Chevrolet 10 Series 1970 Service Manual page 269

DUO-SERVO
1 2 3 4
TWINPLEX
F ig . 57— Duo Servo and T w in p le x C y lin d e rs
1. Push Rod 3.
2. Boot 4.
TYPE "F"
TYPE "FR-3"
F ig . 5 8 —W heel C y lin d e rs Used w ith Types " F " , " F A " ,
" F R -3" and " F R -3 A "
1. Boot 4 . Piston Cup
2. Brake Shoe 5 . Cup F ille r
G u id e 6. Piston Spring
3. Piston 7. C y lin d e r
5 6
Piston
5. S pring
Piston Cup
6. Housing
Brakes
8. Brake Shoe
A n ch o r S lot
9. Push Rod
U-hooks fro m the cranks. Spread anchor crank C -
w ashers and lift o ff cranks (it is usually unneces­
sary to rem ove the starw heel cranks). I f shoes are
to be relined, rem ove adjuster eccen trics fro m the
shoe webs by unscrewing their self-tapp in g screw s.
5. R em ove shoe retraction
looped ends o ff of pins.
down lock w ire s , castellated nuts and plain washers
and lift o ff shoes.
6. Thread each adjuster screw fro m the shoe side o f
the anchor supports.
slots. Do not attempt to rem ove a fric tio n ring from
a screw ; i f necessary, rep lace the sc re w assem bly
instead.
7. To rem ove a wheel cylin der o r cylin d er co ver, r e ­
m ove connecting tubing and mounting screw s.
8. SHOE R E L IN E - If relin ed brake shoes are to be
su rface ground, set g rin d er 0.020 to 0.030 inch Jess
than standard drum diam eter in o rd er to p rovide a
" brake in " clearan ce at lining ends.
9. Check to make sure that backing plate and anchor
supports are clean and torqued to sp ecification s.
Installation (Fig. 56 )
1. When installing a wheel cylin der with co v e r, make
sure that the lon ger cylin der end, m easured fro m the
hydraulic port w ill face toward the shoe toe and s ta r­
wheel. Be sure cylin d er
torqued to specification s.
2. Insert starw heels in anchor support slots and thread
in adjuster screw s fro m the shoe side, fric tio n ring
end toward the shoe.
ju sters taking care not to jam the starw h eels.
not lubricate adjuster screw s.
NOTE: C are must be e x ercised not to damage
the frictio n ring on the adjusting screw during
assem bly in the anchor support.
way to start the ring and screw assem bly into
the anchor support counter bore is by co m p ress­
ing the rin g into its groove with long nose p lie rs
while starting the screw .
3. Install brake shoes by locating shoe with its toe (cut
away portion of web) positioned in the adjuster slot
heel in the anchor pin slot. Install hold-down bolt,
plain washer and castellated nut fin g er tight, then
back o ff nut one turn and in sert nut lo ck w ire. Install
retractin g springs in shoe web, longest shank at the
adjuster, and hook springs o v e r pins using T oo l
J-8049.
4. Install the adjuster hex eccen tric on each shoe web,
tightening the self-tap p in g screw only fin ger tight to
p erm it final adjustment o f eccen trics.
5. Locate anchor cranks on anchor pins, the long arm s
toward shoes, bushing toward backing plate, so that
they rotate fr e e ly while restin g against retractin g
spring hooks. In stall and crim p the C -w ash ers. At
each crank, assem ble the short link sm all hook in ­
to the short arm o f the crank fro m the lo w er side
and hook other link end around the eccen tric on the
shoe web. A ssem b le long link S-hook to long arm o f
crank fro m upper side,
that slot lines up with link U-hook, in sert U-hook and
rotate starw heel crank back to approxim ate adjust­
ing position. Install adjuster spring with short hook
on starw heel crank fin ger so that its long shank hook
BRAKES 5-31
springs by sliding their
Then rem ove shoe hold-
L ift starw heels fro m support
mounting screw s
F o r new linings, back o ff ad­
The ea siest
rotate starw heel crank so
CHEVROLET TRUCK SERVICE MANUAL
are
Do