Chevrolet 1973 Overhaul Manual page 139

5 -3 6 BRAKES
8. Carefully insert hydraulic piston assembly, retainer,
seal and bearing in cylinder bore. Press against
diaphragm and plate to compress return spring and
seat stop washer against bearing inside bore and
then, using snap ring pliers, install snap ring (2)
securely in groove in cylinder bore.
Make sure snap ring is seated all the way
WARNING:
around its groove before releasing pressure against
return spring.
Control Valve (Fig. 5E)
1. Assemble cup (4) facing up on control valve piston
(5), as shown. If two cups are used, install them on
piston back to back. Then assemble piston, washer
(6) and diaphragm (7) and seat inner bead of
diaphragm in piston groove.
2. Lay piston and diaphragm assembly aside.
Assemble poppet return spring (11), vacuum poppet
(10) and atmospheric poppet (14) in valve body (12)
from opposite sides, as shown.
3. Snap poppet retainer (15) over end of vacuum
poppet stem. Set valve body with vacuum poppet
down on 1" wooden cube and tap retainer with soft
hammer until it snaps onto stem of vacuum poppet.
4. Assemble cover (16) securely in groove of valve
body. Assemble spring retainer washer (8) and
spring (9) on end of control valve piston, from end
shown. Insert control valve piston, diaphragm and
spring assembly in valve body with spring around
bosses.
5. Press outer bead of diaphragm into valve body
groove and, while holding spring compressed, dip
piston and cup(s) in clean brake fluid.
6. Align valve body to scribe marks and assemble
control valve piston carefully in its bore below
hydraulic cylinder bore. Secure valve body with
four capscrews (13).
7. Tighten screws to 40-60 in. lbs. Install fitting and
gasket (2) on end of hydraulic cylinder and tighten
fitting to 50-85 ft. lbs. If removed, install bleed
screw and tighten to 10-15 ft. lbs.
Rear Shell, Control Tube, Hose (Fig. 2E)
1. Coat bead of diaphragm or flanges of front and
rear shells with talcum powder or Delco Silicone
Lube #5459912 (or equivalent) and place rear shell
(6) on diaphragm.
2. Align scribe marks on both shells. Make certain
bead of diaphragm is seated in outer flanges of
both shells and hold rear shell in position while
assembling clamp band (8) over flanges of shells
and bead of diaphragm. Position opening in band
45 degrees off vertical center line of Hydrovac on
side away from mounting bracket.
3. Squeeze ends of band together and assemble bolt
(9) and nut (7). Tap band lightly with soft hammer
while tightening bolt to seat band securely on shells.
After tapping, re-tighten to 40-60 in. lbs.
4. Place new seal (2) on control tube (3), as shown,
and assemble hose (4) to tube (5) of rear shell and
to control tube. Attach tube and nut (3) to control
valve body port. Securely tighten to 7-10 ft. lbs.
OVERHAUL MANUAL