Chevrolet 10 Series 1970 Service Manual page 254

BRAKES 5-16
F ig . 29—Brake M a in and C lu tc h Assist Type C y lin d e rs
1. M a in C y lin d e r
2. Return S pring
3. R eta in er
4. P rim ary Cup
NOTE: Be sure to keep parts clean until r e ­
assem bly. Rewash p arts, i f there is any o c ­
casion to doubt clean lin ess.
4. Check pistons fo r scratch es or other dam age; r e ­
place if n ecessary.
Assembly
Use care when reassem b lin g the main cylin d er check
v a lv e s . Im proper assem bly o f the check va lve seats w ill
resu lt in distortion of the seats. If this occu rs, there w ill
be no check valve action and a loss of brake pedal tra v e l
w ill result; the pedal w ill have to be pumped one o r m ore
tim es b efore actual c a r braking occu rs.
If Check V alves W e re R em o ved:
1. P la ce the main cy lin d er in a vis e
holes facing up. P la c e the check va lve springs in the
outlet holes. Be sure the springs are seated in the
bottom o f the holes.
o v e r the springs, being carefu l not to displace the
springs fro m the spring seats.
2. P lace new b rass tube seats in the outlet holes. Be
sure seats a re not cocked as this would cause burrs
to be turned up as the tube seats are p ressed in.
Thread a spare brake line tube into the outlet hole
and turn the nut down until the tube seat bottom s.
R em ove the tube nut and check the outlet hole fo r
loose bu rrs, which might have been turned up when
the tube seat was p re s s ed down. Repeat this p rocess
to bottom the second seat.
3. Put new secondary seals in the two grooves in the
end o f the secondary piston assem bly.
which is n earest the end w ill have its lip s facing to­
w ard that end. The seal in the second gro o ve should
have its lip s facing toward the portion o f the secon­
dary piston which contains the sm a ll compensating
holes.
4. A ssem b le a new p rim a ry seal p ro tector and p rim a ry
seal o v e r the end of the secondary piston with the
5. Piston
6. Piston Seal
7. Snap Ring
with the outlet
P la ce new rubber check va lves
The seal
fla t side o f the seal seats against the sea l p rotector,
and the p ro tecto r against the flange o f the piston
which contains the sm all com pensating holes.
5. A ssem b le the new secondary seal into the gro o ve on
the push rod end o f the p rim a ry piston. The lips o f
this seal should face toward the sm all compensating
holes in the opposite end o f the p rim a ry piston.
6. A ssem ble the new p rim a ry seal p ro tecto r and p r i ­
m ary seal on the end o f the p rim a ry piston with the
fla t side o f the seal seated against the seal p ro tecto r,
and the p ro te cto r against the flange on the piston
which contains the com pensating holes.
7. A ssem b le the spring reta in er in one end o f the p r i­
m ary piston spring and the secondary piston stop in
the other end. P la ce the end o f the spring o v e r the
end o f the p rim a ry piston with the spring retain er
seats inside o f the lips o f the p rim a ry seal.
8. Rem ove a ll cleaning liquid fro m the threaded hole in
the p rim a ry piston. P la ce the piston extension s crew
down through the secondary piston stop and the p r i­
m ary spring reta in er and s c re w it into the p rim a ry
piston until it bottoms out.
9. Coat the b ore o f the m aster cylin d er with clean brake
fluid. Coat the p rim a ry and secondary seals on the
secondary piston with clean brake fluid. Insert the
secondary piston spring reta in er into the secondary
piston spring. P la c e
o v e r the end o f the secondary piston until the r e ­
tain er locates inside of the lips o f the p rim a ry cup.
10. Hold the m aster cylin d er with the open end o f the
bore down. Push the secondary piston into the bore
until the spring seats against the closed end o f the
bore.
11. P osition the m aster cylin der in a v is e with the open
end o f the b ore up. Coat the p rim a ry and secondary
seal on the p rim a ry piston with clean brake fluid.
Push the p rim a ry piston assem bly, spring end fir s t,
into the b ore o f the m aster cylin der. Hold the piston
down and snap the lock ring into position in the sm all
gro o ve in the I.D. o f the b ore.
12. Push the p rim a ry piston down to move the secondary
piston fo rw a rd fa r enough to c le a r the stop screw
hole in the bottom o f the front fluid r e s e r v o ir . Install
the stop screw .
13. Install r e s e r v o ir diaphragm in the r e s e r v o ir co ve r
and in stall the c o v e r on the main cylin d er. Push ball
w ire into position to secu re the r e s e r v o ir co v e r.
Installation
1. A ssem b le the push rod through the push rod reta in er,
if it has been disassem bled.
2. Push the reta in er o v e r the end o f the main cylin d er.
A ssem b le new boot o v e r push rod and p re s s it down
o v e r the push rod reta in er. Slide new mounting g a s ­
ket into position.
3. Secure the main cylin d er to the fir e w a ll o r fram e
r a il as applicable, with mounting bolts.
4. Connect the push rod c le v is to the brake pedal with
pin and retain er.
5. Connect the brake lines to the main cylin d er.
6. F ill the main cylin der r e s e r v o ir s to the le v e ls shown
in F igu re 15. B leed the brake system as outlined in
this section.
7. If n ecessary, adjust the brake pedal fr e e play as out­
lined in this section.
the reta in er and spring down
CHEVROLET TRUCK SERVICE MANUAL