Tandem Diaphragm Vacuum Booster - GMC 1989 Light Duty Truck Repair Manual

Lubricate the inside and outside diameters of
the grommet and front housing seal with a thin
layer of silicone.

TANDEM DIAPHRAGM VACUUM BOOSTER

i- +
R em ove or D isconnect (Figure 25)
Tool Required:
J 23456 Power Brake Booster Disassembly
and Reassembly Fixture
1. Boot ( 1 ) and silencer (2).
2. Vacuum check valve (3) and grommet (4).
3. Front housing seal (7).
• Scribe a mark on the front and rear housings to aid
in assembly.
• Unlock the front and rear housings using J 23456
21
(figure ).
4. Return spring ( 11 ) and power piston group (38) (fig­
ure 26).
5. Primary piston bearing (
6 . Piston rod (12), reaction retainer (13) and power
head silencer (14).
7. Power piston assembly (41) along with the pushrod
(32) (figure 27).
• Grasp the assembly at the outside edge of the
housing divider (19) and diaphragms (16 and
20
).
• Hold with the pushrod (32) down against a
hard surface.
• Use a slight force or impact to dislodge the
diaphragm retainer (15).
8 . Primary diaphragm (16) and primary support plate
(17) from the housing divider (19).
9. Primary diaphragm (16) from the primary support
plate (17).
10. Secondary diaphragm (20) and secondary support
plate (21) from the housing divider (19).
11. Secondary piston bearing (18) from the housing di­
vider (19).
8 ) from the rear housing (9).
Figure 24— G aging th e P iston Rod
11. Front housing seal (5).
12. Silencer (2) and boot (1).
• Gage the piston rod using J 22647 (figure 24). If not
within limits, obtain a service adjustable piston rod.
12. Secondary diaphragm (20) from the secondary sup­
21
port plate ( ).
13. Reaction body retainer (24).
14. Reaction body (25).
15. Reaction disc (22) and reaction piston (23) from the
reaction body (25).
16.
Air valve spring (26) and reaction bumper (27) from
the end of the air valve pushrod (32).
17.
Retaining ring (28) from the air valve pushrod as­
sembly (32).
18.
Air valve pushrod assem bly (32) by inserting a
screwdriver through the pushrod eyelet and pulling
it straight out.
• Considerable force will be required.
19
Filter (29), retainer (30) and O-ring (31) from the air
valve pushrod assembly (32).
Inspect
13
All parts for corrosion, nicks, cracks, cuts, scoring,
distortion or excessive wear. Replace parts as nec­
essary.
Use crocus cloth to polish away minor corrosion of
the housings or diaphragm support.
*2ji
Clean
All parts in clean denatured alcohol.
— Do not immerse the power piston and pushrod
assembly in alcohol.
Dry with unlubricated compressed air.
Install or C onnect (Figure 25)
Tools Required:
J 23456 Power Brake Booster Disassembly
and Reassembly Fixture
BRAKES 5-11
F-05891