-Servo Front Brake (Automatic Adjuster)
4. Unhook primary shoe return spring first
from anchor pin and secondary shoe return spring
from actuating link. Refer to figure 28.
5. Remove actuating lever return spring.
6. Disengage actuating link end first from
anchor pin, then from adjusting lever pivot.
7. Remove hold-down pins and springs. Refer
to figure 29.
8. Remove the actuating lever assembly.
NOTE: The actuating lever, adjusting lever
pivot and lever override spring are removed as
an assembly. It is not recommended that they be
disassem bled for service purpose unless one or
more of the components is damaged. It is much
easier to assemble and disassem ble the brakes by
leaving this assembly intact.
9. Remove brake shoe guide plate.
10. Pull top of shoes away from anchor pin
and wheel cylinder push rods and remove shoes
from backing plate.
11. Move top of brake shoes toward one another
crossing them until adjusting screw assembly and
spring fall off, permitting shoes to separate.
CLEANING AND INSPECTION
1. Clean all dirt out of brake drum. Inspect
G M C S E R V I C E M A N U A L
12 A djusting Socket
13 Actuating L ev er
14 L ever Return Spring
15 L ever O verride
Spring
16 Hold-Down Spring
17 Adjusting L ever
Pivot
18 Secondary Brake
Shoe and Lining
19 Actuating Link
20 Secondary Shoe
R eturn Spring
r u n
HYDRAULIC BRAKES
Figure 2 8 — U nhooking Brake Shoe Return Spring
drum for roughness, scoring, or out-of-round.
Replace or recondition drum as necessary. Refer
to "Brake Drums" in this section.
2. Carefully pull lower edge of wheel cylinder
boots away from cylinders and note whether inter­
ior is excessively wet with brake fluid. Excessive
fluid indicates leakage past piston cups, requiring
overhaul of wheel cylinder.
NOTE: A slight amount of fluid is nearly al­
ways present and acts as lubricant for pistons.
3. Check all backing plate attaching bolts to
make sure bolts are tight. Clean all rust and dirt
Figure 2 9 — R e m oving H o ld D o w n Sp rin gs a n d Pins
Sec. 5A
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