Chevrolet 10 Series 1968, Руководство по обслуживанию

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BRAKES 5-74
2. Move the handle to several positions between fully
released and fully applied and note that pressure
registered on the test gauge varies in accordance
with the position of the handle.
Leakage Tests
1. Coat the exhaust port with soap suds with operating
handle in fully released position to check for leakage.
Leakage in excess of a 1-inch bubble in one second is
not permissible. Leakage evidenced by this test is
probably caused by a worn or deteriorated inlet valve
seal, or binding or corrosion between the valves and
valve guides in valve cage, preventing the inlet valve
from fully closing.
2. With operating lever in fully applied position coat
exhaust port with soap suds. Leakage evidenced by
this test may be due to a worn or deteriorated ex­
haust valve seal or by leaking piston seals.
DOUBLE CHECK VALVE
Operating Tests
1. Apply truck brakes and note that the brakes apply
promptly on both the truck and the trailer. Release
truck brakes and note that brakes on truck and
trailer both release promptly.
2. Move hand control valve lever to applied position
and note that brakes apply only on the trailer. Move
control valve lever to released position and note that
trailer brakes release promptly.
Leakage Tests
1. Apply truck brakes and check for leakage at hand
control valve exhaust port, using soap suds.
2. Apply trailer brakes only with hand control valve
and check for leakage at truck brake application
valve exhaust port, using soap suds.
3. Leakage of a one inch bubble in one second is per­
missible in either of these tests. If leakage exceeds
this specification, replace the shuttle valve.
EMERGENCY AIR VALVE AND
BREAKAWAY VALVE
Operating Tests
1. Pull out emergency air valve knob to exhaust air
pressure from breakaway valve control line. Dis­
connect trailer emergency line from emergency out­
let port at breakaway valve and connect an air
pressure test gauge to emergency outlet port.
2. Start engine and build up air pressure in system.
Low air pressure buzzer should stop operating at
approximately 60 psi. With air pressure in operat­
ing range, push emergency air valve knob in. Test
gauge should show full air system pressure. Then
pull knob out; test gauge should drop to zero.
3. Again build up air pressure in system to operating
range, then stop engine. Push emergency air valve
knob in. Make a series of brake applications until
low air buzzer sounds. Slightly open drain cock in
the dry air tank to obtain a slow (approx. 10 psi per
minute) pressure drop in the tractor brake system.
When truck air system drops to 45 psi (approx.) the
emergency air valve knob should automatically come
out and pressure on test gauge should rapidly drop
to zero.
Leakage Tests
1. Build up air pressure in truck brake system to oper­
ating range. Push in emergency air valve knob to
charge trailer brake system. Use soap suds to coat
exhaust ports of emergency air valve and breakaway
valve.
2. When emergency air valve leaks excessively, install
new piston O-rings. When breakaway valve leaks
excessively, install new O-rings and plunger seal.
SERVICE OPERATIONS
HAND CONTROL VALVE
Rem oval
1. Exhaust air pressure from system.
2. Disconnect air lines from valve.
3. Remove bolts and washers securing valve bracket.
4. If valve is to be replaced with a new unit, remove
lock nut and 2nd control lever for installation on re­
placement unit. Remove air line connector fittings
for installation on replacement unit.
Disassem bly
1. Remove cover screw, name plate and cover.
2. Loosen nut and remove operating lever.
3. Scribe marks on valve body and cam housing to per­
mit proper reassembly.
4. Unscrew and remove housing collar.
5. Remove cam housing assembly, camshaft and cam.
Separate the individual parts.
6. Remove adjusting bearing from cam housing.
7. Remove piston spring from body.
8. Remove piston and piston cup from body. Remove
cup from piston.
9. Remove piston return spring from body.
10. Remove end cap and seal from body. Remove seal
from end cap.
11 „ Remove nut from inlet and valve spring retainer.
Remove valve disc.
12. Remove valve spring retainer from body.
13. Remove discharge valve spring from body.
C leaning and Inspection
1. Clean all metal parts in mineral spirits. Make sure
all passages in valve body are open and clean.
2. Inspect internal bores in valve body and external
surfaces of piston which have sliding contact with
each other for evidence of wear, scoring, or cor­
rosion.
3. Inspect all metal parts for wear and deterioration
and replace if necessary. Replace all rubber parts.
CHEVROLET TRUCK SERVICE MANUAL