Chevrolet 30 Series 1967 Service Manual page 260

BRAKES 5-46
Fig. 75—Installing Retainer Using Bushing Retainer
Socket Tool J -22657
VACUUM BOOSTER POWER BRAKE UNIT
Two Midland-Ross vacuum power booster brake units
(a single and a tandem diaphragm), are used in 1967.
Both types are installed between the master cylinder and
the wheel cylinders in series in the hydraulic circuit, and
use vacuum operated diaphragms to boost the brake pres­
sure delivered to the wheel cylinders. Both units are
frame mounted. Refer to Figure 76.
The tandem diaphragm unit is used with single master
BLEEDING THE SYSTEM
Pressure Bleeding
If using a pressure bleeder, do not allow the air pres­
sure to exceed 25 pounds.
1. Check brake fluid in master cylinder and fill.
2. Open power cylinder bleeder screw and allow fluid
to run until free of air bubbles.
3. Bleed all wheel cylinders until free of air bubbles.
IMPORTANT: Do not apply brakes while en­
gine is running or booster unit may be damaged.
GENERAL DESCRIPTION
MAINTENANCE AND ADJUSTMENTS
. Place snap ring (25), washer (24), and spring (23)
8
over neck of push rod.
9. Push spring down on rod and engage push rod neck
into valve body.
10. Place spring (23) on valve body (22).
11. Place valve body (22) in piston (20) and push snap
ring (25) into place using snap ring pliers.
12. Install new push rod cup (19) in piston (20) with
lip facing end of piston.
13. Slide entire assembly into master cylinder body.
14. Push bushing (15) down push rod until washer (18)
hits stop inside main cylinder.
15. Screw retainer (14) into master cylinder body and
tighten using bushing retainer socket Tool J-22657
(fig. 75). Refer to torque specifications at rear of
manual for correct torque valve.
16. Install lock ring (13) into end of body.
"O "
17. Replace ring seal (27).
18. Install spring (12) and retainer (9).
19. Install snap ring (10).
Installation (Fig. 1)
1. Install main cylinder on power booster.
2. Remove protective material from hydraulic line and
connect line to cylinder. Connect vacuum hose to
manifold.
3. Fill main cylinder to within 1/4 inch of top of
reservoir.
4. Bleed brakes as outlined in this section.
5. Place rubber diaphragm in position on top of main
cylinder.
. Place cover in position and secure with screw. Refer
6
to torque specifications at rear of manual for correct
torque value.
cylinder applications and supplies pressure increased to
all wheels.
The single diaphragm units are used on Van type ve­
hicles with the split brake system. Two units are used
on the vehicle, each one boosting the p ^ ss u re in half of
the split system. Figure 77 illustrates a typical applica­
tion on the Van type vehicle.
4. Apply brakes and check all lines for leaks.
5. Rebleed booster unit with engine running.
Manual Bleeding
Manual bleeding is sim ilar to pressure bleeding except
that the brake fluid is forced through the lines by pumping
the brake pedal instead of the air pressure. An assistant
is required to pump the brake pedal.
1. Start engine and pump brake pedal three times or
until greatest pedal height is obtained—maintain foot
pedal pressure.
CHEVROLET TRUCK SERVICE M ANUAL