GMC 1990 Light Truck Repair Manual page 343

+ + Remove or Disconnect (Figure 19)
1. Cover (41).
2. Diaphragm (42).
• Drain all the brake fluid from the reservoir.
3. Bolts (54) and reservoir (44).
4. O-ring (55) and compensating valve seals (45).
5. Valve poppets (46) and springs (47).
• Depress the primary piston with a smooth
rounded end tool.
6. Snap ring (52).
7. Primary piston assembly (51) and piston return
spring (50).
Figure 14—Cast Iron Master Cylinder Components
Bail
Cover
Diaphragm
Body
Spring
Spring Retainer
Primary Seal
Secondary Piston
Secondary Seals
Primary Piston Assem bly
Snap Ring
CAUTION: In the following step if air pressure is
used to remove the secondary piston, place the
open end of the cylinder bore approximately 25
mm (1>inch) from a padded workbench or other
surface to catch the piston when it comes out
of the bore. Apply low air pressure very
carefully to ease the piston out of the bore.
Never point the open end of the bore at anyone
when applying air pressure. The piston may
come out of the bore with considerable force
and cause personal injury.
8. Secondary piston assembly (49).
• With the front port plugged, apply a small
am ount of air pressure to the fro n t
compensating valve port.
9. Secondary spring (48).
Clean
• All the metal parts in denatured alcohol.
• All the rubber parts in clean brake fluid.
BRAKES 5-7
F-00774