Chevrolet 70 1969 Series, Shop Manual

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POWER BRAKE 5-16
Figure 1 3 — D isa sse m b lin g H a n d Control V a lv e Piston
perfections may be cleaned up with crocus cloth. If
badly worn, or pitted, replace with new parts.
2. C heck action of piston cup in piston; graduating
spring is under a preload of 14 to 18 pounds, thus
pressure in excess of this must be applied to cup to
check action of cup in piston. If piston or cup is dam ­
aged in any way, or if spring is weakened, disas­
semble piston and replace damaged parts as directed
later under “ Repair.”
3. Inspect bearing plunger and operating cam for evi­
dence of wear and replace if necessary.
Repair (Key Numbers Refer to Fig. 12)
1. Disassemble Piston. Place piston assembly in arbor
press and press piston cup down away from snap ring
as shown in Figure 13. Remove snap ring (9), then re­
lease arbor press. Remove piston cup (8), graduating
spring (6), cup spacers (7), and graduating spring spa­
cers (25) from piston. Discard damaged parts and ob­
tain new parts for assembly.
2. Assem ble Piston.
a. Travel of piston cup (8) between snap ring
(9)
and spacers (7) must be within limits shown on
Figure
19.
T o check travel of cup. install spacers
(7) which were removed, then install piston cup
in piston, without graduating spring, and seat
cup against spacers. M easure distance from top
of cup flange and bottom edge of snap ring
groove as shown in Figure
10.
A d d or remove
spacers (7) as necessary to obtain a dimension
of
0.090
to
0.100
inch.
b. Remove cup from piston, leaving spacers (7) in
place. A p p ly a thin coating of multipurpose grease
(N .L .G .I. number I with a rust inhibitor ingre­
dient) to cup bore in piston. Install graduating
Figure 14 — H a n d C o n tro l Piston, C u p a n d G r a d u a t in g S p r in g
spring spacers (25). graduating spring (6), and
piston cup (8) in piston. Place the assembly in
arbor press and press the piston cup into piston
until cup clears snap ring groove. Install snap
ring (9). Check preload on spring. Add or re­
move spacers (25) if necessary to obtain a pre­
load of 16 pounds, plus or m inus 2 pounds.
HAND CONTROL VALVE ASSEMBLY
Key Numbers in Text Refer to Fig. 12
1. C oat valve guides in valve cage (3) with a m ultipur­
pose grease (N .L .G .I. number 1 with a rust inhibitor
ingredient). Assem ble exhaust valve (27), valve spring
(28), inlet valve (29), and nut (30) in valve cage, with
parts positioned as shown in Figure 12. H old exhaust
valve while firm ly tightening nut.
2. Install O -ring (26) and seal (5) in grooves in piston.
L ip of seal must point toward sm all end of piston.
3. C oat operating cam (15) with a multipurpose grease
Figure 15— M e a s u r in g Piston Travel
CHEVROLET SERIES 70 80 HEAVY DUTY TRUCK SHO P M A N UA L