Chevrolet 10 Series 1968, Service Manual

Page: 302 / 713

BRAKES 5-59
Inspection
It is of the utmost importance that the compressor is
taking in clean air. The air strainer must be properly
installed and kept clean. If the compressor intake is
connected to the engine air cleaner, etc., these connec­
tions must be properly installed and maintained.
Check compressor mountings to be sure they are se­
cure. Check drive for proper alignment, belt tension,
etc. Inspect oil supply and return lines. Be sure these
lines are properly installed and that the compressor is
getting the proper supply of oil, and just as important,
that the oil is returning to the engine properly.
Check water lines to and from compressor if a water-
cooled type.
If the compressor is air-cooled, check to be sure the
engine fan blast is flowing by the compressor unre­
stricted.
Check unloader mechanism for operation.
Tests (Air Leakage)
Leakage past the discharge valves can be detected by
removing the discharge line, applying shop air back
through the discharge port and listening for escaping air.
Also the discharge valves and the unloader pistons can
be checked for leakage by building up the air system until
the governor cuts out, then stopping the engine. With the
engine stopped, carefully listen for escaping air at the in­
take. To pin-point leakage if noted, squirt soapy water
around the loader pistons. If there is no noticeable leak­
age at the unloader pistons, the discharge valves may be
leaking.
If the compressor does not function as described above,
or leakage is excessive, the compressor should be re ­
paired with genuine service parts, in which case the fo l­
lowing information should prove helpful.
GOVERNOR
Every Six Months or 15,000 Miles:
Remove both governor air filters and wash thoroughly
in cleaning solvent that is known to have no detrimental
effect on metal, nylon, or rubber material.
BRAKE VALVE
Every Year or 50,000 Miles:
Disassemble brake valve and clean all parts. Install
new inlet valves and piston seal.
RELAY VALVE
If the relay valve does not function as described under
Service Checks--Relay Valve (but in any event once each
year) disassemble the valve and clean all rubber parts
and parts subject to wear should be replaced if worn or
damaged. Strainers at relay diaphragm bleeder passage
and exhaust port should be cleaned or replaced.
QUICK RELEASE VALVE
Every Year or 50,000 Miles
Disassemble valve, clean all parts and replace the
diaphragm.
BRAKE CHAMBERS
Every Month or 2,000 Miles:
Check travel of brake chamber push rods and adjust
brakes if necessary. Push rod travel should be kept at
the minimum without brakes dragging.
Excessive travel shortens the service life of brake
chamber diaphragms and also results in slow braking
response.
Every Year or 50,000 Miles:
Disassemble brake chambers and clean all parts. In­
stall new diaphragms. When replacing release springs
be sure to use the correct spring, otherwise uneven
braking will result.
SLACK ADJUSTERS
The slack adjusters for 1967 are fully packed with
grease when assembled and need no periodic lubrication.
If the slack adjuster is disassembled for any reason it
must be repacked with grease in the following way:
1. Remove one plug from the slack adjuster side plate.
2. Using a pressure grease gun, inject grease into the
hole in side cover while turning the worm shaft ap­
proximately 50 revolutions in one direction.
3. Install side plate plug securely.
4. Rotate wormshaft about 3 revolutions in the opposite
direction.
5. Refer to Section 0 - Lubrication for additional in­
formation.
RESERVOIRS
Drain air reservoirs regularly, as required. Local
conditions govern frequency; in dry climates, for ex­
ample, once a month may be sufficient, while in humid
areas it may be necessary to drain reservoirs daily.
Satisfactory draining is accomplished only by leaving
the drain cock open after the air has escaped and until
all drainage stops.
Many an efficient reservoir arrangement has failed in
its normal function through haphazard maintenance.
DRAIN COCKS
All drain cocks should be periodically checked for
leakage, both for leakage past the key and leakage through
the body around the key. Leakage of more than a one inch
soap bubble in one second is not permissible.
SAFETY VALVE
Every Year or 50,000 Miles:
The safety valve should be removed, disassembled and
thoroughly cleaned. Adjust to 150 psi blow-off pressure
after reassembly.
SINGLE CHECK VALVE
Every Year or 50,000 Miles:
The check valve should be dismantled and thoroughly
cleaned.
CHEVROLET TRUCK SERVICE MANUAL