Chevrolet 1980 Light Duty Truck Repair Manual page 141

20. W ith Tool J-28458 still positioned on the power
piston, hold the housing divider so that formed over flange
o f the divider faces up. Press the divider down over the tool
and onto the power piston tube where it w ill rest against
the secondary diaphragm (fig. 5-6A).
21. A ssem ble the primary diaphragm to the primary
support plate. Press the raised flange on the I.D . o f the
diaphragm through the center hole o f the support plate. Be
sure that the edge o f the support plate center hole fits into
the groove in the raised flange o f the diaphragm. Lubricate
the diaphragm I.D . w ith silicone lubricant.
22. R em ove Tool J-28458 from power piston.
23. Fold the primary diaphragm away from the O .D .
o f the primary support plate and place the primary support
plate and diaphragm assembly over the power piston and
push down until it bottom s (fig. 5-7A).
24. Fold the primary diaphragm back into position on
the primary support plate and pull the diaphragm O .D . over
the formed flange o f the housing divider. C heck that the
bead on the diaphragm is seated evenly around the com plete
circumference.
25. Place the diaphragm retainer over power piston and
onto diaphragm. Place T ool J-28458 over power piston onto
diaphragm retainer. Strike with hammer until retainer is
locked on neck o f power piston (fig. 5-8A).
26. Install power head silencer over neck o f power
piston until it rests on retainer.
27. Wipe a thin film o f silicone lubricant on the O .D .
o f the piston rod retainer. Insert the master cylinder piston
rod retainer into the cavity in the power piston so that the
flat end bottom s against the rubber reaction disc in the
bottom o f the cavity.
28. Place the power piston bearing in rear housing
center hole so that the formed flange o f the housing center
hole fits into the groove o f the power piston bearing. The
thin lip o f the bearing w ill protrude to the outside o f the
housing.
29. Coat the I.D . o f the power piston bearing with
silicone lubricant.
Final A ssem bly (Fig. 5 -1 OA)
1. M ount T ool J-23456 in vise and position rear
housing in tool. R etain rear housing with tw o nuts.
2. Install the power piston assembly to the rear housing
by pressing the tube o f the power piston through the rear
housing bearing. Press down until the housing divider seats
in the rear housing and the power piston bottom s against
the housing.
3. Install power piston return spring over reaction body
retainer.
4. Lower front housing over rear housing and position
bar on front housing.
Be sure scribe marks are aligned.
5. Tighten down on front housing and fit the tangs in
the appropriate slots on the rear housing.
6. Rotate the bar clockw ise into locked position.
R em ove bar from front housing. Stake housing interlocks
at 2 new locations 180° apart (fig. 5-9A).
Gaging
1. Insert the m aster cylinder piston rod, flat end first,
into the piston rod retainer.
2. Press down on the master cylinder piston rod (with
approxim ately a 40-50 pound load) to be sure it is properly
seated.
3. R em ove the front housing seal to assure that no
vacuum is in the power head w hile gaging.
4. Place G age J-22647 over the piston rod in a position
which w ill allow the gage to be slipped to the left or right
without contacting the studs (fig. 5-11 A).
5. The center section o f the gage has two levels. The
a lw a y s
piston rod should contact the longer section (low er
level) o f the gage. The piston rod should
shorter section (higher level) o f the gage. M ove gage from
side to side to check piston rod height.
6. A ny variation beyond these tw o lim its m ust be
com pensated for by obtaining the service adjustable piston
rod and adjusting the self-locking screw to m eet gaging
specifications.
7. W ipe a thin film o f silicone lubricant on the I.D . o f
the front housing seal and position seal in the depression in
the housing.
8. R em ove power brake unit from T ool J-23456.
9. Place the silencer in the closed end o f the push rod
boot. Push the boot retainer over the boot. Stretch the boot
over the push rod and over the flange in the center o f the
rear housing.
10. Refer to "Power Brake U nit Installation".
BRAKES 5-5
never
contact the
O V E R H A U L M A N U A L