Chevrolet 10 Series 1970 Service Manual page 243

WHEEL CYLINDERS (Fig. 7 and 8)
W h eel cylin d ers are identified with type of brake with
which they are used. On D uo-Servo brakes, wheel cylin ­
d er housing construction
how ever intern al construction is the sam e as illustrated.
On D uo-Servo brakes one w heel cylin d er is used at
each brake, mounted on the flange plate between upper
ends of brake shoes as shown in F igu re 2. On Tw inplex
and W agner, " F " , " F A " . " F R -3 "
brakes, two cylin d ers are used at each brake, mounted
on the flange plate between shoe ends as shown in F igu res
3, 4, 5 and 6.
A b leed er va lve fo r purging a ir fro m the hydraulic
system is p rovided on a ll w heel cylin d ers.
p lex brake installation a b leed er va lv e is used only on
the upper cylin der of the two used on each wheel.
BRAKE LININGS
Brake linings on all 10 s e r ie s m odels are attached to
the brake shoes with a sp ecia l brake bonding p rocess.
Only fa c to ry bonded shoe and lining assem b lies should be
used fo r replacem ent. On 20 through 60 s e r ie s m odels,
linings are riveted to the brake shoes.
PARKING BRAKE
The parking brake on a ll 1/2, 3/4, and 1 ton m odels is
the m echanical type which u tilize s the action of the s e r v ­
ic e brake shoes in the r e a r brake assem blies. A ll other
m odels (except a ir sy stem s) are equipped with the p ro ­
p e lle r shaft type parking brake.
BRAKE PIPE DISTRIBUTION A N D
SWITCH ASSEMBLY (Fig. 9)
NOTE: The brake p ressu re d iffe re n tia l w arn­
ing switch is a non-adjustable, n o n -servicea b le
va lve. If d efective it must be replaced.
C A -P A -P A 1 0 -2 0 , C A -P A -3 0 m odels a re equipped with
a brake pipe distribution and switch assem bly. The front
and re a r hydraulic brake lin es a re
main cylin der, through the switch assem bly, to the front
and re a r brakes. The switch is w ired e le c tr ic a lly to the
brake alarm indicator light on the instrum ent panel. In
the event of fluid loss in eith er the front o r re a r brake
system , the indicator on the instrum ent panel w ill illu m i­
nate red when brake pedal is depressed.
Removal
1. Disconnect battery cable.
2. Disconnect e le c tr ic a l lead fro m
3. P la ce dry rags below the switch to absorb any fluid
s p illed during rem ova l of switch.
4. Disconnect fou r hydraulic lin es fro m connections at
switch. If n ecessa ry,
main cylin der to loosen lin es.
with clean, lin t-fr e e
m atter fro m entering the system .
5. R em ove mounting sc re w and rem ove switch fro m
veh icle.
Installation
1. Make sure new switch is clean and fr e e of dust and
lint. If any doubt exists, wash switch in D eclene or
equivalent, and dry with a ir.
v a r ie s on d ifferen t m odels,
and " FR 3A" type
On a Tw in­
routed from
switch assem bly.
loosen line connections at
C over open line ends
m a te ria l to preven t fo reig n
2. P la c e switch in position and secu re to bracket with
mounting screw .
3. Rem ove p ro tective
brake lines and connect lin es to switch. If n ecessary,
tighten brake
4. Connect switch e le c tr ic a l lead.
5. Connect battery cable.
6. B leed the brake system s as outlined in this section.
BRAKE W A R N IN G LIGHT
CHECKING PROCEDURE
1. D eterm in e if bulb is functioning.
2. Check to make sure that m aster cylin der r e s e r v o ir s
are full.
3. Open wheel cylin der bleed screw at one re a r wheel.
4. D ep ress brake
warning light should com e on due to p ressu re d if­
fe re n c e between fron t and re a r system s.
5. C lose bleed screw , then re le a s e brake pedal. R e fill
r e s e r v o ir , i f needed.
NOTE: Caution should be taken to preven t a ir
fro m entering hydraulic system during checks on
switch.
The recom m ended checking in terva l is 24 months o r
24,000 m iles, any tim e m ajor brake w ork is done o r any
tim e a custom er com plains of ex ce ss ive pedal tra vel.
BRAKE FAILURE W A R N IN G SWITCH (Fig. 9)
SA 40-60 s e r ie s with dual hydraulic brake system s
have a brake fa ilu re and tra v e l warning switch located
above the brake pedal pivot. A red ligh t is p rovid ed to
w arn the op erator of a brake line fa ilu re a nd-or ex c essive
brake pedal tra v e l.
The in dicator switch is w ire d so as to cause the bulb to
light in the ignition " sta rt"
functional bulb check.
Should the in dicator ligh t com e on during brake app li­
cation, the fo llo w in g conditions m ay ex ist and c o rr e c tiv e
action should be taken im m ediately:
the
1. H ydraulic leakage o r p ressu re loss.
2. L o ss of brake adjustment.
3. Severe usage o r w orn out brake linings.
m a teria l fro m open hydraulic
line connections at main cylin der,
pedal and hold down.
position p rovidin g fo r a
CHEVROLET TRUCK SERVICE MANUAL
BRAKES 5-5
The brake