GMC 4000 Series Service Manual page 183

Sec. 5A
Page 176
HYDRAULIC BRAKES
and remove bolt attaching connecting tube fitting
to lower cylinder. Remove connecting tube and
fitting assembly.
3. Remove one large and two sm all bolts at­
taching each cylinder to backing plate, then remove
cylinders from backing plate.
Installation
NOTE: The two wheel cylinders mounted on
each brake are identical; however, cylinders on
right- and left-hand brakes have opposite cylinder
castings. Clean mating surfaces of cylinders and
backing plate to insure proper alignment.
1. Place each cylinder on backing plate and
attach with one large and two small bolts and lock
washers.
2. Position wheel cylinder connecting tube and
fittings assembly and attach fitting to lower open­
ing in upper cylinder with inlet connector, using
new copper gasket on both sides of fitting. Attach
fitting to lower opening in lower cylinder with
special bolt, using new copper gasket on both sides
of fitting. Tighten inlet connector and special bolt
firm ly.
3. Install bleeder valve in upper opening in
each cylinder.
4. Install brake shoes as directedunder "Brake
Shoe Installation." Bleed brake system as directed
under "Bleeding Brakes."
DUO-SERVO
Removal
1. Jack up axle and remove wheel, brake
drum, and brake shoes as directed later under
"Brake Shoe Removal."
2. Disconnect metal brake tube from flexible
hose at frame, disconnect hose from frame, then
unscrew hose fitting from wheel cylinder housing.
3. Remove cap screw s and washers attaching
wheel cylinder to backing plate and remove cylin­
der assembly.
Installation
1. Position wheel cylinder on backing plate
and attach with cap screw s and lock washers.
2. Thread brake hose fitting into wheel cylin­
der housing using a new copper gasket on hose
fitting. Insert fitting at other end of hose through
frame and secure with toothed lock washer and nut
or with spring lock, depending upon type used. Con­
nect metal brake tube to hose fitting inside frame
side rail.
3. Install brake shoes as directedunder "Brake
Shoe Installation." Bleed brake system as directed
under "Bleeding Brakes."
G M C S E R V I C E M A N U A L
TYPE "FR-3" AND "FR-3A"
Removal
directed under "Brake Shoe Removal."
inder at inner side of backing plate. Remove wheel
cylinder connecting tube at inner side of backing
plate.
ing each wheel cylinder to backing plate. Remove
wheel cylinders and heat shields, then remove heat
shields from cylinders.
Installation
both right- and left-hand brakes are interchange­
able. Cylinders must be positioned on backing
plate so that the long stroke end of the cylinder
faces the shoe toe (adjustment end of shoe) or the
adjusting slot in backing plate. Make sure mating
surfaces of cylinders, heat shields, and backing
plate are clean to assure proper alignment.
and install on backing plate, and attach each cyl­
inder with two bolts and lock washers.
lower cylinder and to lower opening in upper cyl­
inder. Connect axle brake tube to lower opening in
lower cylinder, and install bleeder valve in upper
opening in upper cylinder.
Shoe Installation." Bleed brake system as directed
under "Bleeding Brakes."
TWIN-ACTION
Removal
directed later under "Brake Shoe Removal."
inder connector at inner side of backing plate. Re­
move brake tube connecting wheel cylinders at
outer side of backing plate. Remove dust shield
from upper end of each cylinder.
taching wheel cylinders to backing plate, then re­
move wheel cylinders and heat shield. Remove
brake line connectors from cylinder housings.
Installation
are not interchangeable. Rearward cylinder has
threaded inlet opening near center of cylinder
bore. Forward cylinder has threaded bleeder valve
opening at extreme outer edge of cylinder bore.
Cylinders must be positioned with connecting tube
openings toward each other.
1. Jack up axle and remove brake shoes as
2. Disconnect axle brake tube from upper cyl­
3. Remove two bolts and lock washers attach­
NOTE: Upper and lower wheel cylinders on
1. Position heat shield on each wheel cylinder
2. Attach connecting tube to upper opening in
3. Install brake shoes as directedunder "Brake
1. Jack up axle and remove brake shoes as
2. Disconnect brake tube from rear wheel cyl­
3. Remove cap screws and lock washers at­
NOTE: Forward and rearward wheel cylinders