Chevrolet 10 Series 1968, Service Manual, Page: 323 / 713

BRAKES 5-80
Le akage Test
1. With system pressure up and DD3 actuators in the
released position, check drain slot and around the
push rod boot with a soapy solution to detect possible
leakage by the locking piston grommet.
2. Make and hold a service brake application and again
check the actuator drain slot for service diaphragm
leakage. Continue to hold the service application and
coat around the service and auxiliary diaphragm
rings with the soapy solution to detect seal leakage.
3. Operate the actuator control valve to a parking po­
sition and check the exhaust port of a service brake
application to detect auxiliary diaphragm leakage.
This auxiliary diaphragm leakage detection point
could be the exhaust port of the foot brake valve,
quick release valve or relay valve depending on
system. While still in a parking position, the aux­
iliary diaphragm clamping ring should be coated
with the soap solution to detect seal leakage.
4. Should leakage be detected at the clamping rings in
either of the above tests, the clamping ring nuts
should be tightened evenly but only enough to stop
leakage.
5. If the DD3 Safety Actuator does not function as de­
scribed or leakage is excessive, the actuator can be
repaired by following the procedure outlined under
"Service Operations" of this section.
SERVICE OPERATIONS
PUSH-PULL C O N T R O L V A LV E
Removal
1. Block or hold vehicle by some means other than air
brakes.
2. Drain air brake system.
3. Disconnect air lines from control valve.
4. Drive out spiral pin that holds button on control valve
plunger.
5. Remove button and warning ring.
6. Remove control valve mounting nut, then control
valve.
Disassem bly (Fig. 115)
1. Insert a punch or rod in the plunger pin hole to keep
the plunger from turning while removing the nut at
the bottom of the valve.
2. Remove the plunger and spring.
3. Remove the plunger grommet.
4„ Remove the two cover screws and separate the cover
from the body.
5. Remove the cover seal grommet and the inlet and
exhaust valve.
6. Remove the piston, then the piston grommets.
Cleaning and Inspection
1. Wash all metal parts in a good cleaning solvent and
dry. Wipe all reusable rubber parts clean.
2. Inspect all parts for excessive wear or deterioration.
3. Inspect the inside area of the plunger and piston
bores for nicks and burrs.
4. Check springs for cracks, distortion or corrosion.
5. Inspect the grommets and inlet and exhaust valve
for wear and deterioration.
6. Replace all parts not considered serviceable during
these inspections.
Assem bly
NOTE:
Prior to assembly, lubricate all grom­
mets and bearing surfaces of the body and cover
with a Barium-Base Grease.
1. Install grommet on plunger.
2. Position spring on plunger.
3. Insert plunger, with spring and grommet installed,
in body.
4. Position inlet and exhaust valve over protruding end
of the plunger. The double beaded side of the inlet
and exhaust valve should be against the body seat.
Attach the cover to the body with two screws.
Install the piston, with the grommet installed, over
the plunger stem.
Depress the plunger, and with a punch or rod hold
it from turning while installing the plunger stem
nut. Torque on this nut should be between 30 and 40
inch pounds.
F ig . 115-Push Pull Control V a lv e
1. Spiral Pin
2 . Warning Ring
3. Supply Port
4 . Inlet and Exhaust
V a lv e
5. Seal Grommet
6. Exhaust Part
7 . Grommets
8. Button
9. Plunger
10
.
11
.
12
.
13.
Spring
D e livery Port (2)
Piston
Nut
CHEVROLET TRUCK SERVICE MANUAL