Chevrolet 70 1969 Series, Shop Manual

Page: 222 / 913

BRA KES 5B-29
1 Air Brake Hose
2 Brake Chamber
3 Mounting Bracket
4 Slack Adjuster
5 Rear Axle
9
10
Snap Ring
Brake
Camshaft
Lubrication Hole Plug
Clevis pin
Adjusting Clevis urn
Figure 7 — Brake Chamber and Slack Adjuster Installed (Rear!
An air brake chamber is used at each wheel
to convert the energy of compressed air into the
mechanical force and motion required to apply the
brakes. The yoke on the brake chamber push rod
connects to a slack adjuster which is mounted on
the brake camshaft. Push rod opening and four
equally spaced holes near clamping flange in non­
pressure plate provide for breathing and drainage.
For illustration of brake chambers installed see
figure 6 (at front axle) and figure 7 (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.
BR AK E C H A M B E R O P E R A T IO N
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,
t h e
brake
s h o e
return springs and
the push rod spring return brake shoes, camshaft,
slack adjuster, push rod, and diaphragm to re­
leased position.
B R A K E C H A M B E R SE R V IC E A B ILIT Y T EST S
t .
Operating Test
Apply brakes and see that the brake chamber
push rods move out promptly without binding. R e ­
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 pressure plate and non­
pressure plate. No leakage is permissible. Hleak­
age is evident, tighten clamp ring bolts.
b. With brakes fully applied, check for leak­
age through the diaphragm by coating the push rod
hole and drain holes in non-pressure plate with
soap suds. No leakage is permissible. If leakage
is evident, replace the diaphragm.
B R A KE C H A M B E R R E P L A C E M E N T
1. Removal
Disconnect air line from brake chamber. D is­
connect push rod yoke from slack adjuster. Remove
nuts from brake chamber mounting studs, then
remove brake chamber assembly.
2. Installation
Install brake chamber on mounting bracket
and secure with stud nuts and lock washers. Con­
nect push rod yoke to slack adjuster. Adjust brakes
as previously directed under "Brake Adjustment."
Apply brakes and make sure push rod is correct
length. Angle formed by push rod and slack ad­
juster should be greater than 90 degrees with
brakes released, and with brakes applied alter
being adjusted, this angle should still be greater
than 90 degrees; in other words, the slack adjuster
should not go "over center” during brake applica­
tion. If necessary, adjust yoke on push rod to ob­
tain this condition. Push rod must not extend through
yoke far enough to interfere with slack, adjuster,
Test as directed under "Serviceability Tests."
M A IN T E N A N C E
It is recommended that all brake chambers be
removed, disassembled, inspected and thoroughly
cleaned at the time that brakes are relined or at
one year periods, whichever occurs first (also
dependent upon, type of operation and operator ex­
perience), Any parts worn, cracked, or deterior­
ated should be replaced,
AIR
TANKS
The number of air tanks used and their mount­
ing locations vary from model to model. (Refer to
figure 9 for typical installation.) On steel tilt cab
models one tank is mounted crossways between
frame side rails behind front bumper and in front
of first frame crossmember. On conventional
models the tanks are mounted along the outside of
the left frame rail, under the cab in the step area.
CHEVROLET S E R K 7 0 8 0 H W V Y DUTY 1RUCK SH O P M A N U A L