GMC 1990 Light Truck Repair Manual page 341

1. Cover
2. Diaphragm
3. Reservoir
4. Grommet
5. Quick Take-Up Valve
6. Spring
7. Spring Retainer
8. Primary Seal
9. Secondary Piston
10. Secondary Seal
11. Snap Ring
12. Primary Piston Assembly
13. Body
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.
5. Secondary piston (28).
• With the rear port plugged apply a small
amount of air pressure to the front port.
6. Secondary seals (29) from the secondary piston (28)
(figure 16).
7. Spring retainer (26) and primary seal (27).
8. Spring (25).
9. Tube seats (if necessary) (figure 17).
• Thread a self-tapping screw into the tube seat
and remove with locking jaw pliers.
Figure 9—Composite Master Cylinder Components
All the metal parts in denatured alcohol.
All the rubber parts in clean brake fluid.
Stained or discolored cylinder bore with crocus
cloth.
L*
Inspect
• Diaphragm for cuts, cracks, or a swollen condition.
• Cylinder bore for scoring or corrosion. If corrosion is
present, replace the cylinder. Do not attempt to hone
the bore.
Install or Connect (Figure 14)
• Lubricate all the seals and cylinder bore with clean
brake fluid.
1. Spring (25).
2. Primary seal (27) and spring retainer (26) onto the
secondary piston (28) (figure 16).
3. Secondary seals (29) onto the secondary piston
(28).
4. Secondary piston (28).
BRAKES 5 -5
F-00769