GMC 1990 Light Truck Repair Manual page 348

5-12 BRAKES
Boot
S ile n c e r
Va cu u m C h e c k Valve
3.
Gro m m e t
7. Front H o u s in g Seal
Prim ary P isto n Bearing
Rear H o u s in g
9.
Front H o u s in g
Return Spring
Pisto n Rod (Gaged)
R e a c tio n Retainer
Power Head S ile n c e r
Diaphragm Retainer
Prim ary Diaphragm
Prim ary S u ppo rt Plate
S e c o n d a ry P isto n Bearing
H o u s in g Divider
S e c o n d a ry Diaphragm
20
.
S e c o n d a ry S u ppo rt Plate
21
.
22 R e a c tio n D isc
.
R ea c tio n P iston
23.
R ea c tio n B o d y Retainer
R ea c tio n Body
26. A ir Valve Spring
R ea c tio n B u m p e r
27.
R etain ing Ring
28.
29. Filter
30. Retainer
31. O-Ring
32. A ir Valve Pu sh Rod A s s e m b ly
33. Power P isto n
J 28458 Power Piston Seal Protector
J 37839 Pushrod Height Gage
1. Lubricated O-ring (31) onto the air valve pushrod as­
sembly (32).
2. Air valve pushrod assembly (32) into the power pis­
ton (41).
3. Retainer (30) and seat.
4. Filter (29) over the pushrod eyelet and into the
power piston (41) (figure 27).
5. Retaining ring (28) onto the air valve pushrod as­
sembly (32).
6. Reaction bumper (27) and air valve spring (26).
7. Reaction piston (23) and reaction disc (22) into the
reaction body (25).
8. Reaction body (25).
9. Reaction body retainer (24).
• Lubricate the inside diameter of the secondary dia­
phragm (20) lip, inside diameter of the primary dia­
phragm (16) lip and the secondary piston bearing
(18) with a thin layer of silicone grease.
10. Secondary diaphragm (20) into the secondary sup­
port plate (21).
Figure 25—Tandem Vacuum Booster Components
11. Secondary diaphragm (20) and support plate (21)
over the power piston assembly (41) and pushrod
(32) (figure 28).
• Use J 28458 as a guide to protect the power
piston.
12. Secondary piston bearing (18) into the housing di­
vider (19) with the flat surface of the bearing on the
same side as the six raised lugs on the divider.
13. Secondary piston bearing (18) and housing divider
(19) over the power piston assembly (41) and
pushrod (32). Use J 28458 as a guide (figure 29).
14. Primary diaphragm (16) into the primary support
plate (17).
• Fold the primary diaphragm (16) up, away from the
primary support plate (17).
15. Primary diaphragm (16) and support plate (17) over
the power piston assembly (41) and pushrod (32).
• Fold the primary diaphragm (16) back into position
and pull the outside edge of the diaphragm over the
formed flange of the housing divider (19).
F-05892