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5-46
1977 PONTIAC SERVICE MANUAL
DISASSEMBLY OF BENDIX TANDEM
POWER BRAKE UNlT
Disassembly of Overall Unit
1. Scribe a line across front and rear housings to facilitate
reassembly.
2. Carefully remove hydraulic push rod and seal and
slide seal from rod.
3. Remove vacuum check valve and grommet, if
required.
4. Remove dust boot and silencer from operating valve
rod.
5. Remove dust guard retainer, dust guard and silencers
from rear plate hub with an awl. Then, reinstall steel retainer
on hub.
6. Squirt alcohol down operating valve rod to lubricate
rubber grommet in the valve plunger.
7. Position two small blocks of wood on either side of
air valve rod and install end of air valve rod in vise, leaving
just enough clearance to position two (2) open end wrenches
between vise and retainer on hub of rear plate.
8. Using the wrench nearest the vise as a pry, force the
valve plunger grommet off from the ball end of the rod. Do
not damage plastic hub or allow vacuum cylinder to fall to
the floor. See Figures 5-74 and 5-75.
Fig. 5-74 Removing Air Valve Rod
9. The edge of the rear shell contains twelve (12) lances.
Four (4) of these lances (one in each quadrant) are deeper
than the other lances. The metal that forms the four (4) deep
lances must be partially straightened so that the lances will
clear the cutouts in the front shell. If the metal tabs that form
the lances break during straightening, the shell must be
replaced. See Fig. 5-76.
10. Remove the hydraulic push rod and vacuum seal
from the front shell.
1 1. Mount Tool J 23456 in a vise, and position the power
section on the tool so that the four (4) studs on the rear shell
fit into holes in the tool. See Fig. 5-77.
12. Position the handle over the two (2) studs on the
front shell and tighten the screw to apply a downward
pressure on the front shell. Then, rotate the wrench and front
shell counterclockwise until the lances in the edge of the rear
shell are aligned with cutouts in the front shell. Considerable
effort may be required to rotate the front shell.
13. Slowly release the screw of the tool to permit the two
(2) shells to separate.
WARNING: THE DIAPHRAGM RETURN
SPRING
IS
COMPRESSED
IN
THE
POWER SECTION AND EXPANDS AS
THE PRESSURE ON THE SHELLS IS
REMOVED. IF THE SHELLS DO NOT
SPEARATE WHEN THE SCREW HAS
BEEN TURNED SLIGHTLY TO REDUCE
THE PRESSURE, TAP THE SHELLS WITH
A RUBBER HAMMER TO BREAK THE
BOND.
14. Continue to release the screw until diaphragm spring
tension has been removed.
15. Remove the front shell and return spring.
16. Work edges of front diaphragm from under lances
of rear housing and remove complete vacuum assembly from
rear housing, using care not to damage rear housing seal.
Bosses on center plate must be aligned with cutouts in rear
housing to remove the assembly.
17. Wet the rear diaphragm retainer with alcohol and
remove the retainer using fingers only.
18. Clamp Tool J 22839 in a vise. Place the diaphragm
and plate assembly on the tool with the tool seated in the hex
opening in the front plate.
19. Twist the rear diaphragm plate counterclockwise,
using hand leverage on the outer edge of the plate. It may
be necessary to use a 1" x 1-3/16" x 8" wood strip as a lever
in cover slot on outside circumference of rear plate.
20. After the two (2) plates have been loosened, remove
the plates from Tool J 22839 and place on a bench with the
front plate down. Unscrew the rear plate completely and
carefully lift it off the front plate hub, grasping the valve
plunger and valve return spring as the parts are separated.
See Fig. 5-78.
21. Remove the square section "0"-ring from the
shoulder of the front diaphragm plate hub.
22. Remove the reaction disc from inside the front
diaphragm plate hub. Carefully slide the center plate off the
hub of the front plate.
23. Remove the diaphragms from the plates.
24. If rear housing seal requires replacement, use a blunt
punch or 1-1/4" socket to drive seal from housing. See
Figures 5-79 and 5-80.
CLEANING AND INSPECTION BENDIX
TANDEM POWER BRAKE UNlT
Power Section
All parts to be reused should be washed in alcohol or
brake fluid. Dry the parts with compressed air and place them
on clean paper or lintfree cloth.
Small rust spots inside the shells may be removed with
crocus cloth or fine emery cloth. Be sure to clean thoroughly
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