GMC 4000 Series Service Manual page 198

CAUTION: DO NOT hook the actuating
link over the anchor pin with a regular
spring hook tool. This may damage the
wheel cylinder boot. Place the actuating
link over the anchor pin first and then
fasten link to actuating lever assembly by
holding this assembly in the full "DOW N"
position.
9. Install primary shoe return spring in shoe
and pull over anchor pin. Refer to figure 30.
IMPORTANT: Return spring for primary shoe
is always installed AFTER actuating link, regard­
le s s of right or left, so that it will be in the OUT­
SIDE position on the anchor pin.
10. Install secondary shoe return spring in
shoe and pull over actuating link.
11. Pry shoes away from backing plate and
lubricate shoe contact surfaces with special lubri­
cant (S-17). Be careful to keep lubricant off linings.
Refer to figure 31.
12. Check operation of self-adjusting mech­
anism by hand operating. If there is any binding,
locate trouble and correct. Refer to figure 32.
13. Expand adjustment as far as possible to
still permit brake drums to clear linings. Install
brake drums.
14. Install wheels, lower vehicle to ground
and finish adjustment by applying brakes as many
tim es as required, while vehicle is traveling in
reverse, until proper pedal height is attained.
TYPE "FA" FRONT BRAKE
(Refer to Figure 33)
The type "FA" front brake is the same as the
type "F" brake except for method of adjustment.
The type "FA" brake has an automatic adjusting
mechanism.
An automatic adjuster lever is pivot-pinned
on the inner side of shoe web and rests against the
manual adjuster cam. A drum contact plug is mount­
ed on the pivot pin on the outside of the shoe web
and is centered in the shoe table and lining. A
spring loaded, serrated wedge slides on the pivot
pin and under the drum contact plug between the
plug pin and a wedge guide which is also pinned on
the shoe web. A torsion spring is hooked over the
contact plug pin, the lever pivot pin, and the edge
of the shoe web. This torsion spring holds the a s­
sembly stable and keeps the plug surface flush
with the lining surface.
As the lining wears, the brake drum depresses
the contact plug and it moves the adjuster lever
away from the shoe table. In this gradual action,
the spring loaded wedge moves to keep the gap
between the plug pin and the wedge guide closed.
G M C S E R V I C E M A N U A L
1 Brake Shoe and
2 Contact Plug
3 Backing Plate
4 Brake Shoe Return
5 Wheel Cylinder
This holds the lever (and the brake shoe) in the
adjusted position.
pin bottoms on the inner side of its oversized hole
in the shoe web, stopping automatic adjustment.
BRAKE SHOE REMOVAL
(Refer to Figure 34)
drum assembly as directed in "FRONT HUBS AND
BEARINGS" (SEC. 3D) in this manual.
using brake spring pliers.
washer and another flat washer from each pin and
remove shoes from backing plate.
DISASSEMBLE AUTOMATIC ADJUSTER
(Refer to Figure 34)
move spring.
spring coil off lever pivot pin and slide end of
torsion spring off contact plug pin.
shoe web.
HYDRAULIC BRAKES
6 Torsion Spring
Lining Assembly 7 Wedge
8 Wedge Spring
9 Flat Washer, Spring
Spring
Figure 3 3 — Type "F A " Front Brake Installed
At the point of maximum lining wear, the plug
1. Jack up axle and remove hub and brake
2. Remove both brake shoe return springs,
3. Remove C-washer, flat washer, anti-rattle
1. Unhook wedge spring from wedge and re­
2. Unhook torsion spring from shoe web, work
3. Pull adjuster lever from opposite side of
4. Pull contact plug through shoe table.
5. Lift off retainer washer, wedge, and guide.
Sec. 5A
Page 191
Washer, and "C"
Washer