Chevrolet 70 1969 Series, Руководство по ремонту

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BRAKES 5B-35
When replacing metal tubing, tubing must be free
of burrs, copper cuttings, and dirt. Blow tubing
out with compressed air. Any of the above men­
tioned particles will destroy sealing seats in air
control units. New tubing must be of the same
size as the old tubing.
Always use a new sleeve when replacing tub­
ing. When tightening tube connector nuts, tighten
to torque listed below to assure an air-tight con­
nection. Overtightening will cause leakage. Apply
S .A .E. #10 lube oil to ball sleeves, tubes, and male
threads, then torque to minimum value and check
for leaks. If leaking, back off tube nut approxi­
mately 1/4-turn and retorque to higher than
minimum value.
Tubing Size
1/4 Inch
3/8 Inch
1/2 Inch
5/8 Inch
Torque Inch-Pounds
30 to 50
30 to 50
90 to 115
100 to 125
F L E X IB L E HO SE
Flexible hose is used at each brake chamber,
between cab and frame, and at trailer connections
where it is impossible to use metal tubing due to
1 Trailer Hose
Couplings
2 Dummy Couplings
3 Brake and Electrical
Lines
Hose Support Springs
Electrical Connections
Tractor Protection
Valve
Figure 1 1— Trailer Brake Connections (Conv. Model Shown)
constant flexing during vehicle operation. Hose
connections should be tested at least every 5,000
miles and tightened or replaced if necessary. Any
hose which is chafed, worn, or kinked should be
replaced.
S E R V IC E A B IL IT Y T E ST S
1. Operating Test
If any trouble symptoms, such as slow brake
application or release, indicates a restricted or
clogged air line, disconnect the suspected tube or
hose at both ends and blow through it to make sure
the passage is clear. Inspect tubing and hose for
partial restriction such as would be caused by
dents or kinks. If such condition is found, tubing
or hose should be replaced.
2. Leakage Test
With air system fully charged and brake ap­
plied, coat all tubing and hose connections with
soap suds to check for leakage. No leakage is per­
missible. Leakage is sometimes corrected by
tightening the connection. If this fails to correct
leakage, new fittings, metal tubing, or flexible
hose must be installed.
T R A I L E R C O N N E C T IO N S
On vehicles equipped with trailer connections,
two air lines are used to connect the truck brake
system to the trailer brake system. One of these
lines is the "Service" line and the other is the
"Em ergency" line. The emergency line delivers
constant air pressure to the trailer air tank and
operating valve, while the service line delivers
air pressure to trailer brakes only while the
trailer brakes are being operated, either by means
of the foot brake system or by the trailer brake
hand control valve. Flexible hoses are used to
make the connection between the truck and the
trailer. Each hose is equipped with couplings for
convenience in connecting and disconnecting the
truck and trailer brake systems (see fig. 12).
The emergency line is at the right side and is
tagged "Em ergency." The service line is at the
left side and is tagged "Service." When coupling
tractor and trailer make sure that air lines are
properly connected. Couplings on trailer are also
tagged "Service" and "Em ergency.” See figure 11
for illustration of trailer connections mounted on
the back of a conventional cab model.
1. Couplings
Figure 12 shows a sectional view of a single
hose coupling, and a view of the two couplings con­
nected. The design of the coupling is such that
when the two are connected together, pressure is
placed on two rubber gaskets, making an airtight
seal. The rubber gaskets should be replaced every
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L