Chevrolet 70 Series 1970, Service Manual

Page: 655 / 841

TRANSMISSIONS AND CLUTCHES 7-56
2. Check p iston fit in cylinder b o re. C lea r­
an ce betw een p iston and cylinder w all should be
w ithin 0 .0 0 1 ” to 0.006" when checked with fe e le r
gauge.
A ssem b ly
1. B efo re a ssem b lin g , coat in sid e of cylinder
bore and dip a ll in tern al p a rts in hydraulic brake
fluid.
2. In sta ll com ponents in clutch cylinder bore
a s follow s:
a. In sta ll return sp rin g in cylinder b ore, with
la r g e d iam eter fir s t.
b. In sta ll prim ary cup in cylinder bore with
lip of cup toward outlet end. Make su r e end of
sp rin g s e a ts in sid e the cup.
c. In sert p iston and secondary cup into c y l­
inder b ore, w ith open end of piston toward open
end of cylin d er.
d. P r e s s p iston into cylinder bore, c o m p r e ss­
ing spring, and in sta ll snap ring in groove in b ore.
NOTE: In sta ll p iston stop plate in cylin d er
u se d on ”R" M odels. Make su re snap ring is fully
se a te d in groove.
3. Check clea ra n ce betw een edge of prim ary
cup and the b ypass port in each cylinder a s follow s:
a. F rom in sid e the r e s e r v o ir , in sert a straight
w ir e (tag w ire or any w ire of approxim ately 0.010"
diam eter) through the b yp ass port.
b. While m oving the w ire up and down in the
b yp ass p ort, push the p iston in v ery gently until a
slig h t drag i s fe lt on the w ir e . Check clea ra n ce
betw een end of p iston and snap ring. C learance
should be 0.035 inch m inim um . If le s s than 0.035-
in ch , the wrong s iz e cup or a sw ollen cup has been
in sta lled , or the p a rts w e r e im properly a ssem b led .
D isa sse m b le unit and r e a sse m b le , using the c o r ­
r e c t p a r ts.
4. In stall cover on cylin d er r e se r v o ir .
CLUTCH CONTROL SLAVE CYLINDER
Clutch control sla v e cylin d er a ssem b ly is
mounted at sid e of clutch housing o r tr a n sm issio n .
When cylinder is p r e ssu r iz e d it a ctiv a te s the
m echanical clutch r e le a s e fork or le v e r to d isen ­
gage clutch.
Components of cylin d er c o n sists of an alum ­
inum p iston with two captive block-type s e a ls (fig.
27). The return of the p iston on clutch apply is
provided for by the extern al return spring.
REMOVAL
1. R em ove return sp rin g from clutch r e le a s e
fork o r le v e r .
2. D iscon n ect fluid lin e at sla v e cylin d er.
3. R em ove b o lts retaining s la v e cylinder at
mounting, then rem ove cylin d er a ssem b ly .
DISASSEMBLY
NOTE: Key num bers in text r e fe r to figu re 27.
1. R em ove cylinder push rod (5) and push rod
boot (4) from cylin d er.
2. R em ove p iston retaining ring (6) from sla v e
cy lin d er, using a sm a ll sc r ew d riv er.
CAUTION: DO NOT mar bore of
cylinder body.
3. R em ove p iston a ssem b ly (7) w ith s e a ls (8)
from cylin d er body (3).
NOTE: P isto n can b e jarred from body or
sm a ll amount of a ir p r e ssu r e at lin e fitting w ill
fo r c e piston from b o re. Do not allow piston to be­
com e dam aged after it i s rem oved.
4 . If s e a ls (8) a re in good condition they need
not be rem oved.
INSPECTION
NOTE: Key num bers in tex t r e fe r to fig u re 27.
1. Inspect sla v e cylin d er b ore, making su re
that it is sm ooth. A sc o r e d o r damaged cylinder
body (3) m ust be replaced.
NOTE: B u rrs at the b ore sid e of in let port
can be rem oved by honing or by u s e o f crocu s
cloth.
2. Check piston s e a ls (8) if rem oved. Sw elling
o f s e a ls could be due to u se of im proper brake
fluid.
3. Check fit of the p iston in the cylin d er bore,
u sin g a fe e le r gauge. This clea ra n ce should be
from 0.002" to 0.004".
ASSEMBLY
NOTE: Key num bers in tex t re fe r to fig u re 27.
1. In stall s e a ls (8) into g rooves of p isto n (7)
with lip s of s e a ls p osition ed to fluid end of piston
(fig. 29).
2. Dip p iston and s e a ls in clean brake fluid,
then ca refu lly in sta ll p iston a sse m b ly in bore of
cy lin d er. R efer to figu re 19 for proper p osition of
p iston in cylin d er.
3. In stall retaining ring (6) in groove at open
end of cylin d er.
4. In stall boot (4) over push rod (5) and in­
sta ll rod and boot to s la v e cylin d er.
INSTALLATION
1. B olt sla v e cylinder a sse m b ly to mounting.
2. Adjust sla v e cylinder push rod clearan ce
a s outlined in th is sectio n under "Clutch Control
A djustm ents."
3. Attach hydraulic lin e to sla v e cylinder and
b leed a ir fro m sy ste m at s la v e cylinder bleed
fittin g. See "Bleeding System " p rev io u sly in this
se c tio n .
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL