GMC 1989 Light Duty Truck Repair Manual page 325

R em ove or D isconnect (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 prim ary piston with a smooth
rounded end tool.
6 . Snap ring (52).
7. Primary piston assem bly (51) and piston return
spring (50).
Figure 14— Cast Iron Master Cylinder Components
21. Bail
22. C over
23. D iap hrag m
24. B ody
25. S p rin g
26. S p rin g R e ta in e r
27. P rim a ry Seal
28. S e co n d a ry P isto n
29. S e co n d a ry Seals
30. P rim a ry P isto n A s s e m b ly
31. S nap R ing
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 b o re. A pply low air p ressure 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
a m o u n t of a ir
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
31
F-00774
p re s s u re to th e fro n t