GMC T Series 1994 Repair Manual page 287

NOTICE: When fasteners are removed, always reinstall them at the same location from which they were
removed. If a fastener needs to be replaced, use the correct part number fastener for that application. If
the correct part number fastener is not available, a fastener of equal size and strength (or stronger) may
be used. Fasteners that are not reused and those requiring thread locking compound will be called out.
The correct torque value m ust be used when installing fasteners that require it. If the above conditions
are not followed, parts or system damage could result.
SUBJECT
General D escription........................................................................................................................................................5D1-1
Booster A ssem bly........................................................................................................................................................... 5D1-1
Single D iap hrag m ........................................................................................................................................................5D1-1
Dual D iaphragm ........................................................................................................................................................... 5D1-3
Gaging Procedure........................................................................................................................................................... 5D1-7
Special T o o ls .................................................................................................................................................................... 5D1-7
The vacuum booster is either a single or tandem dia­
phragm vacuum suspended unit. During normal opera­
tion, with the brake pedal released, manifold vacuum is
applied to both sides of the diaphragm(s). Applying the
brakes allows air at atmospheric pressure to enter one
side of the diaphragm(s). This pressure difference pro­
vides the power assist.
SINGLE DIAPHRAGM
4*+ Remove or Disconnect (Figures 1 and 2)
Tool Required:
J 23456 Power Brake Booster Disassembly and
Reassembly Tool
1. Boot (1) and silencer (2).
2. Vacuum check valve (3) and grommet (4).
3. Front housing seal (5).
4. Scribe a mark across front and rear housings to aid
in reassembly.
5. Use J 23456 to apply force in a counterclockwise
direction to unlock housings (figure 1).
6. Return spring (9) and power piston group.
7. Power piston bearing (6) from rear housing (7).
8. Reaction body retainer (25).
9. Piston rod (10) and reaction retainer (11).
10. Filter (12) using an awl or similar tool.
11. Power piston and pushrod assembly (16).
SECTION 5D1
VACUUM BOOSTER
CONTENTS
GENERAL DESCRIPTION
BOOSTER ASSEMBLY
Delco Moraine NDH vacuum boosters have a build
date on a small paper label glued to the front housing.
The first digit indicates the plant where it was built, and
the second digit indicates the year (1 means 1991, 2
means 1992, etc.). The last digits indicate the day it
was built (Example: 271 would mean the 271st day of
the production year).
A. Grasp outside edge of diaphragm support (15)
and diaphragm (14).
B. Hold pushrod (19) down against a hard surface.
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