GMC 4000 Series Service Manual page 216

C O N S T A N T PRESSURE LIN ES
D ELIVERY LINES
1 Slack Adjuster
2 Standard Brake Chamber
3 Limiting and Quick Release
Valve
4 Air Compressor
5 Air Intake
6 Governor
7 Emergency Parking
"Push-Pull" Valve
how this valve works, refer to procedures under
heading of "Moisture Ejector Valve."
The complete air system should be checked
for leakage at regular intervals. Build up air p res­
sure in system to governor cut-out point, then with
engine stopped and brakes released, observe rate
of air pressure drop registered by the dash air
pressure gauge. The rate of drop should not ex­
ceed two pounds per minute. With engine stopped
and brakes fully applied, observe rate of air p res­
sure drop registered by the dash gauge. Rate of
drop should not exceed three pounds per minute.
If leakage is excessive, leakage test should be
made at air line connections and at all air brake
G M C S E R V I C E M A N U A L
8 Trailer Brake Hand
Control Valve
9 Two-Way Valve
10 Low Air Buzzer Switch
11 Air Gauge
12 Application Valve
13 Double Check Valve
14 Tractor Protection Valve
15 Trailer Brake Service Line
Figure 1 — Schematic D iagram of Typical Air Brake System
16 Trailer Brake Emergency
17 Air Tanks
18 Stopmaster Brake
19 Check Valve
20 Moisture Ejector Valve
21 Drain Valve
22 Safety Valve
control units as directed under individual headings
later in this section.
In cold weather, particular attention should be
given to draining of moisture from air system .
BRAKE ADJUSTMENTS
Brake adjustments to compensate for normal
lining wear are made at slack adjuster at each
wheel. Adjustment must be made before the brake
chamber push rod travel reaches the maximum
working stroke listed in "Specifications" at end
of this section.
On 5500 and 6500 "cowl" models, an adjustable
Sec. 5B
Page 209
AIR BRAKES
Line
Chambers
-3469
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