GMC 4000 Series Service Manual page 221

Sec. 5B
Page 214
AIR BRAKES
equally spaced holes near clamping flange in non­
pressure plate provide for breathing and drainage.
For illustration of brake chambers installed see
figure 8 (at front axle) and figure 9 (at rear axle).
Brake chambers have two different type clamp
rings; (1) a two-piece ring with two bolts and (2)
a one-piece clamp ring with two bolts at the clamp
ring joint.
BRAKE CHAMBER OPERATION
As air pressure enters the brake chamber
behind the diaphragm, the diaphragm forces push
rod outward, thus applying force to the slack ad­
juster which rotates brake camshaft, applying
brakes. When air pressure is released from the
brake chamber, the brake shoe return springs and
the push rod spring return brake shoes, camshaft,
slack adjuster, push rod, and diaphragm to re­
leased position.
BRAKE CHAMBER
SERVICEABILITY TESTS
1. Operating Test
Apply brakes and see that the brake chamber
push rods move out promptly without binding. Re­
lease brakes and see that they return to released
position without binding.
2. Leakage Test
a. While full brake pressure is being deliver­
ed apply soap suds to clamp ring holding the dia­
phragm in place between the pressure plate and
non-pressure plate. No leakage is perm issible. If
leakage is evident, tighten clamp ring bolts.
b. With the brakes fully applied, check for
leakage through the diaphragm by coating the push
rod hole and drain holes in non-pressure plate
with soap suds. No leakage is perm issible. If leak­
age is evident, replace the diaphragm.
BRAKE CHAMBER REPLACEMENT
1. Removal
Disconnect the air line from brake chamber.
Disconnect push rod yoke from slack adjuster.
Remove nuts from brake chamber mounting studs,
then remove brake chamber assembly.
2. Installation
Install the brake chamber on mounting bracket
and secure with stud nuts and lock washers. Con­
nect push rod yoke to slack adjuster. Adjust the
brakes as previously directed under "Brake Ad­
justments." Apply brakes and make sure push rod
is correct length. Angle formed by push rod and
slack adjuster should be greater than 90 degrees
with brakes released, and with brakes applied
G M C S E R V I C E M A N U A L
after being adjusted, this angle should still be
greater than 90 degrees; in other words, the slack
adjuster should not go "over center" during brake
application. If necessary, adjust yoke on push rod
to obtain this condition. Push rod must not extend
through yoke far enough to interfere with slack
adjuster. Test brake chamber as directed under
"Serviceability Tests."
MAINTENANCE
removed, disassembled, inspected and thoroughly
cleaned at the time that brakes are relined or at
one year periods, whichever occurs first (also de­
pendent upon the type of operation and operator
experience). Any parts worn, cracked, or deter­
iorated should be replaced.
ing locations vary from model to model. On tilt
cab models one tank is mounted crossways between
frame side rails behind front bumper and in front
of first frame crossmember. On conventional cab
models the tanks are mounted along the outside of
the left frame rail, under the cab in the step area.
On "cowl" models the air tank is mounted on the
outside of the left-hand frame side rail near the
front of the vehicle. Standard air tank on all models
except tilt cab is a divided tank which incorporates
a wet tank and a dry tank in the same assembly,
divided by a check valve which is built into the tank.
place to store compressed air so there will always
be an ample supply available for immediate oper­
ation of the brakes. Tanks provide storage for
sufficient compressed air for several brake ap­
plications with engine stopped.
a place where the air, heated during compression,
can cool and the water vapor can condense. Most
of this condensation takes place in the "wet" tank;
this is the tank into which the compressed air is
first discharged from the com pressor. Condens­
ation should be drained from all air tanks daily.
To drain tanks properly, leave drain cocks open
until all air escapes and draining stops. Daily
draining is not necessary on those models which
have the optional moisture ejector valve.
air compressor governor is taken from the dry
tank. A one-way check valve at inlet to second tank
prevents loss of air pressure from the second tank
in the event of leakage in the first tank or air com­
p ressor discharge line.
It is recommended that all brake chambers be
AIR TANKS
The number of air tanks used and their mount­
The purpose of the air tanks is to provide a
Another purpose of the air tanks is to provide
All pressure for operation of the brakes and
Air tank U-bolts and support brackets to frame